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Current situation and trend of geophysical technology in CNPC
PETROLEUM EXPLORATION AND DEVELOPMENT Volume 37, Issue 1, February 2010 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2010, 37(1): 1–10.
RESEARCH PAPER
Current situation and trend of geophysical technology in CNPC Liu Zhenwu1,*, Sa Liming1, Dong Shitai2, Deng Zhiwen3, Xu Guangcheng2 1. China National Petroleum Corporation, Beijing 100724, China; 2. PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China; 3. Bureau of Geophysical Prospecting (BGP), Zhuozhou 072751, China
Abstract: Over several years of development, CNPC has become a powerful geophysical force. The company has taken an international leadership in overall onshore seismic capacity and has developed numerous unique geophysical technologies. CNPC is particularly known for developing world-leading seismic exploration technologies for application in complex mountainous areas and across Loess Tableland prospects. In high-end R&D programs, technologies such as high-density seismic data acquisition, digital acquisition systems, and multicomponent concepts have demonstrated value in describing complex reservoirs. CNPC’s independent innovation in petroleum geophysics has improved significantly. With respect to software and hardware, CNPC has produced integrated geophysical software and designed 2000-channel seismic data-acquisition systems that will soon go into mass production. To meet exploration and development demands and requirements specified by the Four Projects program, PetroChina will be guided by a technology road map that has been prepared and will continue to work on core geophysical equipment, software, and new geophysical approaches and technologies. Key words: CNPC, geophysical technology, seismic exploration, high-density seismic, trend
China National Petroleum Corporation (CNPC) is an energy-based enterprise focused on the upstream business sector of the petroleum industry. CNPC’s profit comes primarily from oil and gas exploration and development. After several decades of development, geophysical exploration technology within CNPC has advanced to a strong technical level and now plays important roles in increasing reserves and productivity and in sustaining oil and gas development in fields such as Daqing. However, geophysical technology must be enhanced to keep pace with the increasing complexity of hydrocarbon targets. CNPC can maximize E&P profits only by making breakthroughs in key technologies.
1 1.1
Status of CNPC geophysical technology General conditions of CNPC geophysical exploration
At the end of 2008, CNPC consisted of BGP, three specialized geophysical service companies, and eighteen research institutes, including RIPED. Currently, CNPC has 30 700 people engaged in prospecting, with more than 5 400 of these personnel doing scientific research. In addition, there are 181 seismic data-acquisition crews, with 59 of these working abroad, 9 VSP crews, and 19 non-seismic data crews. These
crews use 185 large-scale seismic recording systems that provide a total of 540 000 data channels. These systems are capable of acquiring 125 000 km of 2D data and 62 000 km2 of 3D data per year. In addition, CNPC has 31 700 CPUs that can be used for processing and interpretation, 380 data-processing software systems, and more than 500 interpretation software systems. These combined resources have enabled CNPC to become the world’s leading company in onshore geophysical operations. CNPC’s seismic data-acquisition services can be found both at home and abroad. At present, 122 seismic crews are working in 16 CNPC domestic oil and gas fields and in several areas of high interest to Sinopec, CNOOC, and China United Coalbed Methane Company Ltd. Over the past five years, these crews have acquired an average of 40 000 km of 2D data and 15 000 km2 of 3D data. In the international arena, 59 seismic crews operate in 22 countries on four continents. 53 of these crews work onshore, three operate in shallow and intermediate-zone water, and three operate in deep water. CNPC now has approximately 50-percent of the seismic data-acquisition market among OPEC and international oil companies.
Received date: 10 Jun. 2009; Revised date: 28 Sep. 2009. * Corresponding author. E-mail: [email protected] Copyright © 2010, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.
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1.2
CNPC geophysical technologies
1.2.1 Seismic techniques for complex mountainous terrain Mountain areas often have elevation differences of as much as 2 000 m. Rock outcrops tend to be rugged and overlapping, and the subsurface generally has complex faults and sometimes even salt beds. To improve data acquisition in such terrain, CNPC has developed numerous critical technologies: 1. wide-line with large-combination acquisition and 3D with large-combination acquisition, 2. use of satellite pictures and variable geometry concepts to optimize optimal locations for sources and receivers, 3. combined surface surveying and modeling, 4. improved static calculations, 5. prestack depth migration adapted for rough topography, and 6. velocity modeling, structural modeling, and depth domain interpretation. These technologies have increased the understanding of tectonic patterns associated with complex structural belts. Applying these technologies in the Kuqa Depression has allowed better recognition of decollement fault systems (Fig. 1). The improved identification of complex traps in the mid-western part of this depression paved the way for the large West-East Gas Transmission Project[1]. 1.2.2
Seismic desert technologies
Desert areas of interest in the Junggar and Qaidam Basins have surface layers of sand 300 m or more thick. Dunes are large, and the sand is loose and contains no pore water. Carbonate rocks, igneous rocks, and complex faults occur in the subsurface. CNPC has used the following approaches to develop seismic technology for such desert operations: 1. location-by-location depth design for wells, 2. flexible placements of source and receiver stations,
Fig. 1
3. 4. 5. 6. 7.
static corrections for surface dune layers, optimized selection of monitoring systems, prestack migration, reservoir characterization, and qualitative descriptions of carbonates having fractures and cavities. Using these technologies, deep formations in the desert areas of the Tarim, Qaidam, and Ordos Basins can now be evaluated with data having better signal-to-noise ratios. An example of the improved imaging of the Lower Carboniferous of the Junggar Basin is illustrated on Figure 2. More than 2×1011 m3 of reserves have been proved in deep igneous rocks with these technologies. 1.2.3
Seismic technologies for Loess Tableland
The Loess Tableland of China has 300 m of loose, low-velocity loess on the surface. No water table occurs within this loess layer. Reservoirs across the area have low porosity, low permeability, small thicknesses, and high heterogeneity. CNPC has developed several critical procedures to develop reservoirs in this environment: 1. meander, ravine-tableland, multi-line, and cross-line techniques, 2. noise removal using variable thresholds, 3. 4-field iteration to determine static corrections from first arrivals, 4. selection, configuration, and equalization of surface elements, 5. prestack migration, 6. paleo geomorphologic descriptions, 7. prediction of physical properties and hydrocarbon saturation of reservoirs, and 8. well locations selected with the “five diagrams and one table” procedure which improves the signal-to-noise of deep reflections (Fig. 3). Using these techniques, channels and foreset reflections
Keshen-2 regional structure pattern interpretations before & after seismic tackling, Kuqa Depression
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Fig. 2
Fig. 3
Well-tie seismic profile across wells Dixi 14 -Di 101 in Ludong- Wucaiwan area of Junggar Basin
Quality comparisons between seismic data of Pre/ Post high-density seismic in Changqing Jiyuan area
can now be observed in loess-covered areas. Applications of the technologies have resulted in discoveries of Changqing Xifeng, Jiyuan, Baibao, and South Sulige, which involve more than 100 million tons of oil and 100 billion m3 of gas. 1.2.4
Seismic technologies for transition zones
Transition zone areas involve marshes, agricultural facilities, rock reefs, and faults. To explore these environments, CNPC has developed: 1. advanced steering and positioning, 2. high accuracy positioning of geophones, 3. air gun array design, and 4. OBC acquisition.
These techniques have been important in operations in Bohai Bay. 1.2.5
Seismic technologies in mass urban areas
Seismic operations are difficult where there are high-rise buildings and a dense population. In some mass urban areas of China, fault systems and targeted formations are quite deep. Seismic data have to be acquired that allow shallow, intermediate, and deep geology to be analyzed. To accomplish this objective, CNPC has emphasized: 1. joint activities of well and seismic source operations, 2. using geological information to place well spots, 3. dynamic geometry adjustments,
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4. mapping underground pipelines, 5. non-vertical monitoring, and 6. combined processing of new and old seismic data. 1.2.6
High-accuracy seismic technologies for oil zones
Oil production occurs at locations where there are numerous noise-generating facilities on the Earth surface. Production zones may be at shallow, intermediate, or deep depths and also be associated with complex fault systems. CNPC has developed important methods to evaluate and monitor known oil production zones, including: 1. time-lapse 3D data acquisition, 2. small-bin surface surveying, 3. well positioning and design based on lithological and reservoir dynamics, 4. high accuracy static corrections, 5. joint area processing, and 6. reservoir characterization with prestack data. These methods have been used to study shallow, intermediate, and deep geology in frequency increments of 5 to10 Hz and resulted in new producing horizons being found. 1.2.7
Reservoir geophysical technology
Non-marine reservoirs are thin across China and are difficult to resolve with seismic data. These reservoirs also exhibit strong horizontal heterogeneity, which presents many challenges in establishing lateral correlations and in defining connected reservoir compartments. To overcome these challenges, CNPC has implemented: 1. wide-azimuth data acquisition, 2. data-processing procedures that preserve accurate amplitudes, frequencies, phases, and waveshapes, 3. relative calibration and tectonic inversion during inter-
Fig. 4
pretation, thin-bed inversion analysis, 3.5D seismic data acquisition, 4D seismic data acquisition, borehole seismic data acquisition, and combining geophysics, logging, and drilling concepts during interpretation. These approaches have been valuable when predicting distributions of oil and gas (Fig. 4). 4. 5. 6. 7. 8.
1.2.8 Integrated geophysical and geochemical exploration technology Special geological questions often have to be answered when exploring for oil and gas. For this reason, CNPC has developed several technologies that complement seismic exploration efforts, including: 1. high-density 3D gravity and magnetic data acquisition, 2. high-energy 3D electrical-magnetic data acquisition, 3. high-accuracy aeromagnetics, 4. IPR interpretation of 3D reservoirs using electric anomaly modes, and 5. joint inversion of seismic and gravity data. These procedures play important roles in predicting reservoir conditions in igneous rocks. 1.3
Geophysical technology contributions to CNPC E&P
In the 9-year time period from 2000 to 2008, 3D seismic data acquisition within CNPC increased from 7 841 km2 to 17 893 km2, an average annual increase of 10.9%. Over the same period, proven reserves grew from 7.5×108 tons to 11.7×108 tons, a healthy annual growth rate of 5.7%. Oil production increased in average increments of 3.6% over the same time span and rose from 11 817×104 tons to 15 730×104
Remaining oil prediction with 3.5D seismic data in northwest margin of Junggar Basin
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tons. It is evident that investments in geophysical technology correspond to increased reserves and production. New, high-resolution, 3D seismic data spanning 4533 km2 resulted in fundamental changes of the geological model used in Tazhong. Using regional prestack time migration, prestack prediction of reservoir properties, and 3D descriptions of fractured and karsted carbonate reservoirs, a connected reef complex was predicted at the slope break of Tazhong 1. This new geological concept was a major breakthrough that has resulted in more than 2×108 tons of oil reserves and nearly 2×1011 m3 of gas reserves. In the Su-5 and Tao-7 blocks of Sulige, 985 km2 of high-resolution 3D seismic data and 100 km2 of multicomponent 3D data were acquired and processed in which the basic frequency was increased from 20–35 Hz to 30–45 Hz. This increased signal frequency allowed thinner beds to be identified, and sand body distributions were better defined. Distributions of gas-bearing sands, extents of producing areas, and gas-production strategies were defined using these improved seismic data. As a result, development drilling success increased from 62% in 2006 to 88% in 2008. Using these seismic data, 143 non-commercial wells were avoided, representing an investment saving of 1.1 billion RMB. At the previous drilling success rate of 62%, 488 wells would have to have been drilled; whereas, for the improved success rate of 88%, only 345 wells had to be drilled. The unit cost of the 143 wells that did not have to be drilled is 8 million RMB. Because the total investment in new seismic data over this 3-year period in the Su-5 and Tao-7 areas was only 275 million RMB, the total savings in E&P investment was 825 million RMB.
2 Development and progress of high-end technology CNPC emphasizes development of high-end technology
and has achieved outstanding success in developing cuttingedge concepts, software, and equipment. Examples of these successes are high-density seismic data, three distinct software systems protected as intellectual property, and largescale seismic equipment, vibrators, and drilling rigs. All of these technologies have been put into production. 2.1 Major progress on cutting-edge geophysical technology 2.1.1
High-density seismic technology
CNPC has been doing high-density seismic pilot studies since 2003. These activities have involved optimized system monitoring methods that create continuous spatial sampling and CRP coverage and minimal footprint effects. Studies have focused on relationships among line density, shot density, overlapping recording time, and techniques that define the smallest data effort that will satisfy noise removal and proper migration methods. 3D prestack noise analysis and highfidelity data-processing methods were included in these studies. Higher density channels have resulted in better spatial resolution, detection of smaller reservoir features, and improved oil and gas development. For example, 6.25 m×6.25 m surface elements and a trace density of 61×104 traces/km2 were adopted in the Hong-18 well area of the northwest margin of Junggar. As a result, the dominant frequency across deep- target intervals is greater than 60 Hz, which is 20 Hz greater than what had been achieved before. The ability to detect small faults was greatly improved (Fig. 5)[2]. 2.1.2
Multi-wave seismic technology
CNPC has utilized multi-wave seismic technology since 2002. These efforts have included acquisition of 3D con-
Fig. 5 Comparison between high-density seismic profile and conventional seismic profile of Hong-18 well area on northwest margin of Junggar
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Fig. 6
Gas enrichment area prediction with 3D multi-wave inversion in Su31-13 well area
verted-wave data, combined P and S seismic programs, recording 3-component micro logs, developing processing and interpretation techniques for P, S, and converted-wave data, determining static corrections for converted-wave data, and optimizing velocity analyses for multi-wave data. Emphasis has been placed on anisotropic data processing, identifying depth-equivalent strata in P and S data, and combining P and S attributes such as amplitudes and other waveform features. Numerous valuable results occurred, such as the interpretation of the He-8 pay zone interval. This reservoir is difficult to identify because it is a thin- bed system with interfingering sand and shale units. Using P-wave prestack elastic inversion, prestack AVO behavior, attenuation analysis, and interpretations of P and S waveforms, amplitude ratios, VP/VS velocity ratios and other multi-wave techniques, reservoir prediction success has increased from 60% to 80% (Fig. 6)[3].
surveys. These 4D seismic techniques identified locations of remaining oil in Cainan oil field in Xinjiang Province. An irregular drilling pattern was introduced that increased daily production by 40%. In 2008, two 7-km2 surveys were done at Huanxiling oil field in Liaohe using 6.25 m×6.25 m surface elements and VSP data acquired in two wells. A differential analysis of seismic attributes and a specialized visualization technique showed physical properties of the reservoir and identified fluid distributions so locations of remaining oil could be defined. The objective of this project was to use high-density 3D seismic technology in the secondary recovery stage of the field to find 5×107 tons of remaining oil in Shuguang oil field and to implement a dynamic monitoring technique suitable for heavy oil reservoirs occurring in non-marine sediments across China.
2.1.3
2.2 Successful developments of seismic acquisition, processing, and interpretation software
Full digital seismic technology
Full digital seismic production in CNPC started in 2004. High-resolution of low impedance-contrast zones and development of methods for broad-frequency recording, noise reduction, and improved data processing have combined to produce improved signal data. One example of these strategies being successfully applied is the full-digital data acquired with 5-m line intervals across the Chepaizi area of Junggar. These data revealed the spatial distributions of thin-bed sands in the last series of the Shawan group and reduced drilling risk. Quantitative analysis showed that the dominant frequency of digital data increased 30 Hz, 20 Hz, and 15 Hz for deep, intermediate, and shallow intervals, respectively, compared to the dominant frequencies of analog data. Digital data have provided higher geologic resolution and much better characterization of faults and lithological traps[4]. 2.1.4
Time migrated 4D seismic technology
CNPC has carried out 4D seismic experiments across Xinjiang, Liaohe, Daqing, and Jidong oil fields. This program has included feasibility studies, dual-acquisition consistency analysis, and development of data-processing techniques that ensure equivalent seismic properties are preserved in repeated
2.2.1
KlSeis seismic acquisition engineering software
CNPC began software development in 1998 to reduce the demands for importing technologies and to strengthen the company’s ability to address specific operational challenges. Software system KlSeis was released in 2000 and has now been updated to version 4.0. Important modules deal with acquisition design, forward modeling, static corrections, and quality control. These modules can be applied to a wide variety of seismic acquisition efforts, including P-wave, multiwave, VSP, and streamer projects. An English version of the software was released in 2002 for applications in overseas areas such as the Middle East, Central Asia, and Africa. This decision has resulted in both economic and social benefits, improved CNPC’s competiveness in international markets, and boosted CNPC’s stature as a service provider. 2.2.2 GeoMountain acquisition, processing, and interpretation software CNPC initiated the development of its GeoMountain software to benefit from the company’s many years of seismic
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experience in complex mountainous terrains. GeoMountain version 1.0 is now released. This software focuses on a wide variety of seismic data acquisition, processing, interpretation, and multi-wave applications. Featured technologies include: Forward modeling and target illumination analysis for mountainous terrains, Near-surface modeling, static corrections, and noise removal specialized for mountainous areas, Interpretation analysis that allows reverse fault mapping, fracture prediction, and identification of flow units, and Specialized modules that allow multi-component static corrections, prestack inversion, and joint inversion of P and S data. 2.2.3 GeoEast seismic data processing and interpretation integrated software CNPC began research to develop large-scale seismic data processing and interpretation in 2003 to improve the company’s competency in fundamental seismic operations and to minimize dependence on imported software. GeoEast version 1.0 was released in 2005. Over the next three years, numerous functions were added, algorithms were upgraded, and GeoEast version 2.0 is now available. Offshore, multi-wave, and VSP functions were added to the processing module, and post-stack inversion and reservoir prediction capabilities were added to the interpretation module. The interpretation performance of the software is equivalent to that provided by international software vendors and has unique features of value to CNPC. The development of GeoEast software has provided CNPC valuable intellectual property, allowed competitive advantages of foreign geophysical software to be overcome, provided economic benefits, and improved CNPC’s competiveness in the international seismic contractor market.
Fig. 7
2.3 Successful developments of seismic acquisition equipment 2.3.1
Large-scale seismic acquisition system
In 2006, CNPC launched a project, “Development of Novel Seismic Data Acquisition and Recording System”. Design objectives were achieved in 2008. The CNPC system offers a high-speed data transmission of 40 megabits/s, compared to 16 megabits/s for the Sercel 428 and 8 megabits/s for ION’s System IV. Software development and 60-channel prototype tests were finished in May 2008. Field tests and pilot operations of a 2000-channel system were done in February 2009. Data quality is equivalent to that of systems available from international manufacturers. A comparison of the CNPC system and ION’s Aries technology is shown as Figure 7. The commercialization plan is to manufacture a 20 000-channel system having a 2 ms sample rate in 2010. Manufacture of large-scale seismic systems will reduce the cost of purchasing from foreign providers, increase CNPC’s competitive strength, and build CNPC’s image as a reliable developer of critical technology. 2.3.2
Heavy-duty vibrator
CNPC regards the development of seismic vibrators, shot-hole drilling rigs, swamp equipment, and explosive shooting boxes as important components of its equipment development plans. KZ-28 articulated vibrators and KZ-30 tracked and wheeled vibrators have been developed to satisfy seismic source demands in difficult conditions such as rough topography, deserts, soft-ground terrains, and winter operations. The KZ-34 heavy-duty vibrator uses an innovative guide-pin hydraulic oil lubrication structure, a high-low leather bag accumulator, and a chassis with hinge-type steering gear that transmits more energy into the ground. Fewer vibrators are needed to do proper imaging, and data quality is
Comparison between seismic profiles acquired from same lines with self-developed large-size tools and Aries tools
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improved. These features have resulted in three patents related to the KZ-34 vibrator. Several KZ-28, KZ-30, and KZ-34 vibrators are in operational use. 2.3.3
Seismic drilling rig and carrier
Drilling rigs capable of drilling 80-m holes have been developed for use in mountainous, swampy, and desert terrains. ZCF-06, ZCF-08, and ZCF-32 caterpillar-tracked floating carriers, ZCL-12 wheeled swamp vehicles, and ZJL-01 light-duty hinge-type swamp vehicles have been developed to work in intertidal zones.
3
Challenges to geophysical technology
To meet the demands of oil and gas development required for the national economy, CNPC has proposed four projects for the last three years of the “11th five-year plan”, and these programs should also extend across the period of the “12th five-year plan”. These programs are: Reserve plateau project, Secondary development project, Natural gas grand development project, and Overseas project. With slight variations in focus, these four projects cover the entire CNPC E&P business operation. Geological objectives in these projects will concentrate on complex steep-dip structures, stratigraphic traps, deep carbonate rocks, deep igneous rocks, and secondary development of existing oil fields. There will be many geophysical challenges over the lifetime of these projects. 3.1
Complex steep-dip structures
Complex steep-dip structures occur in the Kuqa and southwestern areas of the Tarim Basin, along the southern edge of the Junggar Basin, in the Dabashan portion of Sichuan, the mountain front of Logmen Mountain, the west wing of the Ordos Basin, northern part of Qaidam, the Kulong Mountain area of Yumen, and other places in the Middle East, South America, and Africa that are of interest to CNPC. These areas are key components of the strategy to “stabilize the west and boost overseas business”. Major problems that have to be overcome involve complex topography, large variations in elevation, complicated lithologies, and low-impedance intervals. Also subsurface structures are complex, with issues being sub-salt tectonics, reverse structures, and strike-slip faults that combine to make seismic wave propagation difficult to manage. Even though technical studies have been done for several years, seismic profiles and geological models often do not match well. The challenges are to improve the resolution of seismic images (the goal being 100 m of tectonic resolution), enhance the imaging of high-dip structure associated with overthrust faults (the goal being to increase the success rate of correct structural interpretation by 20%), and confirm proper structure for development purposes (the goal being to shorten the time of the exploration phase by 20% to 40%).
3.2
Complex topography and stratigraphic traps
Stratigraphically trapped reserves occur in shallow and intermediate depth formations in Bohai Bay, and portions of the Songliao, Ordos, Tarim, Junggar, Tuha, Qaidam, Sanhu, and Sichuan Basins, as well as in other areas of Central Asia, Asia Pacific, and Africa. Operations in these areas are essential for reserve growth. Problems that have to be overcome are thick surface layers of sand and loess, thick weathered zones, complex and heterogenous sedimentation patterns, and thin reservoirs with low porosity, low permeability, and complex gas-water relationships[5–7]. High-resolution seismic data cannot identify individual reservoirs thinner than 3 m. The geophysical challenge is to increase the dominant frequency of seismic data by 10 Hz in western areas of China and by 10 to 15 Hz in eastern areas, with the objective of increasing the drilling success of stratigraphic traps by 20%. 3.3
Imaging deep carbonate and igneous rocks
Carbonate and igneous rocks are the future of natural gas development in China. Carbonate rocks are distributed across Tarim, Sichuan, and Ordos Basins, Bohai Bay, southern China, central Asia, Asia Pacific, and the Middle East. The difficulties associated with carbonates are that reservoirs are deep and heterogeneous. In some case, carbonate structures are below salt, which makes imaging difficult, and in other cases it is essential to define distributions of fractures and karsted cavities. Petrophysical predictions of oil in place are difficult because of complex relationships among water, gas, and oil in carbonates[8]. Geophysical challenges are to improve seismic resolution to the range of 15 to 30 m, with an 80% success rate for predicting carbonate reservoirs of this size, to quantify fractures and cavities, and to create a 10 to 20% increase in successful E&P projects. Igneous rocks are found in deep formations across the Songliao and Junggar Basins, Bohai Bay, and a few other locations. Major problems that affect exploration of igneous rocks are their great depth of burial, their associated complex tectonic forms that make imaging difficult, poor signal-to-noise ratios of deep seismic data, inadequate resolution, and low prediction success of reservoir conditions and hydrocarbon occurrence[9]. Technical challenges are to increase the signal-to-noise ratio of deep reflections by 50%, enhance reservoir resolution to 15 to 30 m with an 80% prediction accuracy, and raise the E&P success rate by 10 to 20%. 3.4
Geophysical challenges of old fields
The term “old fields” refers to areas of Bohai Bay, the Daqing Changyuan area of the Songliao Basin, the northwest part of the Junggar Basin, and the southwest portion of the Qaidam Basin. To assist the operation of old fields, it is essential to perform reservoir characterization, define isolated reservoir compartments, and locate stratigraphic traps and new producing strata. Problems that have to be resolved are detecting individual thin beds, understanding how thin sand and
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shale units are meshed together in complex patterns, locating narrow channels with widths of 300 to 600 m, predicting rock properties in conditions of low porosity and permeability, detecting faults with small vertical throws, and overcoming the limitations of low signal-to-noise and low-resolution deep data. It will be necessary to define targets that are less than 3 m thick and only a few tens of meters wide. These thin, heterogeneous targets are difficult to define for horizontal-well and multi-well drilling programs. Technical challenges are to predict traps only 1 to 3 m thick in the east and 3 to 7 m thick in the west, detect faults with throws of only 3 to 5 m in the east and 5 to 10 m in the west, and establish reservoir modeling that will result in efficient secondary development.
4
Direction for geophysical development
CNPC is confronted with monumental difficulties such as complex mountainous areas, large regions covered by loess tablelands, reservoirs with super-low porosities and permeabilities, and thin-bed targets. Geophysical technology is challenged in every sector of E&P[10]. To meet these challenges, CNPC has formulated a geophysical technology development blueprint (Fig. 8) that provides paths for developing 2D and 3D descriptions, 3D visualization, and 4D monitoring of reservoir systems. In support of exploration, attention will focus on gravity, magnetic, and electrical technologies, seismic acquisition in complex-surface areas, prestack depth migration, and prestack reservoir prediction and trap
Fig. 8
evaluation. Seismic technology will dominate the evaluation phase, with emphasis placed on more accurate 3D seismic and prestack seismic property descriptions, fluid identification, qualitative and semi-quantitative trap evaluation, and reservoir modeling. For the development phase, priorities will be placed on digital seismic, high-density seismic, multi-wave, borehole seismic, 4D seismic, fluid identification, and dynamic reservoir modeling. Integrated seismic, well logging, and drilling engineering will be integrated in a 4D style to support secondary development. Continuous improvements in geophysical software and hardware will occur to ensure a smooth implementation of CNPC’s “Four Great Projects” and co-development of onshore and offshore prospects. CNPC has established four general objectives for technology development. In terms of challenges, these objectives are: Stratigraphic traps: Increase the fundamental frequency of seismic data by 5 to 10 Hz and achieve prediction accuracies of target thicknesses of 1 to 3 m in the east and 3 to 7 m in the west. Complex mountainous areas: Improve seismic imaging accuracy to 100 m and shorten the exploration cycle by 20 to 40%. Reservoir identification and prediction: Predict reservoirs with an accuracy of 15 to 30 m with a prediction success of 80% or more, and improve E&P success in predicting carbonate and igeneous reservoirs by 10 to 20%.
Blueprint of geophysical technology development for CNPC
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Old fields and secondary development: Identify faults and structures having vertical reliefs of 3 to 5 m in the east and 5 to 10 m in the west, with prediction successes of 80% and 70%, respectively, in the east and west, and implement dynamic reservoir monitoring. To achieve these objectives and to address these challenges, CNPC has defined several directions in which technology improvements will occur in core software and hardware efforts and in new geophysical methods. Core development of geophysical equipment and software 10 000-channel data acquisition system Digital geophone Electro-magnetic vibrator Onshore 3D electrical-magnetic system Deep-water exploration equipment Seismic acquisition design and quality control software Seismic processing and interpretation software Special software for reservoir prediction and fluid monitoring Software for geochemical and non-seismic acquisition, processing, and interpretation New geophysical methods Petrophysical analysis technques Petrophysical characterization of heterogeneous reservoirs Anisotropic velocity modeling and imaging technologies for complex structures High-density seismic exploration Multi-wave and multi-component exploration techniques Time migration algorithms Well-to-field joint exploration Deep water streamer and OBC exploration technologies Offshore electromagnetic technology Coal bed methane geophysical technologies Micro-seismic monitoring capability A successful execution of this blueprint plan will result in continuous expansion of CNPC geophysical technologies and services. A fundamental intent is to extend capabilities and services across a wider spectrum of several areas, ranging from structural traps to depositional traps, poststack to prestack, time domain to depth domain, qualitative to quantitative descriptions, reservoir prediction to hydrocarbon monitoring, and post-event to pre-event analysis. Additional goals are to extend the CNPC technical chain from exploration to development so as to span the entire life cycle of oilfields, and to expand CNPC’s business chain across multiple fields such as reservoir, offshore, software, hardware, and information. In the services sector, objectives
are to change the CNPC service pattern from a singular focus to integrated packages in which CNPC will offer company and contractor services ranging from exploration design and reservoir description to well placement and reserves reports, expand the CNPC service market from home to abroad, and shift from domestic markets to high-end markets that serve international major oil companies.
5
Conclusions
By implementing integrated scientific and technical programs, emphasizing new technology applications and research, and strengthening technology transfer, CNPC will develop geophysical technologies that can be applied to foreland fault areas, stratigraphic traps, and carbonate and igneous rocks. High-density seismic, multi-wave, time-migration seismic, borehole seismic, and reservoir geophysics will be developed that will allow reservoir identification to be improved from the 10 to 15 m thickness range to the 1 to 3 m range, improve operational success from 60% to 70%, and remove bottlenecks in E&P projects. To strengthen the development of core software and equipment, the following objectives must be achieved by the end of the “12th five-year plan”: 1. a reservoir-oriented integrated software system based on GeoEast, 2. internal seismic equipment that meets high technical and economic standards and can be commercialized, 3. more than 90% of the home market for vibrators, 4. ownership of 8 to 10 streamer ships, 5. design techniques for streamer deployment and retrieval, 6. trial production of streamers, and 7. know-how related to deep water towing, OBC and electromagnetic operation. By promoting proven technologies, tackling bottlenecks, keeping abreast of emerging technologies, and development of hardware and software systems, CNPC geophysical technology will improve, and will steer the upstream business toward emphasis on seismic technologies that will reduce exploration cost by using fewer wells to achieve greater value and higher efficiency.
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RESEARCH PAPER
Current situation and trend of geophysical technology in CNPC Liu Zhenwu1,*, Sa Liming1, Dong Shitai2, Deng Zhiwen3, Xu Guangcheng2 1. China National Petroleum Corporation, Beijing 100724, China; 2. PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China; 3. Bureau of Geophysical Prospecting (BGP), Zhuozhou 072751, China
Abstract: Over several years of development, CNPC has become a powerful geophysical force. The company has taken an international leadership in overall onshore seismic capacity and has developed numerous unique geophysical technologies. CNPC is particularly known for developing world-leading seismic exploration technologies for application in complex mountainous areas and across Loess Tableland prospects. In high-end R&D programs, technologies such as high-density seismic data acquisition, digital acquisition systems, and multicomponent concepts have demonstrated value in describing complex reservoirs. CNPC’s independent innovation in petroleum geophysics has improved significantly. With respect to software and hardware, CNPC has produced integrated geophysical software and designed 2000-channel seismic data-acquisition systems that will soon go into mass production. To meet exploration and development demands and requirements specified by the Four Projects program, PetroChina will be guided by a technology road map that has been prepared and will continue to work on core geophysical equipment, software, and new geophysical approaches and technologies. Key words: CNPC, geophysical technology, seismic exploration, high-density seismic, trend
China National Petroleum Corporation (CNPC) is an energy-based enterprise focused on the upstream business sector of the petroleum industry. CNPC’s profit comes primarily from oil and gas exploration and development. After several decades of development, geophysical exploration technology within CNPC has advanced to a strong technical level and now plays important roles in increasing reserves and productivity and in sustaining oil and gas development in fields such as Daqing. However, geophysical technology must be enhanced to keep pace with the increasing complexity of hydrocarbon targets. CNPC can maximize E&P profits only by making breakthroughs in key technologies.
1 1.1
Status of CNPC geophysical technology General conditions of CNPC geophysical exploration
At the end of 2008, CNPC consisted of BGP, three specialized geophysical service companies, and eighteen research institutes, including RIPED. Currently, CNPC has 30 700 people engaged in prospecting, with more than 5 400 of these personnel doing scientific research. In addition, there are 181 seismic data-acquisition crews, with 59 of these working abroad, 9 VSP crews, and 19 non-seismic data crews. These
crews use 185 large-scale seismic recording systems that provide a total of 540 000 data channels. These systems are capable of acquiring 125 000 km of 2D data and 62 000 km2 of 3D data per year. In addition, CNPC has 31 700 CPUs that can be used for processing and interpretation, 380 data-processing software systems, and more than 500 interpretation software systems. These combined resources have enabled CNPC to become the world’s leading company in onshore geophysical operations. CNPC’s seismic data-acquisition services can be found both at home and abroad. At present, 122 seismic crews are working in 16 CNPC domestic oil and gas fields and in several areas of high interest to Sinopec, CNOOC, and China United Coalbed Methane Company Ltd. Over the past five years, these crews have acquired an average of 40 000 km of 2D data and 15 000 km2 of 3D data. In the international arena, 59 seismic crews operate in 22 countries on four continents. 53 of these crews work onshore, three operate in shallow and intermediate-zone water, and three operate in deep water. CNPC now has approximately 50-percent of the seismic data-acquisition market among OPEC and international oil companies.
Received date: 10 Jun. 2009; Revised date: 28 Sep. 2009. * Corresponding author. E-mail: [email protected] Copyright © 2010, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.
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1.2
CNPC geophysical technologies
1.2.1 Seismic techniques for complex mountainous terrain Mountain areas often have elevation differences of as much as 2 000 m. Rock outcrops tend to be rugged and overlapping, and the subsurface generally has complex faults and sometimes even salt beds. To improve data acquisition in such terrain, CNPC has developed numerous critical technologies: 1. wide-line with large-combination acquisition and 3D with large-combination acquisition, 2. use of satellite pictures and variable geometry concepts to optimize optimal locations for sources and receivers, 3. combined surface surveying and modeling, 4. improved static calculations, 5. prestack depth migration adapted for rough topography, and 6. velocity modeling, structural modeling, and depth domain interpretation. These technologies have increased the understanding of tectonic patterns associated with complex structural belts. Applying these technologies in the Kuqa Depression has allowed better recognition of decollement fault systems (Fig. 1). The improved identification of complex traps in the mid-western part of this depression paved the way for the large West-East Gas Transmission Project[1]. 1.2.2
Seismic desert technologies
Desert areas of interest in the Junggar and Qaidam Basins have surface layers of sand 300 m or more thick. Dunes are large, and the sand is loose and contains no pore water. Carbonate rocks, igneous rocks, and complex faults occur in the subsurface. CNPC has used the following approaches to develop seismic technology for such desert operations: 1. location-by-location depth design for wells, 2. flexible placements of source and receiver stations,
Fig. 1
3. 4. 5. 6. 7.
static corrections for surface dune layers, optimized selection of monitoring systems, prestack migration, reservoir characterization, and qualitative descriptions of carbonates having fractures and cavities. Using these technologies, deep formations in the desert areas of the Tarim, Qaidam, and Ordos Basins can now be evaluated with data having better signal-to-noise ratios. An example of the improved imaging of the Lower Carboniferous of the Junggar Basin is illustrated on Figure 2. More than 2×1011 m3 of reserves have been proved in deep igneous rocks with these technologies. 1.2.3
Seismic technologies for Loess Tableland
The Loess Tableland of China has 300 m of loose, low-velocity loess on the surface. No water table occurs within this loess layer. Reservoirs across the area have low porosity, low permeability, small thicknesses, and high heterogeneity. CNPC has developed several critical procedures to develop reservoirs in this environment: 1. meander, ravine-tableland, multi-line, and cross-line techniques, 2. noise removal using variable thresholds, 3. 4-field iteration to determine static corrections from first arrivals, 4. selection, configuration, and equalization of surface elements, 5. prestack migration, 6. paleo geomorphologic descriptions, 7. prediction of physical properties and hydrocarbon saturation of reservoirs, and 8. well locations selected with the “five diagrams and one table” procedure which improves the signal-to-noise of deep reflections (Fig. 3). Using these techniques, channels and foreset reflections
Keshen-2 regional structure pattern interpretations before & after seismic tackling, Kuqa Depression
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Fig. 2
Fig. 3
Well-tie seismic profile across wells Dixi 14 -Di 101 in Ludong- Wucaiwan area of Junggar Basin
Quality comparisons between seismic data of Pre/ Post high-density seismic in Changqing Jiyuan area
can now be observed in loess-covered areas. Applications of the technologies have resulted in discoveries of Changqing Xifeng, Jiyuan, Baibao, and South Sulige, which involve more than 100 million tons of oil and 100 billion m3 of gas. 1.2.4
Seismic technologies for transition zones
Transition zone areas involve marshes, agricultural facilities, rock reefs, and faults. To explore these environments, CNPC has developed: 1. advanced steering and positioning, 2. high accuracy positioning of geophones, 3. air gun array design, and 4. OBC acquisition.
These techniques have been important in operations in Bohai Bay. 1.2.5
Seismic technologies in mass urban areas
Seismic operations are difficult where there are high-rise buildings and a dense population. In some mass urban areas of China, fault systems and targeted formations are quite deep. Seismic data have to be acquired that allow shallow, intermediate, and deep geology to be analyzed. To accomplish this objective, CNPC has emphasized: 1. joint activities of well and seismic source operations, 2. using geological information to place well spots, 3. dynamic geometry adjustments,
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4. mapping underground pipelines, 5. non-vertical monitoring, and 6. combined processing of new and old seismic data. 1.2.6
High-accuracy seismic technologies for oil zones
Oil production occurs at locations where there are numerous noise-generating facilities on the Earth surface. Production zones may be at shallow, intermediate, or deep depths and also be associated with complex fault systems. CNPC has developed important methods to evaluate and monitor known oil production zones, including: 1. time-lapse 3D data acquisition, 2. small-bin surface surveying, 3. well positioning and design based on lithological and reservoir dynamics, 4. high accuracy static corrections, 5. joint area processing, and 6. reservoir characterization with prestack data. These methods have been used to study shallow, intermediate, and deep geology in frequency increments of 5 to10 Hz and resulted in new producing horizons being found. 1.2.7
Reservoir geophysical technology
Non-marine reservoirs are thin across China and are difficult to resolve with seismic data. These reservoirs also exhibit strong horizontal heterogeneity, which presents many challenges in establishing lateral correlations and in defining connected reservoir compartments. To overcome these challenges, CNPC has implemented: 1. wide-azimuth data acquisition, 2. data-processing procedures that preserve accurate amplitudes, frequencies, phases, and waveshapes, 3. relative calibration and tectonic inversion during inter-
Fig. 4
pretation, thin-bed inversion analysis, 3.5D seismic data acquisition, 4D seismic data acquisition, borehole seismic data acquisition, and combining geophysics, logging, and drilling concepts during interpretation. These approaches have been valuable when predicting distributions of oil and gas (Fig. 4). 4. 5. 6. 7. 8.
1.2.8 Integrated geophysical and geochemical exploration technology Special geological questions often have to be answered when exploring for oil and gas. For this reason, CNPC has developed several technologies that complement seismic exploration efforts, including: 1. high-density 3D gravity and magnetic data acquisition, 2. high-energy 3D electrical-magnetic data acquisition, 3. high-accuracy aeromagnetics, 4. IPR interpretation of 3D reservoirs using electric anomaly modes, and 5. joint inversion of seismic and gravity data. These procedures play important roles in predicting reservoir conditions in igneous rocks. 1.3
Geophysical technology contributions to CNPC E&P
In the 9-year time period from 2000 to 2008, 3D seismic data acquisition within CNPC increased from 7 841 km2 to 17 893 km2, an average annual increase of 10.9%. Over the same period, proven reserves grew from 7.5×108 tons to 11.7×108 tons, a healthy annual growth rate of 5.7%. Oil production increased in average increments of 3.6% over the same time span and rose from 11 817×104 tons to 15 730×104
Remaining oil prediction with 3.5D seismic data in northwest margin of Junggar Basin
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tons. It is evident that investments in geophysical technology correspond to increased reserves and production. New, high-resolution, 3D seismic data spanning 4533 km2 resulted in fundamental changes of the geological model used in Tazhong. Using regional prestack time migration, prestack prediction of reservoir properties, and 3D descriptions of fractured and karsted carbonate reservoirs, a connected reef complex was predicted at the slope break of Tazhong 1. This new geological concept was a major breakthrough that has resulted in more than 2×108 tons of oil reserves and nearly 2×1011 m3 of gas reserves. In the Su-5 and Tao-7 blocks of Sulige, 985 km2 of high-resolution 3D seismic data and 100 km2 of multicomponent 3D data were acquired and processed in which the basic frequency was increased from 20–35 Hz to 30–45 Hz. This increased signal frequency allowed thinner beds to be identified, and sand body distributions were better defined. Distributions of gas-bearing sands, extents of producing areas, and gas-production strategies were defined using these improved seismic data. As a result, development drilling success increased from 62% in 2006 to 88% in 2008. Using these seismic data, 143 non-commercial wells were avoided, representing an investment saving of 1.1 billion RMB. At the previous drilling success rate of 62%, 488 wells would have to have been drilled; whereas, for the improved success rate of 88%, only 345 wells had to be drilled. The unit cost of the 143 wells that did not have to be drilled is 8 million RMB. Because the total investment in new seismic data over this 3-year period in the Su-5 and Tao-7 areas was only 275 million RMB, the total savings in E&P investment was 825 million RMB.
2 Development and progress of high-end technology CNPC emphasizes development of high-end technology
and has achieved outstanding success in developing cuttingedge concepts, software, and equipment. Examples of these successes are high-density seismic data, three distinct software systems protected as intellectual property, and largescale seismic equipment, vibrators, and drilling rigs. All of these technologies have been put into production. 2.1 Major progress on cutting-edge geophysical technology 2.1.1
High-density seismic technology
CNPC has been doing high-density seismic pilot studies since 2003. These activities have involved optimized system monitoring methods that create continuous spatial sampling and CRP coverage and minimal footprint effects. Studies have focused on relationships among line density, shot density, overlapping recording time, and techniques that define the smallest data effort that will satisfy noise removal and proper migration methods. 3D prestack noise analysis and highfidelity data-processing methods were included in these studies. Higher density channels have resulted in better spatial resolution, detection of smaller reservoir features, and improved oil and gas development. For example, 6.25 m×6.25 m surface elements and a trace density of 61×104 traces/km2 were adopted in the Hong-18 well area of the northwest margin of Junggar. As a result, the dominant frequency across deep- target intervals is greater than 60 Hz, which is 20 Hz greater than what had been achieved before. The ability to detect small faults was greatly improved (Fig. 5)[2]. 2.1.2
Multi-wave seismic technology
CNPC has utilized multi-wave seismic technology since 2002. These efforts have included acquisition of 3D con-
Fig. 5 Comparison between high-density seismic profile and conventional seismic profile of Hong-18 well area on northwest margin of Junggar
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Fig. 6
Gas enrichment area prediction with 3D multi-wave inversion in Su31-13 well area
verted-wave data, combined P and S seismic programs, recording 3-component micro logs, developing processing and interpretation techniques for P, S, and converted-wave data, determining static corrections for converted-wave data, and optimizing velocity analyses for multi-wave data. Emphasis has been placed on anisotropic data processing, identifying depth-equivalent strata in P and S data, and combining P and S attributes such as amplitudes and other waveform features. Numerous valuable results occurred, such as the interpretation of the He-8 pay zone interval. This reservoir is difficult to identify because it is a thin- bed system with interfingering sand and shale units. Using P-wave prestack elastic inversion, prestack AVO behavior, attenuation analysis, and interpretations of P and S waveforms, amplitude ratios, VP/VS velocity ratios and other multi-wave techniques, reservoir prediction success has increased from 60% to 80% (Fig. 6)[3].
surveys. These 4D seismic techniques identified locations of remaining oil in Cainan oil field in Xinjiang Province. An irregular drilling pattern was introduced that increased daily production by 40%. In 2008, two 7-km2 surveys were done at Huanxiling oil field in Liaohe using 6.25 m×6.25 m surface elements and VSP data acquired in two wells. A differential analysis of seismic attributes and a specialized visualization technique showed physical properties of the reservoir and identified fluid distributions so locations of remaining oil could be defined. The objective of this project was to use high-density 3D seismic technology in the secondary recovery stage of the field to find 5×107 tons of remaining oil in Shuguang oil field and to implement a dynamic monitoring technique suitable for heavy oil reservoirs occurring in non-marine sediments across China.
2.1.3
2.2 Successful developments of seismic acquisition, processing, and interpretation software
Full digital seismic technology
Full digital seismic production in CNPC started in 2004. High-resolution of low impedance-contrast zones and development of methods for broad-frequency recording, noise reduction, and improved data processing have combined to produce improved signal data. One example of these strategies being successfully applied is the full-digital data acquired with 5-m line intervals across the Chepaizi area of Junggar. These data revealed the spatial distributions of thin-bed sands in the last series of the Shawan group and reduced drilling risk. Quantitative analysis showed that the dominant frequency of digital data increased 30 Hz, 20 Hz, and 15 Hz for deep, intermediate, and shallow intervals, respectively, compared to the dominant frequencies of analog data. Digital data have provided higher geologic resolution and much better characterization of faults and lithological traps[4]. 2.1.4
Time migrated 4D seismic technology
CNPC has carried out 4D seismic experiments across Xinjiang, Liaohe, Daqing, and Jidong oil fields. This program has included feasibility studies, dual-acquisition consistency analysis, and development of data-processing techniques that ensure equivalent seismic properties are preserved in repeated
2.2.1
KlSeis seismic acquisition engineering software
CNPC began software development in 1998 to reduce the demands for importing technologies and to strengthen the company’s ability to address specific operational challenges. Software system KlSeis was released in 2000 and has now been updated to version 4.0. Important modules deal with acquisition design, forward modeling, static corrections, and quality control. These modules can be applied to a wide variety of seismic acquisition efforts, including P-wave, multiwave, VSP, and streamer projects. An English version of the software was released in 2002 for applications in overseas areas such as the Middle East, Central Asia, and Africa. This decision has resulted in both economic and social benefits, improved CNPC’s competiveness in international markets, and boosted CNPC’s stature as a service provider. 2.2.2 GeoMountain acquisition, processing, and interpretation software CNPC initiated the development of its GeoMountain software to benefit from the company’s many years of seismic
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experience in complex mountainous terrains. GeoMountain version 1.0 is now released. This software focuses on a wide variety of seismic data acquisition, processing, interpretation, and multi-wave applications. Featured technologies include: Forward modeling and target illumination analysis for mountainous terrains, Near-surface modeling, static corrections, and noise removal specialized for mountainous areas, Interpretation analysis that allows reverse fault mapping, fracture prediction, and identification of flow units, and Specialized modules that allow multi-component static corrections, prestack inversion, and joint inversion of P and S data. 2.2.3 GeoEast seismic data processing and interpretation integrated software CNPC began research to develop large-scale seismic data processing and interpretation in 2003 to improve the company’s competency in fundamental seismic operations and to minimize dependence on imported software. GeoEast version 1.0 was released in 2005. Over the next three years, numerous functions were added, algorithms were upgraded, and GeoEast version 2.0 is now available. Offshore, multi-wave, and VSP functions were added to the processing module, and post-stack inversion and reservoir prediction capabilities were added to the interpretation module. The interpretation performance of the software is equivalent to that provided by international software vendors and has unique features of value to CNPC. The development of GeoEast software has provided CNPC valuable intellectual property, allowed competitive advantages of foreign geophysical software to be overcome, provided economic benefits, and improved CNPC’s competiveness in the international seismic contractor market.
Fig. 7
2.3 Successful developments of seismic acquisition equipment 2.3.1
Large-scale seismic acquisition system
In 2006, CNPC launched a project, “Development of Novel Seismic Data Acquisition and Recording System”. Design objectives were achieved in 2008. The CNPC system offers a high-speed data transmission of 40 megabits/s, compared to 16 megabits/s for the Sercel 428 and 8 megabits/s for ION’s System IV. Software development and 60-channel prototype tests were finished in May 2008. Field tests and pilot operations of a 2000-channel system were done in February 2009. Data quality is equivalent to that of systems available from international manufacturers. A comparison of the CNPC system and ION’s Aries technology is shown as Figure 7. The commercialization plan is to manufacture a 20 000-channel system having a 2 ms sample rate in 2010. Manufacture of large-scale seismic systems will reduce the cost of purchasing from foreign providers, increase CNPC’s competitive strength, and build CNPC’s image as a reliable developer of critical technology. 2.3.2
Heavy-duty vibrator
CNPC regards the development of seismic vibrators, shot-hole drilling rigs, swamp equipment, and explosive shooting boxes as important components of its equipment development plans. KZ-28 articulated vibrators and KZ-30 tracked and wheeled vibrators have been developed to satisfy seismic source demands in difficult conditions such as rough topography, deserts, soft-ground terrains, and winter operations. The KZ-34 heavy-duty vibrator uses an innovative guide-pin hydraulic oil lubrication structure, a high-low leather bag accumulator, and a chassis with hinge-type steering gear that transmits more energy into the ground. Fewer vibrators are needed to do proper imaging, and data quality is
Comparison between seismic profiles acquired from same lines with self-developed large-size tools and Aries tools
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improved. These features have resulted in three patents related to the KZ-34 vibrator. Several KZ-28, KZ-30, and KZ-34 vibrators are in operational use. 2.3.3
Seismic drilling rig and carrier
Drilling rigs capable of drilling 80-m holes have been developed for use in mountainous, swampy, and desert terrains. ZCF-06, ZCF-08, and ZCF-32 caterpillar-tracked floating carriers, ZCL-12 wheeled swamp vehicles, and ZJL-01 light-duty hinge-type swamp vehicles have been developed to work in intertidal zones.
3
Challenges to geophysical technology
To meet the demands of oil and gas development required for the national economy, CNPC has proposed four projects for the last three years of the “11th five-year plan”, and these programs should also extend across the period of the “12th five-year plan”. These programs are: Reserve plateau project, Secondary development project, Natural gas grand development project, and Overseas project. With slight variations in focus, these four projects cover the entire CNPC E&P business operation. Geological objectives in these projects will concentrate on complex steep-dip structures, stratigraphic traps, deep carbonate rocks, deep igneous rocks, and secondary development of existing oil fields. There will be many geophysical challenges over the lifetime of these projects. 3.1
Complex steep-dip structures
Complex steep-dip structures occur in the Kuqa and southwestern areas of the Tarim Basin, along the southern edge of the Junggar Basin, in the Dabashan portion of Sichuan, the mountain front of Logmen Mountain, the west wing of the Ordos Basin, northern part of Qaidam, the Kulong Mountain area of Yumen, and other places in the Middle East, South America, and Africa that are of interest to CNPC. These areas are key components of the strategy to “stabilize the west and boost overseas business”. Major problems that have to be overcome involve complex topography, large variations in elevation, complicated lithologies, and low-impedance intervals. Also subsurface structures are complex, with issues being sub-salt tectonics, reverse structures, and strike-slip faults that combine to make seismic wave propagation difficult to manage. Even though technical studies have been done for several years, seismic profiles and geological models often do not match well. The challenges are to improve the resolution of seismic images (the goal being 100 m of tectonic resolution), enhance the imaging of high-dip structure associated with overthrust faults (the goal being to increase the success rate of correct structural interpretation by 20%), and confirm proper structure for development purposes (the goal being to shorten the time of the exploration phase by 20% to 40%).
3.2
Complex topography and stratigraphic traps
Stratigraphically trapped reserves occur in shallow and intermediate depth formations in Bohai Bay, and portions of the Songliao, Ordos, Tarim, Junggar, Tuha, Qaidam, Sanhu, and Sichuan Basins, as well as in other areas of Central Asia, Asia Pacific, and Africa. Operations in these areas are essential for reserve growth. Problems that have to be overcome are thick surface layers of sand and loess, thick weathered zones, complex and heterogenous sedimentation patterns, and thin reservoirs with low porosity, low permeability, and complex gas-water relationships[5–7]. High-resolution seismic data cannot identify individual reservoirs thinner than 3 m. The geophysical challenge is to increase the dominant frequency of seismic data by 10 Hz in western areas of China and by 10 to 15 Hz in eastern areas, with the objective of increasing the drilling success of stratigraphic traps by 20%. 3.3
Imaging deep carbonate and igneous rocks
Carbonate and igneous rocks are the future of natural gas development in China. Carbonate rocks are distributed across Tarim, Sichuan, and Ordos Basins, Bohai Bay, southern China, central Asia, Asia Pacific, and the Middle East. The difficulties associated with carbonates are that reservoirs are deep and heterogeneous. In some case, carbonate structures are below salt, which makes imaging difficult, and in other cases it is essential to define distributions of fractures and karsted cavities. Petrophysical predictions of oil in place are difficult because of complex relationships among water, gas, and oil in carbonates[8]. Geophysical challenges are to improve seismic resolution to the range of 15 to 30 m, with an 80% success rate for predicting carbonate reservoirs of this size, to quantify fractures and cavities, and to create a 10 to 20% increase in successful E&P projects. Igneous rocks are found in deep formations across the Songliao and Junggar Basins, Bohai Bay, and a few other locations. Major problems that affect exploration of igneous rocks are their great depth of burial, their associated complex tectonic forms that make imaging difficult, poor signal-to-noise ratios of deep seismic data, inadequate resolution, and low prediction success of reservoir conditions and hydrocarbon occurrence[9]. Technical challenges are to increase the signal-to-noise ratio of deep reflections by 50%, enhance reservoir resolution to 15 to 30 m with an 80% prediction accuracy, and raise the E&P success rate by 10 to 20%. 3.4
Geophysical challenges of old fields
The term “old fields” refers to areas of Bohai Bay, the Daqing Changyuan area of the Songliao Basin, the northwest part of the Junggar Basin, and the southwest portion of the Qaidam Basin. To assist the operation of old fields, it is essential to perform reservoir characterization, define isolated reservoir compartments, and locate stratigraphic traps and new producing strata. Problems that have to be resolved are detecting individual thin beds, understanding how thin sand and
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shale units are meshed together in complex patterns, locating narrow channels with widths of 300 to 600 m, predicting rock properties in conditions of low porosity and permeability, detecting faults with small vertical throws, and overcoming the limitations of low signal-to-noise and low-resolution deep data. It will be necessary to define targets that are less than 3 m thick and only a few tens of meters wide. These thin, heterogeneous targets are difficult to define for horizontal-well and multi-well drilling programs. Technical challenges are to predict traps only 1 to 3 m thick in the east and 3 to 7 m thick in the west, detect faults with throws of only 3 to 5 m in the east and 5 to 10 m in the west, and establish reservoir modeling that will result in efficient secondary development.
4
Direction for geophysical development
CNPC is confronted with monumental difficulties such as complex mountainous areas, large regions covered by loess tablelands, reservoirs with super-low porosities and permeabilities, and thin-bed targets. Geophysical technology is challenged in every sector of E&P[10]. To meet these challenges, CNPC has formulated a geophysical technology development blueprint (Fig. 8) that provides paths for developing 2D and 3D descriptions, 3D visualization, and 4D monitoring of reservoir systems. In support of exploration, attention will focus on gravity, magnetic, and electrical technologies, seismic acquisition in complex-surface areas, prestack depth migration, and prestack reservoir prediction and trap
Fig. 8
evaluation. Seismic technology will dominate the evaluation phase, with emphasis placed on more accurate 3D seismic and prestack seismic property descriptions, fluid identification, qualitative and semi-quantitative trap evaluation, and reservoir modeling. For the development phase, priorities will be placed on digital seismic, high-density seismic, multi-wave, borehole seismic, 4D seismic, fluid identification, and dynamic reservoir modeling. Integrated seismic, well logging, and drilling engineering will be integrated in a 4D style to support secondary development. Continuous improvements in geophysical software and hardware will occur to ensure a smooth implementation of CNPC’s “Four Great Projects” and co-development of onshore and offshore prospects. CNPC has established four general objectives for technology development. In terms of challenges, these objectives are: Stratigraphic traps: Increase the fundamental frequency of seismic data by 5 to 10 Hz and achieve prediction accuracies of target thicknesses of 1 to 3 m in the east and 3 to 7 m in the west. Complex mountainous areas: Improve seismic imaging accuracy to 100 m and shorten the exploration cycle by 20 to 40%. Reservoir identification and prediction: Predict reservoirs with an accuracy of 15 to 30 m with a prediction success of 80% or more, and improve E&P success in predicting carbonate and igeneous reservoirs by 10 to 20%.
Blueprint of geophysical technology development for CNPC
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Old fields and secondary development: Identify faults and structures having vertical reliefs of 3 to 5 m in the east and 5 to 10 m in the west, with prediction successes of 80% and 70%, respectively, in the east and west, and implement dynamic reservoir monitoring. To achieve these objectives and to address these challenges, CNPC has defined several directions in which technology improvements will occur in core software and hardware efforts and in new geophysical methods. Core development of geophysical equipment and software 10 000-channel data acquisition system Digital geophone Electro-magnetic vibrator Onshore 3D electrical-magnetic system Deep-water exploration equipment Seismic acquisition design and quality control software Seismic processing and interpretation software Special software for reservoir prediction and fluid monitoring Software for geochemical and non-seismic acquisition, processing, and interpretation New geophysical methods Petrophysical analysis technques Petrophysical characterization of heterogeneous reservoirs Anisotropic velocity modeling and imaging technologies for complex structures High-density seismic exploration Multi-wave and multi-component exploration techniques Time migration algorithms Well-to-field joint exploration Deep water streamer and OBC exploration technologies Offshore electromagnetic technology Coal bed methane geophysical technologies Micro-seismic monitoring capability A successful execution of this blueprint plan will result in continuous expansion of CNPC geophysical technologies and services. A fundamental intent is to extend capabilities and services across a wider spectrum of several areas, ranging from structural traps to depositional traps, poststack to prestack, time domain to depth domain, qualitative to quantitative descriptions, reservoir prediction to hydrocarbon monitoring, and post-event to pre-event analysis. Additional goals are to extend the CNPC technical chain from exploration to development so as to span the entire life cycle of oilfields, and to expand CNPC’s business chain across multiple fields such as reservoir, offshore, software, hardware, and information. In the services sector, objectives
are to change the CNPC service pattern from a singular focus to integrated packages in which CNPC will offer company and contractor services ranging from exploration design and reservoir description to well placement and reserves reports, expand the CNPC service market from home to abroad, and shift from domestic markets to high-end markets that serve international major oil companies.
5
Conclusions
By implementing integrated scientific and technical programs, emphasizing new technology applications and research, and strengthening technology transfer, CNPC will develop geophysical technologies that can be applied to foreland fault areas, stratigraphic traps, and carbonate and igneous rocks. High-density seismic, multi-wave, time-migration seismic, borehole seismic, and reservoir geophysics will be developed that will allow reservoir identification to be improved from the 10 to 15 m thickness range to the 1 to 3 m range, improve operational success from 60% to 70%, and remove bottlenecks in E&P projects. To strengthen the development of core software and equipment, the following objectives must be achieved by the end of the “12th five-year plan”: 1. a reservoir-oriented integrated software system based on GeoEast, 2. internal seismic equipment that meets high technical and economic standards and can be commercialized, 3. more than 90% of the home market for vibrators, 4. ownership of 8 to 10 streamer ships, 5. design techniques for streamer deployment and retrieval, 6. trial production of streamers, and 7. know-how related to deep water towing, OBC and electromagnetic operation. By promoting proven technologies, tackling bottlenecks, keeping abreast of emerging technologies, and development of hardware and software systems, CNPC geophysical technology will improve, and will steer the upstream business toward emphasis on seismic technologies that will reduce exploration cost by using fewer wells to achieve greater value and higher efficiency.
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