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Necessity and feasibility of PetroChina mature field redevelopment
PETROLEUM EXPLORATION AND DEVELOPMENT Volume 35, Issue 1, February 2008 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2008, 35(1):1–5.
RESEARCH PAPER
Necessity and feasibility of PetroChina mature field redevelopment HU Wen-rui* PetroChina Company Limited, Beijing 100011, China
Abstract: This paper presents a new concept of redevelopment of mature oilfields and defines its object on the basis of the PetroChina’s oilfield development status analysis, including development stage, remaining reserves, surface engineering, and average oil recovery factor. For mature oilfield redevelopment, three conditions must be met. Firstly, the oilfield producing is over 20 years (heavy oil fields over 12 years); secondly, the recovery factor of recoverable reserves is up to 70%; thirdly, the oilfield water cut is up to 85%. PetroChina has developed special technologies and technical know-how in reservoir study, drilling and production engineering, and surface engineering since the national 11th five-year plan. Mature oilfield redevelopment is complex system engineering and should follow three principles, which are integrative deployment, staged implementation, and pilot study first. Redevelopment of mature oilfields is a necessary way and the expected increase of oil recovery factor ranges from 10% to 20%. Key words: PetroChina; mature oilfields; redevelopment
During the past 50 years, the oilfields which belong to PetroChina Company Limited (PetroChina), have provided a large amount of oil and gas for China, that has contributed significantly to the national economy development and energy security. However, as a large amount of oil and gas were produced, oilfields have got older day by day, mature oilfields are more and more, tertiary oil recovery are limited and the cost is high, the oilfield development is getting more difficult. Currently, 70% of PetroChina’s oil production still comes from the mature oilfields, and the remained recoverable reserves are still considerable, the potential of mature oilfields is extremely huge. Therefore, redevelopment engineering of the mature oilfields is an inevitable choice of PetroChina.
1
Development status of PetroChina
After oil and gas fields were developed for many years, PetroChina’s mature oilfields currently have the common features as follows. These mature oilfields have stepped into the “two-high” stage, which is the stage of high recovery and high water-cut. In the eastern mature oilfields of China, oil production tends to decline, but PetroChina’s oil production keeps stable slightly. By the end of 2006, the recovery of recoverable reserve reached 73.9% and the average water-cut was as high
as 84.9%, it became more difficult to produce. The company’s oil production was 106.53×106 tons in 2006, 79% of which came from the mature oilfields developed over 20 years. The average oil production increased by 0.634×106 tons annually since recent five years; whereas, the production reduced 1.2×106 tons annually in the eastern area, which was mainly located by mature oilfields. Resource condition to keep oil production stable becomes poor in mature oilfields. It is more and more difficult to keep oil production increasing, because the increased recoverable reserve decreases in mature oilfields year by year. Compared to new oilfields, the newly constructed productivity in the mature oilfields dropped from 56% of the ninth five-year plan to 39% of the tenth five-year plan. After the long-term working, the safety and efficiency of the system of the mature oilfields get worse. There are 263 developed oilfields, and 114 of which are over 20 years, accounting for 60% of the total developed reserves. Proportion of the damaged casing wells is increasing gradually, and the recoverable reserve loss increases. Meanwhile, the high energy-consuming and low efficiency of surface system urge to increase investment to reconstruct the oilfields and to deal with the hidden dangers in security and environmental protection.
Received date: 13 November 2007. * Corresponding author. E-mail: [email protected] Copyright © 2008, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
The average oil recovery between PetroChina and international oil company has difference, which still means the big potential. By the end of 2006, PetroChina’s developed OOIP is up to 13×109 tons, and the recoverable reserve is 4.38×109 tons. Except for the Changyuan area of Daqing oilfield, the average recovery is just 25.5%, which is less than the international average level, 35%. Enhancing oil recovery still has big potential.
2 2.1
Conception and foundation of redevelopment Conception of redevelopment
When an oilfield with primary development reached ultimate condition or accorded with abandoned standard, it can be redeveloped using new ideas; reconstructing new development system; applying new secondary producing technology to make oilfield development under safety, environmental protection, energy saving and high efficiency, and finally enhancing the ultimate recovery greatly. This process is called mature oilfield redevelopment [1-6]. For mature oilfield redevelopment, all the three important characteristics must be met: first, the oilfield development and production exceeded 20 years (more than 12 years for heavy oilfield); second, the recovery factor of recoverable reserve is above 70%; third, the oilfield average water cut is up to 85%. 2.2
Foundation of redevelopment
Due to that, the new discovery of reserve is decreasing and development cost is increasing, many foreign oil companies are beginning to switch their attention to mature oilfields. EOR of mature oilfield has been regarded by major international petroleum corporations of ExxonMobil, BP and Shell as the most important development strategy. They have put two-thirds of capital expenditure into development and adjustment of mature oilfields for over three decades. The advanced secondary recovery technologies, including dynamic reservoir description, digital reservoir, water alternative gas (WAG) and multidisciplinary integration, increase the value of mature oilfields continually and reach a purpose of EOR/IOR [7-12]. For example, Miller oilfield of BP Corporation, its present waterflooding recovery has reached 60%, and the recovery is predicated up to 70% after the implementation of CO2 flooding. Also, Romashkino oilfield of Russian, secondary recovery has reached 60% for the Devonian reservoir, Stafjord and Gullfaks oilfields of Statoil, expected recovery will be up to 68% [13] and 65%, respectively. PetroChina’s mature oilfields have passed through splendid history for over 50 years, accumulated abundant technologies, and rich management experiences. PetroChina has reinforced technical research and pilot test on mature oilfields since the corporation put on the market. Currently, in the world, its
waterflooding technology of sandstone oilfields has reached advanced level; polymer flooding technology has ranked leading level; thermal recovery technology of deep heavy oil reservoirs has stepped into advanced ranks, the matching technology of low permeability oilfields’ development has been the leading edge. In the redevelopment of the Liaohe, Yumen, Jilin and Karamay oilfields, not only oil production had kept a stable growth, but also special oilfield development matching technologies have been used in the reservoir geology, drilling and producing technologies and surface system since the eleventh five-year plan performed. These achievements have gradually formed the foundation of redevelopment in theory, technology, and practice [14-16]. 2.2.1
Development of high water cut period
Although many oilfields have stepped into two-high period, the high water cut period and high recovery period, they still make great contribution to oil production and reserve. In fact, about 79% of the PetroChina’s oil production comes from mature oilfields with the two-high, whose remaining recoverable reserve accounting for 73% of the total reserve. Based on the practice of production, about 50% to 70% recoverable reserve in east oilfields of China will be produced in the high water cut period or extra high water cut period. 2.2.2
Improving waterflooding recovery
PetroChina’s expected recovery is 33.6%, with average water displacement efficiency of 56% and average sweep efficiency of 60%. The main affecting factors of displacement efficiency include oil water viscosity ratio, pore structure, and wettability. Usually, the change of the water displacement efficiency is not big, but currently a large number of actual data show that displacement efficiency increases along with the pore volumes of multiple increase of water injection. When the water cut was 84% in well Dongjian 3, an inspective well of Dagang oilfield in 1982, the water displacement efficiency was 57%. When the water cut was up to 92% in well Dongjian 5, another inspective well in the same formation in 2004, the water displacement efficiency reached 76%. It has been proved that waterflooding displacement efficiency can reach between 60% and 80%. The sweep efficiency’s main affecting factors include horizontal plane heterogeneity and inter-layer heterogeneity of reservoir, oil water mobility ratio, perfect degree of injectors and producers, well pattern, injection-production technologies, and so on. Statistics indicate that the present average sweep efficiency of PetroChina’s mature oilfields is about 60%, which can be further improved by means of horizontal well injection-production and some other technologies. Therefore, the ultimate recovery still has great potential space to enhance.
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
2.2.3
Special matching technologies
Since the eleventh five-year plan used, PetroChina has developed a series of special matching technologies, including reservoir geology, drilling and producing technologies, and surface system. 2.2.3.1
Reservoir description and digital reservoir
PetroChina, by integrating seismic data, drilling data, logging data, dynamic monitoring data and producing data and with the aid of the platform of computer and professional software, has conducted the study of large-scale detailed reservoir description after 2004, covering 8.1 billion tons of OOIP; it takes up 62% of the developed reserve, and provided digital reservoir models accordingly. 2.2.3.2
SAGD and steam flooding
SAGD technology in Liaohe oilfield is used with the manner of vertical well combined horizontal well, and it has formed matching technologies, including physical simulation, numerical simulation, drilling and well completion, high quality steam injection and allocation measurement, high volume artificial lift device, performance parameters monitoring and controlling, and real time data acquisition. Steam flooding has formed matching technologies, including optimizing design and adjustment of reservoir engineering, reservoir damage control, separate zone steam injection, high temperature testing, processing of produced fluid at high temperature [17]. SAGD and steam flooding matching technologies have obtained great success in Liaohe oilfield [18], and many technologies have original innovation according to the well depth only. Liaohe oilfield has kept stable production by applying SAGD, steam flooding and horizontal wells. Qi-40 block in Liaohe oilfield entirely turns to steam flooding development, and the oil recovery could be increased by 23.7%. Huff and puff with steam flooding, the ultimate oil recovery is up to 50%. The oil recovery in Shu-1block should increase by 30% after entirely turning huff and puff to SAGD and the ultimate oil recovery is about 52.8% after applying huff and puff and SAGD. 2.2.3.3
Horizontal well technology
Many different types of horizontal well have been used, including traditional horizontal well, sidetrack well, fishbone well, multilateral well, multi-branch well, step horizontal well etc. The horizontal well matching technologies, including geology designs, engineering design (trajectory control), reservoir damage control (zero pollution completion fluid), artificial lift, production monitoring and surveillance, measurement instrument and device, were initially formed. All these technologies above cover different types of reservoir including heavy oil reservoir, bottom water and edge water
reservoir, thin zone reservoir, low permeability reservoir, fracture reservoir, and so on. At present, more than 1 000 horizontal wells can be drilled per year. Horizontal well technologies have a great development in the Liaohe, Xinjiang and Jidong oilfields, which will become a model in the spread of horizontal well technologies [19]. Xinhai-27 of Liaohe oilfield, Miaoqian of Jidong oilfield, Zaobei of Dagang oilfield and Jing-11 of Huabei oilfield use horizontal wells for redevelopment, and 112 horizontal wells and 31 sidetrack wells are designed. It is predicted that the water flooding recovery will increase by 7%. This puts forward the direction for further increasing oil recovery of high water cut oilfields, low oil rate oilfields, and high oil recovery oilfields. 2.2.3.4
Optimization and simplification of surface system
Optimization and simplification is to optimize surface system of new oilfield and to simply surface system of mature oilfield. One-stage station processing, closed transportation at normal temperature, online measure of individual well, automatic control and so on, are developed and formed, which are all used to save energy, reduce consumption, and improve the efficiency. Surface engineering technologies appropriate for mature oilfield development have generally been formed. Dagang oilfield has realized online measurement of the individual well, which becomes the base of optimizing and simplifying technologies, and constructing digital oilfield. Xinjiang oilfield uses two-phase flow metering of individual well and cancels the measure station to realize one and half stage station processing. After rebuilding of gather and transportation system in Gangxi of Dagang oilfield, energy consumption per ton oil decreases from 2040 MJ to 1830 MJ, and the surface system efficiency rises from 45.8% to 56.2%. Xifeng of Changqing oilfield, Lamadian of Daqing oilfield and Xinglongtai of Liaohe oilfield also have accumulated precious experience of optimization and simplification. 2.2.4
Preliminary application
Besides the reservoir geology features and fluid properties, the oil recovery is also related to the degree of reservoir recognition and technology application. During recent years, with the rapid development of petroleum science and technology, there was considerable progress both in the measure of reservoir recognition and the level of development technology, which made it better suit reservoir features and the change of oil and water contact. In this way, we can exploit the potential of mature oilfield effectively and further increase the oil recovery. Integrated adjustment of Fuyu, Jilin oilfield shows good results. The oilfield has been developed for over 40 years. At present, because of four problems of imperfect well pattern,
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
poor well condition, poor water injection condition, and unconformable surface system, the annual production decreased from 1.027 million tons in 1984 to 0.65 million tons in 2003. Through acquiring 3D seismic data and conducting detailed reservoir description, adjusting well pattern and improving injecting-producing relationship, enhancing water injection, improving dynamic water allocation to injector, performing water shutoff and injecting profile control, using one and half or two stage station processing, and transporting at normal temperature, the annual production reached 1.0 million tons and the recovery rose by 5% to 8%. Meanwhile, the energy consumption per ton decreased from 4 029 MJ to 1 548 MJ. In a word, redevelopment made rejuvenation of Jilin oilfield. The recovery of some high-degree water-flooding blocks has already been over 50%, which proved that redevelopment has huge potential to increase oil recovery. Karamay of Xinjiang oilfield has been developed over 50 years; with the idea of redevelopment, by reconstructing reservoir model of mature oilfield at the north-west marginal area of Zungel basin, and perfecting well pattern, and so on, the annual production of the mature oilfield can reach to 4.0 million tons. The redevelopment will turn the decline trend, and rise oil recovery by 8%.
3
Technical ideas of redevelopment
Mature oilfield redevelopment is a complex system engineering, the cores of which are advancing reservoir management and new secondary recovery technology. Technical ideas of mature oilfield redevelopment were expressed as three new aspects, including reconstructing new geological system, rearranging new well pattern, and rebuilding surface process system. However, new secondary recovery technology is integrated application and development of the conventional secondary recovery techniques, and it locates between secondary and tertiary recovery. 3.1
Reconstructing geological system/model
Not only were the high resolution 3D seismic, high precision dynamic monitoring and detailed reservoir description used, but also old data and worthless information were abandoned to improve decision-making of mature oilfield redevelopment. Recognizing reservoir again, making clear remained oil distribution, storing and accessing data automatically, development planning generating automatically, building digital oilfield, with these measure, supervising and controlling on real time and automatically can be achieved. 3.2
Rearranging well pattern
Traditional vertical well type and pattern should been
changed into advanced well types, which are cluster well, horizontal well, multi-branch well, multilateral well and pad horizontal well. New well patterns should be deployed, a large number of old wells of the higher intervention cost should be abandoned, especially whose intervention cost is more than oil sale income according to wellbore condition, therefore, new well pattern of mature oilfield redevelopment should be completed thoroughly. To improve injection and production system and waterflooding efficiency, infill and adjustment of well pattern were implemented. 3.3
Rebuilding surface process system
According to the development characteristics of high water cut oilfields, the surface process system should be simplified and optimized under the new well pattern, based on cluster drilling and pad well. The gather and transportation station of the one stage or one and half stage will be used; their features are short flow, normal temperature transportation, expanding cool transportation radius, transportation through pump to pump. The facilities of the high-energy consumption and low efficiency should be stopped to realize four targets, which are four-new, three-high, three-all and one-cycle. That the surface facilities run at the climate of low energy consumption, low cost, and high automatization, will be realized. “Four-new” refers to the application of new material, new process and new technology, and new equipment in the redevelopment of mature oilfields. “Three-high” means that high-energy consumption, low efficiency equipments should be replaced by high-efficiency heating furnace, high-efficiency pump and high-efficiency transfer pump. “Three-all” refers to meet environmental requirements, all pipelines should be closed, and all exhaust, production water should be processed and all those should be reused reasonably. “One-cycle” refers to that oilfield produce safely and environmentally to achieve the “recycling economy”.
4 4.1
Objective and deployment of redevelopment Objective
By the end of 2006, the total proven reserve of PetroChina is 16.7 billion tons, while the developed reserve is 13 billion tons. The cumulative oil production is 3.24 billion tons and the recoverable reserve is 4.38 billion tons. The average recovery of PetroChina is 33.6%. An amount of research and practice show that the current recovery has a potential increment between 10% and 20%. If present recovery of 34% is a reference value, target oil recovery of redevelopment for common oilfield will increase up to 44% to 49%, and for oilfield of high permeability and other special reservoir to 50% to 55%. On the current situation, the ultimate oil
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
recovery of 50% can be achieved. For some oilfields with better conditions, the recovery increment will be larger. 4.2
Important deployment
Redevelopment is a new system project, and its object has very complex distribution of the remaining oil, which is highly scattered in the oilfield and relatively abundant locally, and has a complex water oil contact. The optimization and control of well trajectory is considerably difficult. And the drilling technology is complex. To maintain stable oil production is also hard. There is a certain degree of technical and economical risks because the new system establishment and old system adjustment, the lump-sum investment will be large. To minimize the technical and economical risks of redevelopment, the three principles should be complied, “integrative deployment, staged implementation, pilot study first”. First of all, three technology demonstration projects for different types of reservoir should be implemented; five key research projects and six pilot projects should be smoothly organized; at the same time, six major development tests should be performed. These activities ensure that the redevelopment is highly efficient and orderly, and great effectiveness and benefit can be achieved eventually. Three technology demonstration projects are the new 3D seismic technology in Changyuan, Daqing oilfield, multidisciplinary integration of geological research technology in Daqing, and integrated optimization technology of the onshore surface system in Nanbu, Jidong oilfield. Five key research projects refer to a new template for locating precisely the remaining oil, data input and development planning generating automatically for the digital oilfield, injecting-producing matching technology, the new method of calculating recovery and the new surface process technology. Carrying out these five key researches will help to overcome the technology difficulties and give technical support for the redevelopment’s going. Six pilot projects are development model conversion for heavy oil production of Liaohe oilfield, development of sandstone reservoir in the northwest marginal of Karamay oilfield and development of onshore complex fault-block reservoir of Nanbu, Jidong oilfield, development of low-permeability reservoir of both Laojunmiao and Ya’erxia, Yumen oilfield, the development of middle-to-high permeability reservoir of the western Dagang oilfield, and development of low permeability reservoir of Fuyu, Jilin oilfield. These six projects will increase oil recovery by 9.8%. Six major development tests refer to the redevelopment, which increased oil recovery of Changyuan, Daqing oilfield after tertiary oil recovery, the steam flooding / SAGD for developing heavy oil reservoir II and III of Liaohe oilfield, recycling economy model of Nanbu onshore, Jidong oilfield, CO2 EOR of the extra-low permeability of Daqing and Jilin oilfield, EOR project of both Laojunmiao and Ya’erxia,
Yumen oilfield. Through these six major development tests, EOR methods and development models of different type reservoirs will be explored and validated, and matching technologies will also be developed, it will put forward the direction for other mature oilfields’ redevelopment. A series of technological breakthroughs have been achieved, since these six tests performed, promoting mature oilfield redevelopment greatly.
5
Conclusions
Experimental research in laboratory and oilfield test have shown that the mature oilfields still have huge potential, and the oil recovery of PetroChina has the space of being enhanced by 10% to 20%. The main technical line of mature oilfield redevelopment are reconstructing geological system/model, rearranging well pattern and rebuilding surface process system. Redevelopment is difficult and complex system engineering and should follow three principles, which are integrative deployment, staged implementation, and pilot first. Redevelopment should be efficiently and orderly performed to reduce economic and technical risks and enhance beneficial effect of oilfield development. To sum up, the redevelopment potential of PetroChina’s mature oilfields is huge, the current development situation determined that the mature oilfields must be redeveloped; both its prospect and significance are very great; it would completely change the degree of the utilization and the gain of natural resources, and achieve sustainable development of China's oil resources greatly and safeguard the national oil security.
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RESEARCH PAPER
Necessity and feasibility of PetroChina mature field redevelopment HU Wen-rui* PetroChina Company Limited, Beijing 100011, China
Abstract: This paper presents a new concept of redevelopment of mature oilfields and defines its object on the basis of the PetroChina’s oilfield development status analysis, including development stage, remaining reserves, surface engineering, and average oil recovery factor. For mature oilfield redevelopment, three conditions must be met. Firstly, the oilfield producing is over 20 years (heavy oil fields over 12 years); secondly, the recovery factor of recoverable reserves is up to 70%; thirdly, the oilfield water cut is up to 85%. PetroChina has developed special technologies and technical know-how in reservoir study, drilling and production engineering, and surface engineering since the national 11th five-year plan. Mature oilfield redevelopment is complex system engineering and should follow three principles, which are integrative deployment, staged implementation, and pilot study first. Redevelopment of mature oilfields is a necessary way and the expected increase of oil recovery factor ranges from 10% to 20%. Key words: PetroChina; mature oilfields; redevelopment
During the past 50 years, the oilfields which belong to PetroChina Company Limited (PetroChina), have provided a large amount of oil and gas for China, that has contributed significantly to the national economy development and energy security. However, as a large amount of oil and gas were produced, oilfields have got older day by day, mature oilfields are more and more, tertiary oil recovery are limited and the cost is high, the oilfield development is getting more difficult. Currently, 70% of PetroChina’s oil production still comes from the mature oilfields, and the remained recoverable reserves are still considerable, the potential of mature oilfields is extremely huge. Therefore, redevelopment engineering of the mature oilfields is an inevitable choice of PetroChina.
1
Development status of PetroChina
After oil and gas fields were developed for many years, PetroChina’s mature oilfields currently have the common features as follows. These mature oilfields have stepped into the “two-high” stage, which is the stage of high recovery and high water-cut. In the eastern mature oilfields of China, oil production tends to decline, but PetroChina’s oil production keeps stable slightly. By the end of 2006, the recovery of recoverable reserve reached 73.9% and the average water-cut was as high
as 84.9%, it became more difficult to produce. The company’s oil production was 106.53×106 tons in 2006, 79% of which came from the mature oilfields developed over 20 years. The average oil production increased by 0.634×106 tons annually since recent five years; whereas, the production reduced 1.2×106 tons annually in the eastern area, which was mainly located by mature oilfields. Resource condition to keep oil production stable becomes poor in mature oilfields. It is more and more difficult to keep oil production increasing, because the increased recoverable reserve decreases in mature oilfields year by year. Compared to new oilfields, the newly constructed productivity in the mature oilfields dropped from 56% of the ninth five-year plan to 39% of the tenth five-year plan. After the long-term working, the safety and efficiency of the system of the mature oilfields get worse. There are 263 developed oilfields, and 114 of which are over 20 years, accounting for 60% of the total developed reserves. Proportion of the damaged casing wells is increasing gradually, and the recoverable reserve loss increases. Meanwhile, the high energy-consuming and low efficiency of surface system urge to increase investment to reconstruct the oilfields and to deal with the hidden dangers in security and environmental protection.
Received date: 13 November 2007. * Corresponding author. E-mail: [email protected] Copyright © 2008, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
The average oil recovery between PetroChina and international oil company has difference, which still means the big potential. By the end of 2006, PetroChina’s developed OOIP is up to 13×109 tons, and the recoverable reserve is 4.38×109 tons. Except for the Changyuan area of Daqing oilfield, the average recovery is just 25.5%, which is less than the international average level, 35%. Enhancing oil recovery still has big potential.
2 2.1
Conception and foundation of redevelopment Conception of redevelopment
When an oilfield with primary development reached ultimate condition or accorded with abandoned standard, it can be redeveloped using new ideas; reconstructing new development system; applying new secondary producing technology to make oilfield development under safety, environmental protection, energy saving and high efficiency, and finally enhancing the ultimate recovery greatly. This process is called mature oilfield redevelopment [1-6]. For mature oilfield redevelopment, all the three important characteristics must be met: first, the oilfield development and production exceeded 20 years (more than 12 years for heavy oilfield); second, the recovery factor of recoverable reserve is above 70%; third, the oilfield average water cut is up to 85%. 2.2
Foundation of redevelopment
Due to that, the new discovery of reserve is decreasing and development cost is increasing, many foreign oil companies are beginning to switch their attention to mature oilfields. EOR of mature oilfield has been regarded by major international petroleum corporations of ExxonMobil, BP and Shell as the most important development strategy. They have put two-thirds of capital expenditure into development and adjustment of mature oilfields for over three decades. The advanced secondary recovery technologies, including dynamic reservoir description, digital reservoir, water alternative gas (WAG) and multidisciplinary integration, increase the value of mature oilfields continually and reach a purpose of EOR/IOR [7-12]. For example, Miller oilfield of BP Corporation, its present waterflooding recovery has reached 60%, and the recovery is predicated up to 70% after the implementation of CO2 flooding. Also, Romashkino oilfield of Russian, secondary recovery has reached 60% for the Devonian reservoir, Stafjord and Gullfaks oilfields of Statoil, expected recovery will be up to 68% [13] and 65%, respectively. PetroChina’s mature oilfields have passed through splendid history for over 50 years, accumulated abundant technologies, and rich management experiences. PetroChina has reinforced technical research and pilot test on mature oilfields since the corporation put on the market. Currently, in the world, its
waterflooding technology of sandstone oilfields has reached advanced level; polymer flooding technology has ranked leading level; thermal recovery technology of deep heavy oil reservoirs has stepped into advanced ranks, the matching technology of low permeability oilfields’ development has been the leading edge. In the redevelopment of the Liaohe, Yumen, Jilin and Karamay oilfields, not only oil production had kept a stable growth, but also special oilfield development matching technologies have been used in the reservoir geology, drilling and producing technologies and surface system since the eleventh five-year plan performed. These achievements have gradually formed the foundation of redevelopment in theory, technology, and practice [14-16]. 2.2.1
Development of high water cut period
Although many oilfields have stepped into two-high period, the high water cut period and high recovery period, they still make great contribution to oil production and reserve. In fact, about 79% of the PetroChina’s oil production comes from mature oilfields with the two-high, whose remaining recoverable reserve accounting for 73% of the total reserve. Based on the practice of production, about 50% to 70% recoverable reserve in east oilfields of China will be produced in the high water cut period or extra high water cut period. 2.2.2
Improving waterflooding recovery
PetroChina’s expected recovery is 33.6%, with average water displacement efficiency of 56% and average sweep efficiency of 60%. The main affecting factors of displacement efficiency include oil water viscosity ratio, pore structure, and wettability. Usually, the change of the water displacement efficiency is not big, but currently a large number of actual data show that displacement efficiency increases along with the pore volumes of multiple increase of water injection. When the water cut was 84% in well Dongjian 3, an inspective well of Dagang oilfield in 1982, the water displacement efficiency was 57%. When the water cut was up to 92% in well Dongjian 5, another inspective well in the same formation in 2004, the water displacement efficiency reached 76%. It has been proved that waterflooding displacement efficiency can reach between 60% and 80%. The sweep efficiency’s main affecting factors include horizontal plane heterogeneity and inter-layer heterogeneity of reservoir, oil water mobility ratio, perfect degree of injectors and producers, well pattern, injection-production technologies, and so on. Statistics indicate that the present average sweep efficiency of PetroChina’s mature oilfields is about 60%, which can be further improved by means of horizontal well injection-production and some other technologies. Therefore, the ultimate recovery still has great potential space to enhance.
HU Wen-rui / Petroleum Exploration and Development, 2008, 35(1): 1–5
2.2.3
Special matching technologies
Since the eleventh five-year plan used, PetroChina has developed a series of special matching technologies, including reservoir geology, drilling and producing technologies, and surface system. 2.2.3.1
Reservoir description and digital reservoir
PetroChina, by integrating seismic data, drilling data, logging data, dynamic monitoring data and producing data and with the aid of the platform of computer and professional software, has conducted the study of large-scale detailed reservoir description after 2004, covering 8.1 billion tons of OOIP; it takes up 62% of the developed reserve, and provided digital reservoir models accordingly. 2.2.3.2
SAGD and steam flooding
SAGD technology in Liaohe oilfield is used with the manner of vertical well combined horizontal well, and it has formed matching technologies, including physical simulation, numerical simulation, drilling and well completion, high quality steam injection and allocation measurement, high volume artificial lift device, performance parameters monitoring and controlling, and real time data acquisition. Steam flooding has formed matching technologies, including optimizing design and adjustment of reservoir engineering, reservoir damage control, separate zone steam injection, high temperature testing, processing of produced fluid at high temperature [17]. SAGD and steam flooding matching technologies have obtained great success in Liaohe oilfield [18], and many technologies have original innovation according to the well depth only. Liaohe oilfield has kept stable production by applying SAGD, steam flooding and horizontal wells. Qi-40 block in Liaohe oilfield entirely turns to steam flooding development, and the oil recovery could be increased by 23.7%. Huff and puff with steam flooding, the ultimate oil recovery is up to 50%. The oil recovery in Shu-1block should increase by 30% after entirely turning huff and puff to SAGD and the ultimate oil recovery is about 52.8% after applying huff and puff and SAGD. 2.2.3.3
Horizontal well technology
Many different types of horizontal well have been used, including traditional horizontal well, sidetrack well, fishbone well, multilateral well, multi-branch well, step horizontal well etc. The horizontal well matching technologies, including geology designs, engineering design (trajectory control), reservoir damage control (zero pollution completion fluid), artificial lift, production monitoring and surveillance, measurement instrument and device, were initially formed. All these technologies above cover different types of reservoir including heavy oil reservoir, bottom water and edge water
reservoir, thin zone reservoir, low permeability reservoir, fracture reservoir, and so on. At present, more than 1 000 horizontal wells can be drilled per year. Horizontal well technologies have a great development in the Liaohe, Xinjiang and Jidong oilfields, which will become a model in the spread of horizontal well technologies [19]. Xinhai-27 of Liaohe oilfield, Miaoqian of Jidong oilfield, Zaobei of Dagang oilfield and Jing-11 of Huabei oilfield use horizontal wells for redevelopment, and 112 horizontal wells and 31 sidetrack wells are designed. It is predicted that the water flooding recovery will increase by 7%. This puts forward the direction for further increasing oil recovery of high water cut oilfields, low oil rate oilfields, and high oil recovery oilfields. 2.2.3.4
Optimization and simplification of surface system
Optimization and simplification is to optimize surface system of new oilfield and to simply surface system of mature oilfield. One-stage station processing, closed transportation at normal temperature, online measure of individual well, automatic control and so on, are developed and formed, which are all used to save energy, reduce consumption, and improve the efficiency. Surface engineering technologies appropriate for mature oilfield development have generally been formed. Dagang oilfield has realized online measurement of the individual well, which becomes the base of optimizing and simplifying technologies, and constructing digital oilfield. Xinjiang oilfield uses two-phase flow metering of individual well and cancels the measure station to realize one and half stage station processing. After rebuilding of gather and transportation system in Gangxi of Dagang oilfield, energy consumption per ton oil decreases from 2040 MJ to 1830 MJ, and the surface system efficiency rises from 45.8% to 56.2%. Xifeng of Changqing oilfield, Lamadian of Daqing oilfield and Xinglongtai of Liaohe oilfield also have accumulated precious experience of optimization and simplification. 2.2.4
Preliminary application
Besides the reservoir geology features and fluid properties, the oil recovery is also related to the degree of reservoir recognition and technology application. During recent years, with the rapid development of petroleum science and technology, there was considerable progress both in the measure of reservoir recognition and the level of development technology, which made it better suit reservoir features and the change of oil and water contact. In this way, we can exploit the potential of mature oilfield effectively and further increase the oil recovery. Integrated adjustment of Fuyu, Jilin oilfield shows good results. The oilfield has been developed for over 40 years. At present, because of four problems of imperfect well pattern,
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poor well condition, poor water injection condition, and unconformable surface system, the annual production decreased from 1.027 million tons in 1984 to 0.65 million tons in 2003. Through acquiring 3D seismic data and conducting detailed reservoir description, adjusting well pattern and improving injecting-producing relationship, enhancing water injection, improving dynamic water allocation to injector, performing water shutoff and injecting profile control, using one and half or two stage station processing, and transporting at normal temperature, the annual production reached 1.0 million tons and the recovery rose by 5% to 8%. Meanwhile, the energy consumption per ton decreased from 4 029 MJ to 1 548 MJ. In a word, redevelopment made rejuvenation of Jilin oilfield. The recovery of some high-degree water-flooding blocks has already been over 50%, which proved that redevelopment has huge potential to increase oil recovery. Karamay of Xinjiang oilfield has been developed over 50 years; with the idea of redevelopment, by reconstructing reservoir model of mature oilfield at the north-west marginal area of Zungel basin, and perfecting well pattern, and so on, the annual production of the mature oilfield can reach to 4.0 million tons. The redevelopment will turn the decline trend, and rise oil recovery by 8%.
3
Technical ideas of redevelopment
Mature oilfield redevelopment is a complex system engineering, the cores of which are advancing reservoir management and new secondary recovery technology. Technical ideas of mature oilfield redevelopment were expressed as three new aspects, including reconstructing new geological system, rearranging new well pattern, and rebuilding surface process system. However, new secondary recovery technology is integrated application and development of the conventional secondary recovery techniques, and it locates between secondary and tertiary recovery. 3.1
Reconstructing geological system/model
Not only were the high resolution 3D seismic, high precision dynamic monitoring and detailed reservoir description used, but also old data and worthless information were abandoned to improve decision-making of mature oilfield redevelopment. Recognizing reservoir again, making clear remained oil distribution, storing and accessing data automatically, development planning generating automatically, building digital oilfield, with these measure, supervising and controlling on real time and automatically can be achieved. 3.2
Rearranging well pattern
Traditional vertical well type and pattern should been
changed into advanced well types, which are cluster well, horizontal well, multi-branch well, multilateral well and pad horizontal well. New well patterns should be deployed, a large number of old wells of the higher intervention cost should be abandoned, especially whose intervention cost is more than oil sale income according to wellbore condition, therefore, new well pattern of mature oilfield redevelopment should be completed thoroughly. To improve injection and production system and waterflooding efficiency, infill and adjustment of well pattern were implemented. 3.3
Rebuilding surface process system
According to the development characteristics of high water cut oilfields, the surface process system should be simplified and optimized under the new well pattern, based on cluster drilling and pad well. The gather and transportation station of the one stage or one and half stage will be used; their features are short flow, normal temperature transportation, expanding cool transportation radius, transportation through pump to pump. The facilities of the high-energy consumption and low efficiency should be stopped to realize four targets, which are four-new, three-high, three-all and one-cycle. That the surface facilities run at the climate of low energy consumption, low cost, and high automatization, will be realized. “Four-new” refers to the application of new material, new process and new technology, and new equipment in the redevelopment of mature oilfields. “Three-high” means that high-energy consumption, low efficiency equipments should be replaced by high-efficiency heating furnace, high-efficiency pump and high-efficiency transfer pump. “Three-all” refers to meet environmental requirements, all pipelines should be closed, and all exhaust, production water should be processed and all those should be reused reasonably. “One-cycle” refers to that oilfield produce safely and environmentally to achieve the “recycling economy”.
4 4.1
Objective and deployment of redevelopment Objective
By the end of 2006, the total proven reserve of PetroChina is 16.7 billion tons, while the developed reserve is 13 billion tons. The cumulative oil production is 3.24 billion tons and the recoverable reserve is 4.38 billion tons. The average recovery of PetroChina is 33.6%. An amount of research and practice show that the current recovery has a potential increment between 10% and 20%. If present recovery of 34% is a reference value, target oil recovery of redevelopment for common oilfield will increase up to 44% to 49%, and for oilfield of high permeability and other special reservoir to 50% to 55%. On the current situation, the ultimate oil
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recovery of 50% can be achieved. For some oilfields with better conditions, the recovery increment will be larger. 4.2
Important deployment
Redevelopment is a new system project, and its object has very complex distribution of the remaining oil, which is highly scattered in the oilfield and relatively abundant locally, and has a complex water oil contact. The optimization and control of well trajectory is considerably difficult. And the drilling technology is complex. To maintain stable oil production is also hard. There is a certain degree of technical and economical risks because the new system establishment and old system adjustment, the lump-sum investment will be large. To minimize the technical and economical risks of redevelopment, the three principles should be complied, “integrative deployment, staged implementation, pilot study first”. First of all, three technology demonstration projects for different types of reservoir should be implemented; five key research projects and six pilot projects should be smoothly organized; at the same time, six major development tests should be performed. These activities ensure that the redevelopment is highly efficient and orderly, and great effectiveness and benefit can be achieved eventually. Three technology demonstration projects are the new 3D seismic technology in Changyuan, Daqing oilfield, multidisciplinary integration of geological research technology in Daqing, and integrated optimization technology of the onshore surface system in Nanbu, Jidong oilfield. Five key research projects refer to a new template for locating precisely the remaining oil, data input and development planning generating automatically for the digital oilfield, injecting-producing matching technology, the new method of calculating recovery and the new surface process technology. Carrying out these five key researches will help to overcome the technology difficulties and give technical support for the redevelopment’s going. Six pilot projects are development model conversion for heavy oil production of Liaohe oilfield, development of sandstone reservoir in the northwest marginal of Karamay oilfield and development of onshore complex fault-block reservoir of Nanbu, Jidong oilfield, development of low-permeability reservoir of both Laojunmiao and Ya’erxia, Yumen oilfield, the development of middle-to-high permeability reservoir of the western Dagang oilfield, and development of low permeability reservoir of Fuyu, Jilin oilfield. These six projects will increase oil recovery by 9.8%. Six major development tests refer to the redevelopment, which increased oil recovery of Changyuan, Daqing oilfield after tertiary oil recovery, the steam flooding / SAGD for developing heavy oil reservoir II and III of Liaohe oilfield, recycling economy model of Nanbu onshore, Jidong oilfield, CO2 EOR of the extra-low permeability of Daqing and Jilin oilfield, EOR project of both Laojunmiao and Ya’erxia,
Yumen oilfield. Through these six major development tests, EOR methods and development models of different type reservoirs will be explored and validated, and matching technologies will also be developed, it will put forward the direction for other mature oilfields’ redevelopment. A series of technological breakthroughs have been achieved, since these six tests performed, promoting mature oilfield redevelopment greatly.
5
Conclusions
Experimental research in laboratory and oilfield test have shown that the mature oilfields still have huge potential, and the oil recovery of PetroChina has the space of being enhanced by 10% to 20%. The main technical line of mature oilfield redevelopment are reconstructing geological system/model, rearranging well pattern and rebuilding surface process system. Redevelopment is difficult and complex system engineering and should follow three principles, which are integrative deployment, staged implementation, and pilot first. Redevelopment should be efficiently and orderly performed to reduce economic and technical risks and enhance beneficial effect of oilfield development. To sum up, the redevelopment potential of PetroChina’s mature oilfields is huge, the current development situation determined that the mature oilfields must be redeveloped; both its prospect and significance are very great; it would completely change the degree of the utilization and the gain of natural resources, and achieve sustainable development of China's oil resources greatly and safeguard the national oil security.
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