Advances on special structure drilling development techniques in Shengli Oilfield

PETROLEUM EXPLORATION AND DEVELOPMENT Volume 35, Issue 3, June 2008 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2008, 35(3): 318–329.

RESEARCH PAPER

Advances on special structure drilling development techniques in Shengli Oilfield ZHOU Ying-jie Geological Scientific Research Institute, SLOF, SINOPEC, Shandong 257015, China

Abstract: Shengli Oilfield has developed the reservoir engineering design and drilling-completion-production techniques of

special structure drilling for reservoirs with bottom water, fault block, heavy oil, unconformity etc, and drilled different types of wells including horizontal well, sidetracked well, extended reach well, multi-lateral horizontal well and so on. There are 586 different horizontal wells in 181 reservoirs of different types, and 742 sidetracked wells in 284 development units. The annual oil production is 1.21 and 0.79 million tons, respectively, and the cumulative oil production 8.25 and 4.09 million tons. The special structure drilling has become one of the dominant techniques for the stable production and production growth of the field. In recent years, new advancements have been achieved in the reservoir description, reservoir engineering design, well drilling technology, well completion technology and producing technology for thin-layer reservoirs, high-cut-water thick-layer positive rhythm reservoirs, buried hill heavy oil reservoirs, extra-heavy oil reservoirs, and complicated fault-block reservoirs. Key words: Shengli Oilfield; special structure well; horizontal well; side-track well; extended reach well; multi-lateral horizontal well; fishbone horizontal well; horizontal well injection

Introduction The special structure well is defined in this article as any type of well except the conventional vertical well, which encompasses four types of lateral, horizontal, extended reach, and branch wells. The special structure well is proven technically and economically to be more advantageous as given below than the vertical well: (1) being feasible in a broad range of reservoirs and increasing recovery of oil and gas, (2) reducing the number of wells and saving the investment, (3) having less leased area and reducing the environmental pressure caused by exploring and producing. Thus, the special structure well has been developed rapidly and used widely for the last two decades[1,2]. Scholars in China have studied the fundamentals in various aspects[3-13] and their applications[14-22] of horizontal wells, and have made great progress, which promotes greatly the development and application of the horizontal well technology in China[23,24]. Shengli Oilfield is one of the oilfields in which the horizontal wells were adopted earliest and technology advance was most rapid in China. The horizontal wells have been introduced to various types of reservoirs, including bottom water reservoir, roof-faulted reservoir, stratigraphic unconformity reservoir, uncompartmentalized and heavy oil reservoirs, and have obtained better production performance and economic benefit

in Shengli Oilfield[25]. In recent years, the special structure well has been adopted to increase the reservoir recovery and economic benefit in more challenging reservoirs, which include thin reservoir, positive rhythm thick reservoir at extra-high water cut stage, buried-hill reservoir with extra-heavy crude oil, super-heavy crude oil reservoir, complex faulted reservoir, and offshore reservoirs, thus widening the domain for the technology of special structural wells.

1

Present situation of special structure well

1.1

Developing history of special structure well

The development of special structure well technology in Shengli Oilfield started in the early 1990s. It experienced solving the key problems and researching in 1991–1995 periods, promoting and rapid application development in the 1996–2000 periods, fine tapping potential and rapid development in the 2001–2005 periods. 1.1.1

Stage of solving the key problems and researching

In 1990, the horizontal well technology was introduced to the Shengli Oilfield to solve the problem of the lower success rate of vertical drilling in the complex reservoirs, which were formed by stratigraphic unconformity as a result of sub-aerial

Received date: 19 March 2007; Revised date: 13 March 2008. * Corresponding author. E-mail: [email protected] Foundation item: A project in Ninth Five Years Plan (95-108-02-01); A SINOPEC project in Tenth Five Years Plan (P01049) Copyright © 2008, Research Institute of Petroleum Exploration and Development, PetroChina. Published by Elsevier BV. All rights reserved.

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

exposure and erosion. The first horizontal well drilled in Shengli Oilfield was Well Chengke 1, for which the total thickness of 19 oil layers encountered was 211.5 m; among these, 17 layers were newly discovered, and the oil test showed that the production rate was 309t/d. It indicated that some reservoirs with high productivity can be discovered by the horizontal well but not by the vertical well. The success in Well Chengke1 reduced the risk and ended the three years difficult dilemma of exploration in this area. Subsequently, four pre-exploration and appraisal wells designed for this area in the coming two years were used to anatomize the stratigraphic unconformity reservoirs in the northeast slope of Chengdong Protuberance. Also, the four wells provided the experiences in geological design, drilling, and production technologies for the horizontal well. To establish the horizontal well matching technology with own intellectual property rights, the national support focused on the project “Research on horizontal well technology for heavy oil reservoirs” in Shengli Oilfield, thus forming a series of mature technologies for horizontal wells, including the arts of geological and reservoir designs, drilling, logging, well completion, and production techniques. In this stage, 31 horizontal wells were put into production in glutenite heavy oil reservoirs in Le’an Oilfield, and obtained obvious production performance, and the oil production was 3.0̢5.7 times that of the vertical well. 1.1.2

Stage of promoting and rapid development

In 1996-2000, the Shengli Oilfield tried best to promote the application of horizontal well and their matching technology. As well, “Research on lateral well and drilling&production matching technology” was carried out under national support. The matching technologies of geological design, drilling, and production of short-radius and casing with ĭ139.7 mm lateral wells were established, which fitted various types of reservoirs in Shengli Oilfield. The oilfield development was successful in this period. A total of 132 horizontal wells were drilled, out of which 11 wells were lateral. Generally, the initial oil rate of individual well averaged 21.1 t/d, which was 2̢3 times that of the adjacent old wells. 224 lateral wells were put into production and the initial oil rate of individual well averaged 14.4t/d. 1.1.3 Stage of fine tapping potential and rapid development The candidate criteria for and the screening method of horizontal and lateral wells in various types of reservoirs were established, based on the research “the application of horizontal and lateral wells technologies” by Shengli Oilfield, under the support of SINOPEC cooperation. The optimum selecting technologies and methods and the technologies of controlling the trajectories of the complex horizontal wells were established for the well completes in various types of reservoirs. High accurate geosteering technology provided an effective method for developing thin layer with a horizontal

well and then extended to extract oil not only in thick layer but also in thin layer as well as the remaining oil in the top layer of thick positive rhythm reservoir. The screening criteria of the reservoir thickness were reduced from more than 6 m to 1 m. In this period, 336 horizontal wells and 419 lateral wells were put into production, respectively. The initial oil rate of the individual well averaged at 16.9t/d and 12.3t/d, respectively. 1.2 1.2.1

Present situation of special structure well Geology and reservoir engineering Design

The technology series was established for special structural wells, including adaptable criteria for screening and evaluation, fine 3D geological model, quantitative study on the distribution of remaining oil in the mature field, the trajectory design and optimization, productivity prediction, and production controlling. 1.2.2

Drilling technology

The drilling engineering programming for special structure wells was optimized and the software platform was set up. The complex trajectory of special structure wells can be controlled. Integrated geosteering drilling technologies and facilities were developed, as well as casing sidetrack drilling technology. 1.2.3

Completion and production technology

Completion pattern optimization and implementation technology for special structure wells was formed for various types of reservoirs, as well as matching technologies, including perforation, sectional isolation, multi-interval production, anchor packer for producing pays alternation, plugging and crossflow prevention in a slim hole, and downhole fishing tool with augmenter in a horizontal well was developed. 1.2.4

Development of matching software

The integrated software was developed, such as “Horizontal Well Geological Design Software”, “Fit-for-purpose Well Trajectory Design Software”, “Lateral Well Produced Fluid Index and Parameters Optimized Software”, “Horizontal Well Database Enquiry System”, “Horizontal Well Screening Evaluation System”, and so on. The tracing analysis system was established. The design, completion, production, and tracing analysis of special structure wells have been computerized. 1.3 Present application situation of development technology Up to Dec. 2006, 586 horizontal and lateral wells (1 injector) were put into production and the accumulative oil production was 8.25 × 106t (Fig. 1a) from 181 units of 48 oilfields, which included various types of reservoirs, such as bottom water reservoir, roof-faulted reservoir, stratigraphic unconformity reservoir, uncompartmentalized buried hill

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 1

Application situation of special structure wells in Shengli Oilfield

reservoir, extra-super heavy oil reservoir, thick positive rhythm reservoir, thin reservoirs, and offshore oilfield. The oil production of horizontal wells was more than million tons per year after 2003 and up to 1.21 × 106t in 2005, which occupied 4% of the total production in Shengli Oilfield. The number of sidetracking in old wells increased year by year. 742 lateral wells were put into production in 284 units of 42 oilfields, which included the complex faulted and uncompartmentalized, low permeability and heavy oil reservoirs. The oil production was 7.9 × 105t per year and the accumulative oil production was 4.09 × 106t (Fig. 1b). Thus, the special structure wells played a very important role in the sustained and stable development in Shengli Oilfield.

2.1.1 Technological difficulties encountered in the application of horizontal wells

2

2.1.2

New advances on special structure well

The popularization of mature technology was extended continually in Shengli Oilfield since 2003. At the same time, the research on the new technique of special structure wells and its extensive application in frontier were strengthened and new advances have been made, so as to make special structure wells available in various types of reservoirs, such as thin reservoir, buried hill reservoir, complex faulted reservoir, extra-super heavy oil reservoir, and offshore oilfield. 2.1

Thin reservoir

Thin reservoirs are exploited poorly, and therefore, have low recovery and great developing potential. Horizontal wells have the peculiar advantages in developing thin reservoirs.

There are two major difficulties encountered in the application of horizontal wells in thin reservoirs: (1) it is difficult to predict the distribution of thin reservoirs. Since most reservoirs are continental deposits in Shengli Oilfield, fluctuation of reservoir top surface and lateral lithologic variation is fairly obvious. (2) it is difficult to control well path. One reason is that accurate target is difficult to achieve since larger or smaller deviation angles will cause the bit to miss the oil layer. Another is that it is difficult to make the well go through the optimum position of the oil layer so as to ensure production efficiency of horizontal wells. Horizontal well technology in thin reservoir

The integrated technologies were adopted to overcome the difficulties mentioned above. 2.1.2.1

Integrated prediction technology of reservoir

Several techniques, including horizontal slice, seismic facies analysis, coherent analysis, 3-D visualization interpretation, logging restricted seismic inversion, and cross-hole seismic techniques, have been used to ensure accurate reservoir description and mutual verification, and to improve the accuracy of reservoir prediction, for which the thickness errors of predicted layer were not more than 1 m. 2.1.2.2 Technologies of drilling optimization design and high precision trajectory controlling To ensure high accuracy requirement of build-up rate

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 2 Schematic of trajectory section of Well Ying31-ping2

because of limited coverage for horizontal well in thin reservoir, it is necessary to optimize the sectional build-up rate and trajectory with “Non-conventional Well Trajectory Design Software”, and to realize high precision trajectory control by geosteering drilling technology as given below. (1) Special tools. The downhole power motor and adjustable stabilizer were developed, which could be used for short measuring distance and steering radius, which laid the foundation for improving the prediction and controlling precision. (2) Measurement while drilling instruments and formation prediction technology. On the basis of the introduction of FEWD natural gamma ray measuring instrument, geosteering measuring instrument with the national intellectual property rights was developed, and the design and manufacture technique of geosteering double parameters LWD instrument and the interpretation software while drilling geosteering measuring parameters for horizontal wells was established. The interpretation results were considerably more fine and accurate than wireline logging. (3) Trajectory adjustment technique. The 3-D visualization system platform of geosteering was established, which could be used for 3-D displaying trajectory, real-time monitoring, and drilling parameters adjustment, such as drilling pressure, deviation angle, azimuth angle, and so on, according to formation variation, and high precision control of horizontal section trajectory could be realized. 2.1.3

Application effects

Drilling design and high precision trajectory control techniques for thin reservoir can make the vertical and plane error of horizontal section less than 0.5 and 2.5 m, respectively. The different formations and the type of fluids in the formation can be recognized effectively with the self-developed geosteering measuring instrument. The technology has been used in 53 wells, 25 of which belong to Shengli Oilfield, and the remaining belonging to other oilfields in China. The walking through rate in reservoir was up to 94.43%, and the thickness of the thinnest layer encountered was only 0.9 m. Field application showed that these technologies made reserves in thin reservoir develop efficiently, which were difficult to be produced in the past[26-28].

Up to December, 2006, 37 horizontal wells were put into production in less than 3 m oil layers of Shengli Oilfield. The initial average oil rate of individual well was about 18 t/d, which was 3–5 times that of the vertical well adjacent, and the accumulative oil production was 45.62 × 104t. The thickness of the thinnest layer was encountered in Ying31-ping2 well, which was only 0.9 m. The individual well production was 12.4 t/d in the beginning, and the accumulative oil production was 2.74 × 104t (Fig. 2). However, it is difficult to develop such reservoir using vertical wells. 2.2 Thick positive rhythm reservoirs at extra-high water cut stage The successful solution to the high precision drilling problem in thin reservoir development with horizontal wells provided mature technology for the development of thick positive rhythm reservoir at extra-high water-cut stage. Since this kind of reservoir is at the stage of extra high water cut, using special structure wells to develop them is of high risk. Therefore, it is quite important to carry out researches on the distribution of remaining oil and to optimize the technical limit of horizontal wells. 2.2.1

Features of remaining oil distribution

The distribution of remaining oil for thick positive rhythm reservoirs at extra-high water cut stage has two features according to the data of cored inspection well. 2.2.1.1 Remaining oil mainly concentrating in the middle of oil layers. During the period of water flooding, water flows first along the lower and the upper part under the influence of gravity and the difference of reservoir properties. With time passing, strong water washing appears in the lower and the upper part of the oil layer and the remaining oil enriches relatively in the middle part of the oil layer (Fig. 3, oil bearing interval in Ng54+5). 2.2.1.2 Distribution of remaining oil influenced by intraformational bed Intraformational beds are common in positive rhythm oil layers, and play an important role in the distribution of remaining oil for the shelter from hydrodynamic force. The intraformational beds hinder the injected water fingering trend in the lower part influenced by gravity. At the same time, because of separation of interbeds, the upper part of the oil layer cannot be influenced by water flooding, and it is difficult to produce oil from the upper parts with weak hydrodynamic force, and thus, the remaining oil is enriched here (Fig. 3, middle part of Ng54+5). 2.2.2 2.2.2.1

Remaining oil description technology Fine stratigraphic correlation

Based on the theory of sequence stratigraphy, under the

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 3

Profile of water washing in cored inspection well

macroscopic control of sedimentary conceptual model, sublayers were divided into time unit, rhythm section, and flow unit using methods of lithology, fossil organism, and geophysics. Furthermore, reasonable check on the results has been done combined with production performance. 2.2.2.2

Fine structure research

Using the technologies of fine seismic interpretation, cross-hole seismic, coherent analysis, and multi-scale margin detection, the low-grade faults and subtle structures were described accurately and carefully. The accurate description could reach the low-grade faults less than 100 m with fault throw less than 10 m. Subtle structure can be interpreted as small as 1̢5 m. As a result, remaining oil abundant area in small scale could be found. 2.2.2.3 Quantitative identification of sedimentary microfacies Based on the data of cored wells, quantitative identification model has been established by introducing series of parameters included reservoir thickness, porosity, permeability, permeability variation coefficient, median size, and sorting coefficient. Then, quantitative interpretation and computer automatic division of reservoir sedimentary microfacies in non-cored wells were realized finally using the parameters of secondary logging interpretation. 2.2.2.4 Fine well logging interpretation of reservoir parameters

Fine well logging interpretation model of reservoir parameters, which could be fit for digital processing of whole well logging in different stages of water cut, was established after log normalization and combination of the conceptual model and actual data. Fine interpretation of 8 points per meter and ten parameters of each point, which consist of porosity, permeability, permeability variation coefficient, primary oil saturation, remaining oil saturation, remaining oil saturation, water cut, shale content, median size, and sorting coefficient, have been computerized automatically. 2.2.2.5 Fine description and prediction of intraformational bed Based on the theory of sedimentary unit, the integrated description of intraformational bed has been carried out with technologies of thick layer subdivision, correlation of rhythmic unit, and interwell prediction of random modeling. Conventional logs — such as spontaneous potential, natural gamma, resistivity, acoustic wave, and so on — have been processed with Walsh function and wavelet analysis method, and the vertical resolution could reach up to 0.25 m̢0.40 m. 2.2.2.6

Fine reservoir numerical simulation

Based on the geologic research mentioned above, the fine geologic model was established. Numerical simulation research was carried out with large parallel processing numerical simulation software. In history matching, mass dynamic data was fully used to realize fine matching for

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 4

Fig. 5

Technical Policy of Horizontal Well in Thick Positive Rhythm Reservoirs with intraformational bed

Technical Policy of Horizontal Well in Thick Positive Rhythm Reservoirs without intraformational bed

reservoir, such as sealing cored inspection well, infill well, renew well, producer liquid profile, injection profile, tracer test, well test, production, injection, pressure test, liquid level test, etc. 2.2.2.7 Integrated and quantitative description of remaining oil Based on the result of numerical simulation of remaining oil saturations of every sublayer, every well and every grid is calculated quantitatively combining several methods of streamline modeling, water flooding curve, saturation-permeability curve, and water line moving speed. Thus, the remaining oil enriched areas are found. 2.2.3 Technical policies of horizontal wells in thick positive rhythm oil layers According to the characteristics of remaining oil enrichment in thick positive rhythm reservoirs, horizontal wells have the advantage in producing remaining oil. As a result, the main corresponding technical policies limit for horizontal has been studied and formed. (1) It was assumed that intraformational bed existed; then the technical limit for horizontal well is: dimensionless area of intraformational bed, which is equal to the area of

intraformational bed divided by the area controlled by horizontal well, which should be more than 6 (Fig. 4a). The thickness of the remaining oil layer should be more than 3m (Fig. 4b); the dimensionless length of hole section, which is equal to the equivalent diameter of the remaining oil layers divided by the length of horizontal section should be about 0.3 (Fig. 4c); and the production pressure difference should be 1.0̢1.5 MPa (Fig. 4d). (2) If no intraformational bed or intraformational bed has high permeability, the thickness of the remaining oil layer should be more than 5 m (Fig. 5a), and the drawdown pressure should be 0.5̢1.0 MPa (Fig. 5b). 2.2.4

Application effects

A 160m long horizontal section of Well Zhong9-Ping9 in Gudao Oilfield was located in the upper part of oil layer above intraformational bed (Fig 6). The production was 3 times that of adjacent vertical wells and the water cut was only about 33.4%, which was 60% lower than the adjacent vertical wells. The cumulative oil production of Well Zhong-Ping9 was 2.1 × 104t by far 2006. From 2003 to 2006, a total of 5 units for horizontal wells in thick oil layer were adjusted in oilfields of Gudao Oilfield, Gudong Oilfield, and Chengdong Oilfield. 47 horizontal

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 6 Section of Well Zhong9-ping9 in Gudao

wells were designed with controlled reserves of 494 × 104 t and 44 of them were put into production. Accumulative oil production amounted to 26.73 × 104 t, and in prediction, the total incremental recoverable reserves reach up to 201 × 104t[29, 30]. 2.3

Complex fault-block reservoir

Complex fault-block reservoir is one of the reservoirs in Shengli Oilfield, in which special structure wells were applied in large scale and better result was obtained. Not only conventional horizontal wells were extensively used[31,32], but also matching technology of sidetrack drilling was developed and applied widespread[33]. 2.3.1 Difficulties encountered in the development of lateral well Lateral wells have fallen into the low valley after the stage of rapid development, the numbers of which decreased sharply from 121 (2001) to 42 (2002) for the main reasons given below. (1) sidetrack was performed in blocks with relative simple structures; the remaining fault blocks have complicated fracture system, especially, the distribution of remaining oil in middle-late period oilfields is very disperse, and thus, remaining oil description technology should be developed. (2) lack of special casing and tubing in technique. The strength of tubing with diameter of 89mm as casing and small tubing with diameter of 48.3 mm both cannot meet the operating requirements, and the penetration depth using the matching bullet gun with diameter 60mm and bullet with diameter 60mm is shallow, thus affecting production performance of lateral well. 2.3.2

Matching technology

Corresponding

matching

technologies

have

been

developed to overcome the difficulties mentioned above. 2.3.2.1 Remaining oil description technology with focus on description and assemblage of lower-order faults The faults can be divided into six orders, of which the sixth, the fifth, and the fourth orders are known by the name of lower-order faults. The lower-order faults are of short extension and small fault throw, and are difficult to identify and describe. These faults have no controlling effect on the hydrocarbon accumulation, but have great effect on the production strategy, especially on the distribution of remaining oil at late development stage. Thus, the important task is to research on the lower-order faults and their control on hydrocarbon in the late development stage of fault block oilfield. The technology is used to analyze the structural pattern of lower-order faults based on the structure physical and tectonic stress field simulation test, and contributes to conduct the identification and description of lower-order faults, supply basic data for the identification of subtle faults with high-resolution 3-D seismic data processing, poststack seismic data processing and 3D seismic data merging, identify and combine lower-order faults by several technologies, such as full 3-D seismic interpretation, coherent analysis, multi-scale margin detection, cross-hole seismic, integrated interpretation of fault and formation, and so forth, and further improve the interpretation accuracy of fault with production performance and structural pattern. The technologies mentioned above can be used to describe the lower-order faults with fault throw between 5m and 10m and extension length less than 100 m. For example, 5 oil bearing fault blocks were found and the number of faults increased, and incremental proved reserves of 12 × 104 t were calculated during re-description of the fault system in Xin25 fault system.

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 7

Types of Lateral Wells in Complex Fault Block

Based on the interpretation of lower-order faults, the distribution of remaining oil in complex fault block is studied. Research shows that the main enrichment areas of remaining oil are zones situated on top of local subtle structure highs, layers transected by fault, cross-hole stagnant zones, and potential zones with imperfect well pattern. Therefore, four types of lateral wells come into existence correspondingly (Fig. 7), that is, side track in local highs(Fig. 7a), side track in layers transected by fault(Fig. 7b), sidetrack in cross-hole stagnant zones(Fig. 7c), and renew sidetrack on old well (Fig. 7d). 2.3.2.2 Completion and production engineering technology In 2003, a new 3¾ in (ĭ95 mm) small casing was developed, replacing ĭ89mm oil tubing as casings for completion, with internal diameter of 82mm and wall of 6.5 mm. This kind of casing was designed to meet the requirement of STH (side tracked hole) exactly, and the inside diameter accorded with the need of 2Ǫ in (ĭ60.3 mm) bore size tube and 76 mm packer and so on. As a result, it causes zonal withdrawal and injection of oil tubes to be realized. Moreover, the kind of casing can be passed through with the measuring instrument of PND (pulsed neutron decay spectrum logging). To correspond to special ĭ95 mm casing, ĭ68 mm bullet gun and ĭ89-H bullet were developed, which

increased perforation size, penetration depth, and returns ratio of perforation greatly, broadened seepage areas, and decreased over 25% loss of borehole circulation velocity, as compared with ĭ60 mm bullet gun and ĭ60 mm beneficiate bullet. Two particular coiled tubing: thick wall long filament button ĭ48.3 mm tubing and ĭ60.3 mm tubing were developed to match the new casing. Compared with traditional coiled tubing, this special coiled tubing wall thickness increased by 2.8 mm, and thus, mechanical property indexes, such as loadings against sliding, hydrostatic sealing pressure, the minimum strength of thread joint, and so on, were improved enormously. Concurrently, compared to isometric hollow rod, the special coiled tubing could overcome several defects such as poor connecting seal of conical button between hollow rods, small inner diameter of connector, heavy throttle loss, and so on, and could fulfill the operation requirements of sand washing, plugging, and fishing of lateral wells. 2.3.3

Application effects

With the improvement of the completion and production engineering techniques, the application of lateral wells was promoted once more. 355 lateral wells were put into production since 2003; average 89 wells were put into production yearly, and by the end of the year 2006, the

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 8

Profile of Zheng6 buried hill reservoir with extra heavy crude oil

accumulative oil production reached 1.11 × 106 t. Among the 355 lateral wells, 250 wells were applied in complex fault block oil reservoir and average 62 wells were put into production yearly, which was 70.4% of the total wells; the accumulative oil production was 8.44 × 105 t, and was 76% of the total accumulative oil production. 2.4

Offshore field

The reasons that resulted in failing application of horizontal well in the development of offshore field are: it is difficult for horizontal well to control multiple oil layer reserves in main blocks of offshore field; and high investment risk and poor economic benefit at low oil price. In the past few years, along with the significant changes as given below of oil price and development situation in offshore, it is possible for horizontal wells to increase oil production and enhance economic benefit. (1) The high oil price contributed profitable economic conditions. (2) Main blocks with few number of oil layers in new area adjacent and main layer predominating are suitable for the application of horizontal well to increase the oil rate and enhance recovery. (3) The design of horizontal wells and drilling and oil production matching techniques also provide technical support for horizontal wells drilling in offshore field. 12 horizontal wells were put into production from 2004 to 2006 in Chengdao Oilfield; the average oil rate of single well was 57.4 t/d, 2.5 times that of the adjacent vertical well[34]. 2.5

Buried hill extra heavy oil reservoir with bottom water

Zheng6 buried hill oil reservoir is a fractured limestone oil reservoir with extra heavy oil and bottom water; it has not been developed effectively because of poor deliverability of vertical well. 2.5.1

Difficulties encountered in development

The productivity of conventional wells is low because of high viscosity of crude oil. The viscosity of degassed crude is above 31Pa·s at 50ć. The average production of conventional vertical wells is less than 5t/d, and less than 0.3 t/d for most vertical wells. As a result, most vertical wells

were off production for a long time. Bottom water is active. The reservoir profile (Fig. 8) shows that the upper part of buried hill is oil zone with thickness of 120̢170m, and the lower part is aquifer. The integrated geology study shows that the volume of bottom water calculated was more than 80 times that of the oil volume. The extensive high angle fractures make vertical communication excellent. Since the production pressure difference is great with vertical wells development, bottom water coning occurs easily along high angle fractures and water cut rises rapidly; for instance, the monthly incensement rate of water cut reaches 7.64% in Well Zheng 7. 2.5.2

Fine reservoir description

For Zheng 6 block, the reservoir heterogeneity is strong in the vertical and lateral direction, and most of the fractures and pores in the range of 2 m away from the surface of buried hill are filled up with mud; the fractures and cavities are common ranging between 2 m and 40 m away from weathering crust, some of which can be found in the range of 40 m and 80 m, but rarely below 80 m. The distribution of fractures is network pattern with main orientation of NE and NS. 2.5.3

Optimization design of horizontal well

Depending on the advantages of horizontal wells, such as large contact area with oil layers, little production pressure difference, and inhabitations of bottom water coning effectively, decision has been made that Zheng6 block will be developed with horizontal wells entirely. (1) Vertical Location of Horizontal Well. Studies showed that the storage ability and conductivity of reservoir became poor remarkably in the range of 2 m away from the top surface of buried hill, whereas water cut rose rapidly and cumulative oil production decreased at the early stage if the distance of horizontal section away from the top surface of buried hill was more than 20 m. Thus, the location of horizontal well is between 2 m and 20 m from the top surface. The horizontal section was designed to be an arch trajectory with a certain radian to improve the control on the

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 9

Horizontal well location in Zheng6 buried hill reservoir

reservoir. (2) Orientation of Horizontal Wells. In prediction, the high cumulative oil production and low water cut will be gained, in the case that the horizontal section is perpendicular to the fracture development orientation. Therefore, the horizontal section should be perpendicular to the fracture development orientation as much as possible to increase the possibility of meeting with fractures and to improve the development effect. (3) Length of Horizontal Section. The cumulative oil production of horizontal wells increases with the increase of the length of the horizontal section, but the trend slows down gradually. The length between 250 m and 350 m is suitable. (4) Reasonable Daily Fluid rate. Relations between the maximum daily fluid rate and the oil column have been obtained according to the actual production performance and numerical simulation. The reasonable daily fluid rate is about one third of the limit daily oil fluid rate conditioned on keeping 40% height of oil column for OWC. Bottom water coning occurs in case of the daily fluid rate of horizontal well being more than the limit daily liquid rate, and water cut rises fast; otherwise, bottom water moves upward and water cut rises slowly. Hence, the daily fluid rate should be adjacent to the reasonable daily fluid rate. The limit daily fluid rate calculated should be 36.6 m3 with oil column of 155 m, and the reasonable daily fluid rate should be 12.2 m3. 2.5.4

Application effects

13 horizontal wells have been decided to drill in Zheng6 block, out of which 9 have been put into production (Fig. 9).

It is obvious that horizontal well penetrated large reservoir thickness; the average apparent thickness of individual well penetrated was 63.8 m, 5.1 times that of the vertical thickness of 12.4 m. The average daily oil rate of horizontal well was 13.6 t at the early stage, 2.7 times that (8.0 t) of the vertical well, and the water cut was 11.2%, 12% lower than that of vertical wells. The test results showed that the drawdown pressure of horizontal well was 0.45 MPa, only 17% of that of vertical well. The cumulative oil production of horizontal well in the block was 11.2 × 104t in 2006, and the average composite water cut was only 31.4%, while that of vertical well put on production at the same time was 70%, which showed that horizontal well has obvious advantages on controlling bottom water and producing. 2.6

Extra-super heavy oil reservoir

Extra-super heavy oil reservoir refers to the reservoir whose viscosity of ground degassed crude is more than 10 × 104mPa·s at 50ć. In Shangli Oilfield, abundant extra-super heavy oil was trapped in middle-deep depth, which failed to be produced owing to extremely low productivity with conventional huff and puff. Carbon dioxide assisted huff and puff pilot project with horizontal wells was carried out in Blocks f Zheng411 and Zheng32 in 2006. 2.6.1

Difficulties encountered in development

High Viscosity oil and Deep reservoir. In the blocks of Zheng411 and Zheng32, the depth of reservoir is 1340 m; the viscosity of ground degassed oil ranges from 3 × 105 to 3.6 × 105mPa·s at 50ć and more than 1.2 × 105mPa·s at reservoir

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

temperature of 68ć. The oil is difficult to flow in formation conditions and is difficult to be lifted owing to great thermal loss of well bore at such great depth. Difficult Steam Injection and poor testing result in Vertical Well. For Well Zheng 411-1, the steam injection rate was only 7 t/h with injection pressure of 20MPa, and the oil rate was 0.2 t/d; the cumulative oil production was only 3.2 t and the cumulative steam injection was 1463 t. Therefore, it cannot be produced with vertical wells. Reservoir has edge and bottom water. The normal production will be seriously influenced by the active edge and bottom water if controlled improperly.

Extended reach horizontal wells are mainly applied in shoal water oilfields and the reservoirs not suitable for drilling wells on the ground[35]. Extended reach horizontal well has been researched and developed initiatively since 2003, and integrated technologies from design, drilling, completion to production have been established basically. Kendong405-ping1 well has been newly drilled, the vertical depth of which is 1186.4 m; the horizontal deviation is 2073.5 m; the length of horizontal section is 1030 m; and the ratio of horizontal deviation to vertical depth is 1.75. Perforation was performed on the 150m section in the tail on Oct. 2004, and the initial oil rate was 58 t/d.

2.6.2

2.8.2

CO2 assisted huff and puff with horizontal well

Huff and puff with horizontal well may heat oil effectively owing to the large contact area with oil layers, so as to improve oil production. CO2 solution can reduce oil viscosity and be helpful to overcome capillary resistance and friction and promote flow capability of crude oil. Hence, combing the characteristics of horizontal wells and CO2, the development manner of CO2 assisted huff and puff with horizontal well will be beneficial to increase oil production of extra-super heavy oil. 2.6.3

Application effects

12 horizontal wells were designed in blocks of Zheng411 and Zheng32 in 2006, out of which 9 have been put into production. The average initial oil rate is 12t/d with CO2 assisted huff and puff. Well Zheng411-ping1 was put into production early. Compared with the index of the first cycle for well Zheng412 (CO2 assisted viscosity reducing), the injection pressure of horizontal well was 15 MPa, 4 MPa lower than that of vertical well, and the steam injection rate and steam injection of horizontal well were 1.5 times that of vertical well; the circle cumulative oil production, the average oil rate, and the oil/steam ratio were 2240 t, 19 t/d, and 1.02, respectively, corresponding to 12.4, 4.3, and 8.9 times that of vertical well. 2.7

Water injection by horizontal well

One of the horizontal wells, Well Lin2-ping 40, in N33 thin oil layer of Lin2 block with middle-high permeability and bottom water, was converted to injector in 2004, which was used to carry out the water injection test with horizontal well. Compared with adjacent vertical well, the injectivity of Well Lin2-ping40 was 205 m3/d, twice that of vertical well at the same injection pressure; 4 corresponding producers have rapid build-up of fluid and have solved the problem of energy deficiency. 3 horizontal wells have been converted to injectors at present, and experience has been gained in water flooding with horizontal well. 2.8 2.8.1

Exploratory on special horizontal wells Extended reach horizontal wells

Branch wells

Branch wells refer to drilling branch holes of two and above on the original hole to penetrate the same or different oil and gas layers, and to realize production with every branch hole alone or joint. Multiple branch wells are suitable for various types of reservoirs. 2.8.2.1

Branch horizontal wells

A series of drill technologies of branch wells have been established basically in Shengli Oilfield, including directional lateral drilling, reclaiming technology of overlapping string milling, re-entry of branch hole, and so on, and matching apparatus have been developed independently correspondingly. Zhuang1-zhiping1 Well has been drilled in Zhuang1 block, a thick reservoir with bottom water and at high water cut stage (Figs. 10a, 10b). A1B1 and A2B2 were the two branches of Zhuang1-zhiping1 well, which were whole well cemented, and sand control completion was used after perforating (Fig. 10b). Selective string has been designed for production technology to realize commingled or selective production coupled with packer and hydraulic directional valve, and completion technology and matching apparatus of branch wells have been built up progressively. Compared with adjacent horizontal wells after being put into production, the initial oil rate of Zhuang1-zhiping1 well was 10t/d; the initial water cut is 9% lower. Water cut increased slowly during production, and the daily oil rate was 2.5 times as that of horizontal well with single branch at the same liquid rate. 2.8.2.2 Fishbone branched horizontal wells with open hole completion Technology of fishbone branched horizontal well with open hole completion was researched initiatively in 2006. The original hole of fishbone branched horizontal well was open hole screen completion, while the branch hole was open hole completion, which is helpful for drainage area enlargement. A fishbone horizontal well has been drilled in Chengbei26 block of shoal water oilfield at present. In the upper member of Guantao Formation, Chengbei 26 block, Ng(1+2)1 sand body distributes widely with gentle structure; the stratigraphic dip is between 1° and 2°, and the

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

Fig. 10 Schematic of Position and Completion of Well Zhuang1-Zhiping1

reservoir thickness ranges from 8 to 12 m, without edge water and bottom water. The plan of 4-branch horizontal well was designed. The length of the horizontal section for the main hole was 398 m. The target and original hole were fixed at the middle-lower part of the oil layer, about 6m away from the top of the oil layer. The lengths of the 4 horizontal sections were 149 m, 154 m, 149 m, and 120 m, respectively; all branches were at an angle of 20° with the original hole. The drilling of Chengbei 26B-ping 1 well, which is a fishbone branched horizontal well with open hole, was completed in Oct. 2006. The cumulative length of the horizontal sections was 919 m, among which the lengths of the original hole, 1st, 2nd, 3rd, and 4th branch were 403 m, 151 m, 136 m, 145 m, and 84 m,

respectively, and the maximum included angle with original hole was 13.55°, 17.35°, 27.54, and 23.85°, respectively. After finishing drilling, the calculated oil-bearing area controlled by water flood was 0.48 km2, and the original oil in place (OOIP) was 60 × 104 t. Preproduction was conducted with 5mm choke at 5.9 MPa oil pressure on November 3, 2006. The fluid rate was 104.2 t/d, the water cut was 9.0%, and the higher oil rate was 94.8 t/d. The matching technology for such kind of horizontal well was formed at the same time. Since 2003, the number of horizontal wells applied were about 75 yearly, and the number of lateral wells applied increased from 42 (2002) to 117 (2005) year by year. The application of special structure wells has entered a new stage.

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

3

Development trends of special structure wells

The application of special structure wells in Shengli Oilfield is facing the problem of inadequate high-grade reserves at the moment. Most of the incremental reserves were low-permeability, water sensitive, and extra-super heavy oil reservoirs in the past few years. Some major problems, including imperfect production technology of special structure wells, gravel pack sand prevention of long horizontal section in unconsolidated sandstone reservoirs, unmatching sectional fracturing technique in low-permeability reservoirs, and unbalanced development of special structure wells production technology, such as rapid development of horizontal well and lateral well but slow development of extended reach well and branch horizontal well, and fast progress made in middle-high permeability reservoirs but slow progress in low-permeability reservoirs, and so on, cause some troubles to the application of special structure wells. The technical innovation capabilities of special structure wells need to be strengthened, the matching technology of which should be improved. Furthermore, the application fields of special structure wells should be widened through continuously extending technical storage. 3.1 Establishing application technique of special structure wells in complex margin reservoirs 3.1.1 Low permeability reservoir Proven reserves in complex margin reservoirs, such as low permeability thin bedded alternation glutenite, beach-bar sand body, increased year by year, but it is difficult to be produced because of its poor reservoir conditions and low natural energy. The matching technology of horizontal well and special structure wells should be established to ensure effective development of complex margin reservoirs, which possesses a unique advantage in increasing production and efficiency. 3.1.2

Extra-super heavy oil reservoir

The technology of Steam Assisted Gravity Drainage (SAGD) with the combination of straight well and horizontal well or between horizontal wells should be developed, so as to produce the extra-super heavy oil having viscosity more than 10 × 104 mPa·s. 3.2 Improving matching technology for special structure wells 3.2.1 Technology and economic limit of special structure wells in middle- and high-permeability reservoirs Economic, technical, and policy limits of special structure wells under new economic conditions in middle- and high-permeability reservoirs should be studied. The screening, evaluation, description, and optimization of blocks in which special structure wells are applied should be carried out, and the application of special structure wells in these kinds of

reservoirs should be extended. 3.2.2 Horizontal wells with short-radius or short horizontal section used in mature exploitation areas at extra-high water cut stage Under the circumstances of comparatively high oil price at present, horizontal wells with short-radius and short horizontal section should be applied in middle and high-permeability reservoirs, which are at extra-high water cut and the remaining oil widely dispersed, to enhance recovery and production efficiency. 3.2.3 Completion of horizontal wells and reservoir stimulation technology Long horizontal section, gravel-packed sand control completion of horizontal well should be carried out in unconsolidated formation. For low-permeability reservoirs, it is necessary to research the oil layer fracturing technique by horizontal wells, including carrying out studies on fracturing strings and kits, optimizing the fracturing construction and parameters, developing carrying fluid, and propping agent for fracturing of horizontal wells. 3.3 Forming matching technology for special structure wells 3.3.1 Improving advanced branched well completion technology It is necessary to develop advanced completion technology for branched well, including optimizing and improving the construction works and tools, such as whipstock, packer, cementation, joint, and hanger, particularly strengthening the researches on the mechanical tie back between branch hole and original hole, hydraulic seal and selective reentry. 3.3.2

Researching of radial branched well technology

Radial branched well has several additional holes, of which original hole is drilled in the major reservoir and several branch holes penetrate mudstone interbeds interlaminated upward so as to pass multi-oil layers as much as possible. In other words, the well should be designed like a string of sugarcoated haws on a stick to extend the apparent thickness and increase the drainage volume. 3.3.3 Forming matching technology for extended reach horizontal wells It is necessary to develop drilling, completion, and product matching technology for extended reach horizontal wells, with protary steering drilling technology as predominated.

4

Conclusions

Based on the widespread use of special structure wells, Shengli Oilfield accelerates the development of special structure wells and has made some new progress considering the significantly more complicated reservoir types and higher

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

requirements of technique and economy. The researches on reservoir description, distribution of remaining oil, optimization of special structure wells in various types of reservoirs, including thin layer oilfield, thick positive rhythm reservoir at extra-high water cut stage, complex fault-block reservoir, offshore field, bottom water heavy oil reservoir of buried hill, and extra-super heavy oil reservoir, accelerate the application of special structure wells in all the above types of reservoirs. The practice shows that researches and application of special structure wells should be based on the reservoir description and the distribution of remaining oil in mature exploitation areas, and the optimization of reservoir engineering is the key problem. Shengli Oilfield has developed some drilling and completion technology of special structure wells, such as geosteering, old-well sidetracks drilling, extended reach well, branched well, and so on, possesses the relevant independent intellectual property, and has gained good application results. Owing to the difficulty encountered in the application of special structure wells in Shengli Oilfield, it is necessary to stress the research of application technology of special structure wells in complex margin oilfield and matching technology.

[7]

ZENG Fan-hui, GUO Jian-chun, XU Yan-bo, et al. Factors affecting production capacity of fractured horizontal wells. Petroleum

[8]

and

Development,

2007,

34(4):

HUANG Shi-jun, CHENG Lin-song, LI Xiu-sheng, et al. Pressure system analysis model for multi-lateral horizontal well. Acta Petrolei Sinica, 2003, 24(6): 81-86.

[9] LING Zong-fa, HU Yong-le, LI Bao-zhu, et al. Optimization of horizontal

injection

and

production

pattern.

Petroleum

Exploration and Development, 2007, 34(1): 65-72. [10] LIU Yue-tian, ZHANG Ji-chang. Stable permeating flow and productivity analysis for anisotropic reservoir in horizontal well networds. Petroleum Exploration and Development, 2004, 31(1): 94-96. [11] YU Qi-tai, XIE Xu-quan, LUO Hong, et al. A formula for evaluating practicability of producing remaining oil at the top of positive rhythm reservoir by horizontal sidetracking. Petroleum Exploration and Development, 2001, 28(3): 60-62. [12] LI Ke-xiang, ZHOU Yu-hui, SU Yi-nao, et al. Foreign Extended Reach Drilling Technology. Beijing: Petroleum Industry Press. 1998. [13] WANG Rui-he, ZHANG Yu-zhe, BU Yu-huan, et al. A segmentally numerical calculation method for estimating the productivity

Acknowledgements

Exploration

474-477,482.

of

perforated

horizontal

wells.

Petroleum

Exploration and Development, 2006, 33(5): 630-633.

Thanks to the supervision of Liu Xiantai, Li Zhenquan, Yang Yaozhong, the assistance of Niu Xiangyu and Guo Yingchun from Fault Block & Low Permeability Oilfield Research Development, Li Jian, Du Yushan from Offshore Oilfield Research Department in Geological Scientific Research Institute (GSRI), and the vigorous help of Song Shujun from Xianhe Oil Production Factory.

[14] ZHOU Shou-wei, ZANG Jun, JIANG Wei, et al. Extended Reach Drilling Technology and Its Application in Bohai Gulf. Beijing: Petroleum Industry Press. 2002. [15] WANG Jian-yong, HUANG Wen-fen, LI Hui. Forecasting the productivity of horizontal well in Yan 2 block. Oil & Gas Recovery Technology, 2002, 9(3): 80-82. [16] JIANG Shi-quan, JIANG Wei, FU Jian-hong, et al. Research on extended reach drilling technology and its application in Bohai

References

Oilfield. Acta Petrolei Sinica. 2003, 24(2): 84-88, 93. [17] XIONG You-ming, GUO Shi-sheng, LIU Jing-dong. Study on

[1]

WAN Ren-pu, XIE Zhao-yang, ZHENG Jun-de, et al. Horizontal well production technology. Beijing: Petroleum Industry Press. 1995.

[2]

ZHANG

[4]

[5]

Sea. Oil & Gas Recovery Technology, 2003, 10(2): 73-76. [18] QIN Zong-chao, LIU Ying-gui, XING Wei-qi, et al. Application

Chao-chen,

CAI

Jian-hua.

Well

of geo-steering technique of horizontal well in complex fluvial

Exploitation of Heavy Oil Reservoir. Beijing: Information

reservoir—A case from Caofeidian 11-1 Oilfield. Petroleum

Horizontal

Exploration and Development, 2006, 33(3): 378-382.

Research Institute of CNPC 1991.

[3]

A3 well completion method in Pinghu Oilfield of East China

LI Bao-zhu, SONG Wen-jie, JI Shu-hong, et al. Pressure

[19] JIANG Hong-fu, SUI Jun, PANG Yan-ming, et al. Technique of

distribution behavior of horizontal section in horizontal well.

exceptionally low abundance oil reservoir development by

Acta Petrolei Sinica, 2003, 24(2):97-100.

horizontal wells and its application. Petroleum Exploration and

CHEN De-chun, HAI Hui-rong, ZHANG Zhong-ping, et al.

Development, 2006, 33(3): 364-368.

Research on inflow performance relationship of oil – gas –water

[20] ZHOU Hai-min, CHANG Xue-jun, HAO Jian-ming, et al.

three phases for horizontal wells. Petroleum Geology and

Horizontal well development technique and its practice for

Recovery Efficiency, 2006, 13(3): 50-52.

complex fault-block reservoirs in Jidong Oilfield. Petroleum

QU Zhan-qing, ZHANG Qi, WU Zhi-min, et al. Experimental

Exploration and Development, 2006, 33(5): 622-629.

research on electric analogy of the productivity of fractured

[21] LIU Shang-qi, WANG Xiao-chun, GAO Yong-rong, et al.

horizontal well. Petroleum Geology and Recovery Efficiency,

SAGD process with the combination of vertical and horizontal

2006, 13(3): 53-55.

wells in super-heavy oil reservoir. Petroleum Exploration and

[6] WANG Xiao-dong, YU Guo-dong, LI Zhi-ping. Productivity of horizontal

wells

with

complex

branches.

Expoloration and Development, 2006, 33(6) 729-733.

Petroleum

Development, 2007, 34(2): 234-238. [22] XIANG Jian-min. Development technique for horizontal wells in Tarim Oilfield. Petroleum Exploration and Development,

ZHOU Ying-jie / Petroleum Exploration and Development, 2008, 35(3): 318–329

2006, 33(6): 722-728. [23] WANG Jia-hong, LUO Zhi-bin, ZHAO Ming, et al. Analysis on application examples of horizontal wells in China. Beijing: Petroleum Industry Press. 2003. [24] WAN Ren-pu, LIU Xiang-e, WU Qi, et al. Production technology of horizontal wells in different types of reservoirs. Beijing: Petroleum Industry Press. 1997.

layers-taking Ng53 layer in Zhong1 area of Gudao Oilfield. Oil & Gas Recovery Technology, 2004, 11(6): 34-38. [30] YAN Ping, WANG You-qi, YANG Ren-jin, et al. Optimizing design of overall development plan for horizontal wells of Yong12 block in Yonganzhen Oilfield. Oil & Gas Recovery Technology, 2002, 9(5): 44-46. [31] LI Shun-ming, SUN Guo, LIU Zhi-hong. Applying cluster

[25] LIU Xian-tai. Development techniques of horizontal wells in

horizontal wells to the development of complicated fault-block

Shengli Oilfield. Oil & Gas Recovery Technology, 2002, 9(4):

reservoirs. Petroleum Exploration and Development, 2002,

45-47.

29(6): 81-83.

[26] XU Xin-li, YANG Ping, YOU Xing-you. Developing turbidite

[32] YANG Yao-zhong, SUN Huan-quan, WANG Rui-ping, et al.

oil reservoir in high water cut period by horizontal wells-taking

Optimal technology for side-drilling horizontal well in fastigium

Liangjialou Oilfield as example. Oil & Gas Recovery Technology, 2002, 9(4): 45-47. [27] HAN Qing-hua, XUE Ju-feng, ZHANG Xia. Combination of horizontal and vertical wells to develop oil reservoir with low to medium permeability of Ying 93 fault block. Oil & Gas Recovery Technology, 2003, 10(3): 55-56. [28] WANG Qing-gui, PENG Shang-qian. Application of horizontal

faulted reservoir. Acta Petrolei Sinica, 2003, 24(4): 54-57. [33] HAN Zi-xiu. Lateral drilling technology and its application on EOR in Xianhezhuang area. Oil & Gas Recovery Technology, 2001, 8(5): 52-55. [34] ZHOU Ying-jie. Measures to improve water drive recovery efficiency

of

offshore

Chengdao

Oilfield.

Petroleum

Exploration and Development, 2007, 34(4): 465-469.

well technology in Es_1 thin oil bearing formations of Ying31

[35] WANG Shi-yan, WANG Jun. Present situation and developing

fault block. Oil & Gas Recovery Technology, 2003,10(2): 52-53.

prospect for the production technique of long displacement

[29] SHU Qing-lin. Distribution mode of remaining oil and tapping

horizontal wells. Oil & Gas Recovery Technology, 2001, 8(5):

the potential by horizontal wells in thick positive-rhythm oil .

49-51