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Abstract Xinzhao oilfield, a naturally fractured low-permeability field in Daqing, was put into development in 2000 using an inverted nine-spot waterflood pattern with 300m×300m well spacing. Although waterflooding at Xinzhao oilfield had been an economic success, performance had generally been considered disappointing because oil response following expansion and waterflood adjustment was always less than predicted, so an integrated study aiming to improving the development effect of Xinzhao oilfield was conducted. This paper presents the results of a study addressing the impact of fractures on the recovery and on the reservoir management in pattern waterfloods. Geological study and reservoir performance study indicate that several factors result in this seemingly unfavorable performance, one of main reasons are that the inverted nine-spot pattern is not compatible with the orientation of fractures. The production wells on the row of injectors are seriously watered-out and watercut increases very fast. Reservoir simulation studies indicate that oil cut can be improved if the injection pattern is modified from current inverted nine-spot well pattern to direct line drive pattern to take advantage of orientation of fractures. A field test project based on these studies has yielded results that indicate improved economic performance and better development effect. Introduction Waterflooding is the oldest and by far the most important method used by the petroleum industry to increase recovery from both onshore and offshore reservoirs(Singh et al., 1982). Waterflood design is a complex problem that must ultimately be handled on an individual reservoir basis. The waterflood development requires a substantial investment in wells and facilities and optimizing the number and location of well will be key to the success of waterflood project(Jones et al., 1997). Determing the optimum pattern is one of the major challenges associated with the design and implementation of a waterflood or any other drive processes(Christman, 1994). Fractured low-permeability reservoirs contain a large volume of the worldwide oil resource (Saidi, 1983), yet production from these reservoirs has been modest. Taking Daqing oilfield as an example, the total non-producing reserves in Daqing oilfield is 5.36×108 ton, 3.30×108 ton of which is in low permeability reservoirs, accounting for 82.9% of total non-producing reserves(Xia et al., 1996). These data clearly indicate that most of non-producing reserves in Daqing oilfield is in low permeable reservoirs. So the development of low permeability reservoirs is very important for the sustainable development of Daqing oilfield(Li, 1998). One of the challenges in the development of low-permeability field is that waterfloods commonly suffer from low injectivity, poor sweep, and injector-to-producer linkage. These factors tend to degrade waterflood's effectiveness and have facilitated an attempt to use enhanced recovery techniques (Hoffman et al., 2004). An important risk associated with waterflooding under fracturing conditions is that fractures lead to watering-out of wells and fast increase of watercut, with the result that injection water is cycled around rather than being used for sweeping the crude oil. The selection of a flooding pattern is important for the development effect of waterflooding. The proposed optimal waterflood pattern should(Craig et al., 1971): 1)provide desired oil production rate; 2)provide a sufficient water injection rate to support this oil production rate; 3)maximize oil recovery with minimum of water production to lift, handle and dispose of; 4)take advantage of known reservoir rock characteristics such as directional permeability, fractures, dip, etc.; 5)utilize existing wells and thus minimize drilling of new wells; 6)be compatible with the flooding patterns of operators on other leases.
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Lifecycle > Disposal/Injection (0.56)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.98)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.98)
Reservoir Simulation Study on Improvement of Waterflooding Effect for a Naturally Fractured Low Permeability Field in Daqing, China: a Successful Case
Pu, Hui (U. of Wyoming) | Wang, Guofeng (No. 9 Oil Production Co., PetroChina Daqing Oilfield Co. Ltd.) | Li, Yingxin (Research Institute of Production Engineering, PetroChina Daqing Oilfield Co. Ltd.)
Abstract Xinzhao field, developed in 2000, is one of the major naturally fractured reservoirs of Daqing oilfield, China. Production is obtained from the Putaohua(P) sandstone formation at an average depth of 1,338m. After several years' waterflood development, the development effect was deteriorating, many wells were becoming to be stripper wells, and watercut increased greatly, even some wells were seriously watered out. In order to improve the development effect of Xinzhao oilfield, a reservoir study was made in sufficient depth to understand past performance and to develop a long-range development plan, and the proposed pattern modification was performed in Xinzhao oilfield. The purpose of the study is to develop an optimization strategy for waterflood performance. The first step in the process is to better understand the reservoir. One of tools used are Sourceless Microseismic Fracture Monitoring Technology. The Sourceless Microseismic Fracture Monitoring tool is used to determine the characteristics of fractures. The results of Sourceless Microseismic Fracture Monitoring Technology show that the orientation of most of fractures is east-west. The second step is to analyze the past waterflood production performance to know the development characteristics of existing pattern(inverted nine-spot well pattern). The production rate decline is analyzed, and the reasons causing the current poor development effect are identified. The third step is to develop optimization and surveillance recovery strategies. Reservoir simulation approaches are utilized to optimize the well pattern. The recommended plan is pattern modification with strategy of implementing conversions step by step. A field test of waterflood pattern realignment was carried out. This paper presents the results of pattern modification, and the following tracking and modifications strategies. This field test in Xinzhao field is successful and also is an excellent opportunity to demonstrate the method to improve the development effect of naturally fractured reservoir. Introduction Low-permeability fractured reservoirs contain a large volume of the worldwide oil resource (Saidi, 1983), yet production from these reservoirs has been modest. Waterfloods commonly suffer from low injectivity, poor sweep, and injector-to-producer linkage. These factors tend to degrade waterflood's effectiveness and have facilitated an attempt to use enhanced recovery techniques (Hoffman et al., 2004). It is well known that the geological condition of low permeability oilfield is very complex, and it is difficult to develop low permeability reservoir. Therefore, companies face more challenges when developing low permeability field due to its low productivity. However, the reserves in low permeability reservoirs is accounting for a higher percentage of all reserves. Taking Daqing oilfield as an example, the total non-producing reserves in Daqing oilfield is 5.36×108 ton, 3.30×108 ton of which is in low permeability reservoirs, accounting for 82.9% of total non-producing reserves(Xia et al., 1996). This data clearly indicate that most of non-producing reserves in Daqing oilfield is in low permeable reservoirs. So the development of low permeability reservoirs is very important for the sustainable development of Daqing oilfield.
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
Abstract Based on the non-Darcy flow characteristics of surfactant flooding, considering the changes of threshold pressure and influence of surfactant on convection, diffusion, adsorption and retention, a surfactant flooding mathematical model of three-dimensional, two-phase, three-component was established. A new method for the treatement of relative permeability curve and theoretical calculation equation for adsorption quantity of surfactant were derived, which enhances the matching degree between mathematical model and field practice. The method of implicit pressure, explicit saturation, and implicit concentration was used to solve equations and a simulator was developed. This simulator was used to perform the numerical simulation study for the pilot test of surfactant flooding in Chao 522 Block of Daqing oilfield, the optimal injection scheme was selected. After the optimized plan was carried out in oilfield, the desirable effects, like pressure-reducing, injection rate increase, and oil recovery increase, were achieved. The average oil increase for single well reaches 30%, the ratio of cost to revenue is above 1:3, so the very good development effect and economic effect were obtained. Introduction The indoor experiments show that the surfactant flooding can lower the threshold pressure and increase the oil recovery efficiency of low permeability oilfield(Liu et al. 1987). Several pilot tests of surfactant flooding were carried out in Daqing's low permeability oilfields, such as Yushulin oilfield and Chaoyanggou oilfield, the objectives of pilot tests are to reduce the injection pressure, to increase the injection rate and to enhance the oil recovery. The experimental screening of surfactant was finished, but the theoretical study on surfactant flooding in low permeability oilfield is few, and the reservoir simulation software that include the threshold pressure is not reported(Sun et al., 1996). Because the cost of surfactant is comparatively high, the amount of surfactant used should be first determined for the field application to obtain the maximum economic benefit, so it is very important to conduct reservoir numerical simulation study. On the basis of compositional model, a mathematical model of surfactant flooding was established, in which the changes of threshold pressure and relative permeability which are caused by surfactant flooding, and influence of adsorption and retention of surfactant in the reservoir are included in the model. This model was used to optimize the injection plan for pilot test of surfactant flooding in Chaoyanggou oilfield of Daqing, in order to provide a theoretical basis of decision for the development of oilfield. Experiment of Surfactant Flooding on Low Permeability Cores Experimental Results In order to study the non-Darcy flow characteristics of surfactant flooding in low permeability reservoir, the surfactant flooding experiment on reservoir cores was conducted. The displacing liquid is solution of nonionic alkanol acid amide surfactant and auxiliary agent, which can reduce the interfacial tension between crude oil and water of Chaoyanggou oilfield to reach ultra low interfacial tension(IFT). The experimental results are shown in Table 1. As we can see from Table 1, after injecting the displacing liquid of surfactant, the pressure of succeeding waterflood reduced by 40% compared with value of pre-injection of surfactant solution, so the displacing pressure was significantly reduced, compared with waterflood, the recovery efficiency is enhanced by 5%. In order to further determine the effect of surfactant concentration on the threshold pressure gradient, the relationship between surfactant concentration, water saturation and threshold pressure gradient were measured(Fig. 1). As is shown in Fig. 1, with the increase of surfactant concentration and water saturation, the threshold pressure gradient reduces gradually, but the decrease extent becomes smaller.
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
Abstract Development and production of coalbed methane involves the production of large volumes of water. The salinities and sodium adsorption ratios of coalbed methane (CBM) water from the Powder River Basin range from 370 to 1,940 ppm and 5.6 to 69 respectively. Surface discharge of CBM water can create serious environmental problems; subsurface injection is generally viewed as economically nonviable. It has been shown that oil recovery from reservoir sandstones can be improved by low salinity waterflooding for salinities ranging up to 5,000 ppm. There may be both technical and regulatory advantages to application of CBM water to oil recovery by waterflooding. Thin section and scanning electron microscope studies of the mineral constituents and distribution of Tensleep and Minnelusa sandstones show they are typically composed of quartz, feldspar, dolomite and anhydrite cements but have very low clay content. The sands contain interstitial dolomite crystals in the size range of up to about 10 microns. Three sandstone cores from the Tensleep formation in Wyoming were tested for tertiary response to injection of CBM water. The cores were first flooded with high salinity Minnelusa formation brine of 38,651 ppm to establish residual oil saturation. Synthetic CBM water of 1,316 ppm was then injected. Tertiary recovery by injection of CBM water ranged from 3 to 9.5% with recoveries for all but one flood being in the range of 5.9 to 9.5%. Previous studies showed that the presence of clay was needed for response to low salinity flooding. As a test of the recovery mechanism, a Tensleep core was preflushed with 15% hydrochloric acid to dissolve the dolomite crystals. The treated core showed no tertiary recovery or pressure response to CBM water. Introduction Coalbed methane (CBM) is a significant source of energy and now accounts for 7.5% of gas production in the conterminous United States. In Wyoming, CBM production contributes 18% of the total gas production (WOGCC, 2006). The Powder River Basin (PRB) in Wyoming and Montana is one of the most active areas of development. It is estimated to contain 61 trillion cubic feet (Tcf) of natural gas in-place, with 39 Tcf being technically recoverable (ARI, 2002). There were 19,523 CBM wells in the Wyoming portion of the PRB at the end of 2006 (WOGCC, 2006) (Fig. 1). Planners forecast as many as 81,000 additional CBM wells (Fisher, 2003). Development of CBM production first requires dewatering of the coal seams. CBM water presents a serious disposal problem which complicates CBM development. For the last 3 years, CBM water production in the PRB alone has been about equal to one third of the total water associated with oil and gas production in Wyoming (Table 1). The majority of the water has high sodium adsorption ratios. Total dissolved solids (TDS) of water co-produced with coalbed methane in the Wyoming portion of the Powder River Basin range from 370 to 1,940 mg/L with a mean of 840 mg/L (Rice, 2000). The sodium adsorption ratios (SAR, the ratio of sodium to calcium and magnesium) range from 5.6 to 69 (Pierce, 2004). Most of this water has limited suitability for domestic and animal consumption or for agriculture. Commonly practiced surface disposal has a range of adverse effects. Disposal into rivers has been contested. Other problems involved with the extraction of such large volumes of groundwater include impacts on domestic water wells and natural springs, water rights, lowering of water tables, and groundwater recharge issues. Under the Environmental Protection Agency's Underground Injection Control (UIC) program, subsurface re-injection of CBM water is categorized under the restrictive Class V injection which sometimes makes the disposal uneconomic. To date, only a minimal amount of PRB CBM water has been re-injected (Table 1). Environmentally sound and economically viable disposal of CBM water has become crucial to continuous CBM development in Wyoming.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.88)
- Geology > Mineral > Silicate > Phyllosilicate (0.69)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.67)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.66)
- North America > United States > Wyoming > Powder River Basin > NPR-3 > Teapot Dome Field > Wall Creek Formation (0.99)
- North America > United States > Wyoming > Powder River Basin > NPR-3 > Teapot Dome Field > Tensleep Formation (0.99)
- North America > United States > Wyoming > Powder River Basin > NPR-3 > Teapot Dome Field > Sussex Formation (0.99)
- (12 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Coal seam gas (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
Abstract The naturally fractured reservoirs play an important role in the stable output of Daqing oilfield, which is the largest field in China. But after several year's development, many wells are becoming to be low efficient wells, the production rate is sharply declining and watercut increased greatly. To improve current development effect, research on how to improve the waterflood effect was carried out, and a pilot test was implemented. The geological study and the multidisciplinary investigation were first performed. Sourceless microseismic fracture monitoring technique shows that there are natural fractures. The statistics results of sourceless microseismic testing of 36 wells indicate that the total number of fractures is 94, among them, there are 23 east-west fractures, occupying 24.15%, 11 north-east fractures(11.17%), 33 east-west fractures(35.11%), and 27 north-south fractures(28.17%). Also pressure buildup cure shows that there exist inflexion points, which indicates that there are natural fractures. Based on the above research results, integrating detailed reservoir description with reservoir numerical simulation, the injection-production adjustment plan and infill drilling were designed. A field test was carried out: the high watercut wells and low production wells on injection line are converted to injection to form a line drive pattern. This field test in the Daqing field is an excellent opportunity to:demonstrate the method to improve the development effect of mature naturally fractured reservoir, show that this should be of reference value to improve the development effect of field. Introduction Xinzhao Oilfield is Daqing Oilfield's typical naturally fractured low permeability field, and was put into production in 2000. 96 development wells and 4 control wells were drilled in December of 2000 in Gu 634 Block of Xinzhao oilfield, the production capacity was 8.89×104t. There were 75 producing wells, the average perforated effective thickness was 4.1m, the initially average daily oil production rate per well was 3.5t, the average intensity of oil production was 0.86 t/d·m; Later because of adjustment of production capacity plan, an additional 20 wells were drilled in the external part of Gu 634 Block, the number of production wells was 92, the average perforated effective thickness was 4.7m, the initially average daily oil production rate per well was 3.2t, the average intensity of oil production was 0.68t/d.m. With development of oilfield, a lot of wells were low efficient wells, the injection-production ratio was high, the production rate was gradually lowering, the development benefit was worsening. Through the study and analysis, the reasons for low development effect were attributed to the injection-production system. Therefore, Daqing Oilfield Co. Ltd. wants to apply waterflood pattern realignment to improve the development effect. Based on geological characteristics of Xinzhao oilfield, the reservoir numerical simulation research using reservoir simulator IMEX of CMG was carried out for Gu 634 Block. In this paper, the well pattern realignment, optimum voidage replacement ratio, and timing for conversion were studied and presented, the optimum injection-production system scheme is selected to improve the development status of Xinzhao oilfield. The injection-production system scheme was carried out in field, the development effect is improved and the considerable economic benefit was achieved. Analysis of Fractures As we know fracture orientation has a significant influence on the development effect of pattern waterfloods, so it is very important to know the characteristics of fractures in the reservoir.
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
- North America > United States > Louisiana > China Field (0.97)