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01 October 2023, Volume 44 Issue 5 Previous Issue    Next Issue

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OIL AND GAS EXPLORATION

Natural Gas Enrichment in Carbonate Gas Reservoirs of Taiyuan Formation in Yishaan Slope，Ordos Basin LI Yanrong, LI Jing, SU Wenjie, SHI Lei, SUN Rui, ZHU Yushuang 2023, 44 (5):  509-516.  doi: 10.7657/XJPG20230501 Abstract ( 256 )   HTML ( 26 )   PDF (18631KB) ( 176 )   Save To determine the distribution of the carbonate gas reservoirs in Permian Taiyuan formation in Yishaan slope of the Ordos basin, based on the data of drilling, well testing, logging, and formation testing, the carbonate gas reservoirs in Taiyuan formation were analyzed using field outcrops, core samples, thin sections, electron microscopy scanning, high-pressure mercury intrusion, and fluid inclusion temperature measurements, and then sedimentary microfacies, petrographic characteristics, physical properties, pore structures, and fracture distribution were studied of the reservoir. The results indicate that the carbonate gas reservoirs in Taiyuan formation are low-porosity and low-permeability lithological gas reservoirs. Favorable plays control the reservoir distribution and gas enrichment. The gas reservoirs `are mainly distributed in the bioherm and bioclastic shoal microfacies zones. Bioherms are found in the eastern part of the study area, including Jiaxian, Zizhou, and Qingjian, while bioclastic shoals are developed in the western part of the study area, including Hengshan, Jingbian, and Pingqiao, exhibiting an obvious zoning of facies from west to east. The carbonate rocks in Taiyuan formation consist of micritic bioclastic limestone and algal-bounded limestone, in which biogenic pores, intercrystalline pores, dissolution pores, and microcracks serve as accommondation. Fractures play a crucial role in migration of oil and gas, and their development contributes significantly to the natural gas enrichment in the reservoirs. Figures and Tables | References | Related Articles | Metrics

Architecture of Shallow-Water Delta Reservoir of Huagang Formation in C Oilfield，Xihu Sag HE Xianke, LOU Min, CAI Hua, LI Bingying, LIU Yinghui, HUANG Xin 2023, 44 (5):  517-527.  doi: 10.7657/XJPG20230502 Abstract ( 154 )   HTML ( 12 )   PDF (7528KB) ( 119 )   Save In order to improve the accuracy of reservoir characterization for purpose of tapping the potential of remaining oil in the middle to late oil and gas field development stage, taking the shallow-water delta reservoir of the Huagang formation in C oilfield, Xihu sag, as an example, the reservoir architecture was investigated by using core, grain size, logging, and seismic data. The architecture patterns of composite channel sandbodies of shallow-water delta facies were established, and their spatial evolution was clarified. The results show that the H3c layer represents the upper plain-channel deposit of shallow-water-delta facies, which is dominated by vertically stacked thick sandbodies; the H3b layer represents the lower plain-channel deposit of shallow-water delta facies, in which laterally-migrated medium-thick sandbodies are developed; and the H3a layer represents the shallow-water delta-front deposit, which is featured with isolated thin sandbody. The development of vertical sandbodies was controlled by middle-term base-level cycle. As the lake level rose, the shallow-water delta in the study area formed a retrogradational sequence, and sandbodies evolved from sheet-like to isolated belt-like, resulting in deteriorating reservoir connectivity. Figures and Tables | References | Related Articles | Metrics

Maturity Evaluation of Niutitang Formation Source Rocks in Tongren Area，Northeast Guizhou LIU Kuiyong, WU Tao, LU Shufan, PAN Yingjuan, AN Yayun 2023, 44 (5):  528-534.  doi: 10.7657/XJPG20230503 Abstract ( 141 )   HTML ( 12 )   PDF (590KB) ( 128 )   Save To determine the exploration potential of the shale gas in the Cambrian Niutitang formation in the Tongren area, northeast Guizhou, on the basis of X-ray diffraction experiments, the maturity of the shale of Niutitang formation-Bianmachong formation from Well QTD-1 was tested by using methods of bitumen reflectance, illite crystallinity and laser Raman spectroscopy. The results show that the shale of Niutitang formation-Bianmachong formation lacks vitrinite, making its maturity difficult to be evaluated using conventional vitrinite reflectance. The shale is not evaluated satisfactorily by using the reflectance of bitumen, due to its complex genesis and the impact of bitumen heterogeneity. The illite crystallinity method can only provide a rough range of maturity, with relatively large error due to the presence of clay minerals. In contrast, the laser Raman spectroscopy method is less affected by heterogeneity and has advantages such as simple sample preparation and non-destructive testing, which proves to be a more ideal testing approach. The equivalent vitrinite reflectance of the black shale of Niutitang formation in the study area ranges from 3.41% to 3.50%, indicating a late overmature stage. Figures and Tables | References | Related Articles | Metrics

Characteristics of Fractures and Their Controls on Yanchang Formation Reservoir in Ordos Basin XIAO Zhenglu, LU Jungang, LI Yong, ZHANG Hai, YIN Xiangdong, ZHOU Xiang 2023, 44 (5):  535-542.  doi: 10.7657/XJPG20230504 Abstract ( 127 )   HTML ( 12 )   PDF (1050KB) ( 103 )   Save In order to determine the temporal continuity and spatial orderliness of hydrocarbon charging and accumulation in fault areas, taking the Shangzhenzi farm-Zhuanjiao area at the southern margin of the Ordos basin as an example, the relationship between fracture formation period and reservoir distribution was analyzed, and the controls of fractures on Yanchang formation reservoir was discussed. The study shows that the fractures of three periods (Yanshanian movement episode II and III, and Himalayan movement) are developed in Yanchang formation, showing varying impacts on hydrocarbon migration and accumulation. Near-source oil reservoirs captured all the hydrocarbons generated from the source rocks in immature and mature stages, which were subsequently destroyed during the Yanshanian episode III and the Himalayan movement, leading to oil migration towards the areas far away from source rocks. In the southern part of the study area, close to the Weibei uplift, fractures are well connected longitudinally and sand bodies are well developed, allowing oil enrichment primarily in reservoirs far away from source rocks. In the northern part of the study area, oil is predominantly retained in reservoirs near source rocks. Consequently, fractures and sand bodies are connected to form a transport network that plays a role in adjusting reservoirs. By virtue of multi-stage fractures, resources in reservoirs near or far away from source rocks can be complemented and integrated. Figures and Tables | References | Related Articles | Metrics

Diagenetic Evolution and Its Significance of Zeolites in Sedimentary Rocks ZUO Rusi, ZENG Xiang, CAO Zhongxiang, CAI Jingong, ZHANG Kuihua, ZHANG Guanlong 2023, 44 (5):  543-553.  doi: 10.7657/XJPG20230505 Abstract ( 141 )   HTML ( 13 )   PDF (4982KB) ( 86 )   Save Zeolites are widely distributed in sedimentary rocks, and they are diverse in genesis and complex in evolution characteristics. Controlled by sedimentary environment and diagenetic conditions, zeolites of different genesis are formed in different diagenetic sequences, and exhibit distinct combinations, occurrences, and frameworks. Zeolites can be divided into primary zeolites, hydrothermal zeolites, volcanic-altered zeolites, and mineral-transformed zeolites. Zolite framework can be characterized by the Si/Al ratio, based on which the zeolites are categorized into high-silica and low-silica zeolites. Zeolites play a strong catalytic role in hydrocarbon generation from source rocks. High-silica zeolites have lower catalytic activity, but slower deactivation rate than low-silica zeolites, and exhibit good selectivity. Zeolite cementation and dissolution have constructive and destructive effects on reservoirs, respectively. In different diagenetic sequences, zeolites show varying impacts on reservoir properties. The transformation of clay minerals to zeolites enhances the brittleness and water sensitivity of shale. Brittleness will increase the fracability of shale reservoirs, while water sensitivity will reduce reservoir permeability. Figures and Tables | References | Related Articles | Metrics

Distribution and Potential Tapping Strategies of Remaining Gas in Tight Sandstone Gas Reservoirs SHI Yaodong, WANG Liqiong, ZANG Yicheng, ZHANG Ji, LI Peng, LI Xu 2023, 44 (5):  554-561.  doi: 10.7657/XJPG20230506 Abstract ( 158 )   HTML ( 13 )   PDF (1855KB) ( 118 )   Save The Su 36-11 block in the central area of Sulige gas field has been developed for 17 years, with high degrees of development and reserves producing. The strong reservoir heterogeneity in this block leads to uneven producing of reserves and complex distribution of remaining gas. Distribution determination and potential tapping of the remaining gas are crucial for maintaining stable production in the gas field. By accurately characterizing the reservoir architecture, the main factors influencing remaining gas distribution were identified, the distribution patterns of different types of remaining gas were determined, and corresponding strategies for recovering the remaining gas were proposed. The research results show that the gas-bearing sand bodies in the study area are mainly distributed in the 4th-order architecture units, such as channel bar and point bar, these sand bodies are significantly affected by various levels of flow barriers, with small overall scale, poor connectivity, width of 150-500 m and length of 300-800 m. The main NE-SW sand belt in the block has been developed the most, with low formation pressure, and the remaining gas is mainly distributed in the lower He 8 member in the northwestern part of the block. Remaining gas, whose distribution is mainly influenced by reservoir heterogeneity and uneven development, can be divided into five types: gas uncontrolled by well pattern, gas in composite sand body flow barrier, gas in secondary pay zone unexploited by horizontal well, gas in unperforated gas-bearing layer in vertical well, and gas unproduced. Four potential tapping measures were proposed, including well infilling, reperforation, sidetracking and potential tapping in exsisting wells. According to the adjusted development plan, it is predicted that stable production can be maintained for 7 years with the recovery efficiency reaching 45%. Figures and Tables | References | Related Articles | Metrics

RESERVOIR ENGINEERING

Establishment and Application of Generalized Characteristic Curves of Gas-Water Miscible Flooding JIA Rui, YUAN Quan, TANG Xin, LYU Qiqi, GAO Wenjun 2023, 44 (5):  562-571.  doi: 10.7657/XJPG20230507 Abstract ( 123 )   HTML ( 15 )   PDF (769KB) ( 51 )   Save Considering the limited methods for evaluating reservoir development performance using gas-water miscible flooding characteristic curves, a concept of underground water-gas cut was introduced. By analogy with the generalized mathematical model of water cut variation in water flooding reservoirs, generalized gas-water miscible flooding characteristic curves and the corresponding generalized mathematical models of underground gas-water cut variation were established. The generalized gas-water miscible flooding characteristic curve is a Type A water-alternating-gas (WAG) injection characteristic curve when n=0 and m=0, and a Type B WAG injection characteristic curve when n=1 and m=0. By varying the values of n and m, the generalized gas-water miscible flooding characteristic curve can be transformed into S-shaped, convex, S-convex, S-concave, and concave gas-water miscible flooding characteristic curves. For purpose of field application, a general formula for the generalized gas-water miscible flooding characteristic curve and solution method for the corresponding mathematical model combining underground gas-water cut variation were provided. The application to the evaluation of the development performance of WAG injection in the reservoir of Sanjianfang formation in Pubei oilfield, and of gas cap gas + edge water displacement in S31 reservoir in Jinzhou oilfield shows a high fitting accuracy. This method can be a reference for other reservoirs. Figures and Tables | References | Related Articles | Metrics

Enhanced Oil Recovery by CO2 Huff-n-Puff in Tight Oil Reservoirs in Mazhong Block，Santanghu Basin LI Shirui, ZHAO Kai, XU Jiangwei, Murzhaty ASKUR, XU Jinlu, ZHANG Xing 2023, 44 (5):  572-576.  doi: 10.7657/XJPG20230508 Abstract ( 121 )   HTML ( 7 )   PDF (596KB) ( 71 )   Save The tight oil reservoirs in the MZ block of the Santanghu basin are characterized by medium-high porosity, ultra-low permeability, and high oil saturation. In the initial development stage, high production rate was achieved by virtue of volume fracturing in horizontal wells, but declined greatly. In the late stage, the reserves were effectively produced through water huff-n-puff. After years of development, the effect of water huff-n-puff became worse. The current recovery percent of reserves is only 5.6%. For further enhancing the oil recovery, CO2 huff-n-puff experiments were conducted in five horizontal wells. The results show that CO2 plays a pivotal role in enhancing recovery in tight oil reservoirs through the mechanisms such as swelling, energy augmentation, viscosity reduction, light component extraction, and fluid mobility improvement. The impact of CO2 varies throughout the injection, soaking, and production stages, leading to alteration in crude oil properties. CO2 can enhance oil recovery and also demonstrate a high storage rate, offering both economic and social benefits. CO2 huff-n-puff is adaptable and promising for tight oil reservoir development. Figures and Tables | References | Related Articles | Metrics

Horizontal Well Infilling and Water Flooding Tracking Adjustment for Production Increase in Low Permeability Reservoirs in X Oilfield ZHOU Jiamei 2023, 44 (5):  577-582.  doi: 10.7657/XJPG20230509 Abstract ( 129 )   HTML ( 9 )   PDF (552KB) ( 79 )   Save In X oilfield, the reservoirs exhibit poor physical properties, a small number of layers vertically, and the presence of small faults in complex distribution, which lead to poor effect of vertical well development and ineffecient displacement of the existing well pattern. Based on the successful development of pre-existing horizontal wells and infilled horizontal wells in the pilot test in 2014, a study was conducted on horizontal well infilling and tracking adjustment techniques in the areas with inefficient waterflooding by vertical wells and in the unswept areas near fault zones. Through logging-seismic combination and comprehensive dynamic-static analysis, the areas with stable reservoirs, low water-out risk, and enriched remaining oil were identified for well infilling. By optimizing the orientation and horizontal section length of horizontal wells, the fracturing density and fracture length were optimized to enhance the productivity of horizontal wells. The injection-production process was optimized by implementing the waterflooding tracking adjustment strategy of early-stage intermittent water injection and weak injection via the injector in an adjacent row + strong injection via the injector in a row apart. Following these approaches, a total of 19 infilling horizontal wells were drilled in the X oilfield in 2019, achieving a sandstone-encountered rate of 83.0%. The initial daily oil production per well reached 7.4 t, with a comprehensive water cut of 28.8%. An effective displacement system was established, resulting in an increase in the oilfield’s production rate from 0.8% to 1.5%, and improving the overall development effect of X oilfield. Figures and Tables | References | Related Articles | Metrics

Water Invasion Characteristics and Residual Gas Distribution in Fractured-Porous Carbonate Reservoirs XIE Peng, CHEN Pengyu, ZHAO Hailong, Xu Jianting 2023, 44 (5):  583-591.  doi: 10.7657/XJPG20230510 Abstract ( 131 )   HTML ( 11 )   PDF (1507KB) ( 99 )   Save Water channeling often occurs in gas wells during the production of fractured-porous carbonate gas reservoirs with edge/bottom water. A simulation experiment on water invasion mechanism was performed by using a visualized microscopic model and under the formation conditions simulated by the high-temperature high-pressure online nuclear magnetic resonance detection system, to study the distribution of residual gas. The distribution of intrusive water was characterized by the T2 spectrum obtained from pulse sequence testing. The results show that the pore-throat ratio, coordination number, and fracture width have significant impacts on water invasion and residual gas distribution. In porous reservoirs, invasion water first enters large pores and then small pores. In fractured-porous reservoirs, where the distribution of fractures has an influence on the water invasion mode, intrusive water enters the fractures and then the medium-large pores. In water-invaded porous reservoirs, 37.7% of the residual gas exists in small pores, and 62.3% in large pores. In water-invaded fractured-porous reservoirs, a little residual gas is in fractures, 4.8%-26.8% of the residual gas in small pores (where the residual gas is difficult to recover), and 94.7%-69.2% in medium-large pores. The residual gas saturation index was evaluated with the water invasion proportion in medium-large pores as an objective function, and the main controlling factors include fracture penetration degree, water volume ratio, fracture width and gas production rate. The well trajectory should be optimized in the fracture zones and kept away from the fractures that communicate with edge/bottom water. Furthermore, well production rate should be optimized to delay water breakthrough. After water breakthrough in gas wells, the gas production rate should be appropriately reduced to drive intrusive water into medium-large pores and reduce residual gas in the medium-large pores, thus enhancing the gas recovery. Figures and Tables | References | Related Articles | Metrics

Experimental Study on CO2 Flooding and Storage in Chang 8 Ultra-Low Permeability Reservoir in District Huang 3，Jiyuan Oilfield CHEN Xiaodong, WANG Jin, SONG Peng, LIU Jian, YANG Weiguo, ZHANG Baojuan 2023, 44 (5):  592-597.  doi: 10.7657/XJPG20230511 Abstract ( 125 )   HTML ( 10 )   PDF (630KB) ( 97 )   Save In order to determine CO2 flooding and storage mechanisms in the ultra-low permeability reservoir in Jiyuan oilfield, long core experiments were performed to understand the performance of enhanced oil recovery (EOR) and CO2 storage under different flooding techniques. The results show that the CO2-water alternating injection after water flooding yields the highest recovery factor, followed by CO2-water alternating flooding, while continuous CO2 injection exhibits the lowest recovery factor. CO2 breakthrough is a crucial factor influencing recovery factor, and alternating injection can suppress gas channeling. CO2 is dominantly stored in the large pores of the reservoir, and the CO2-water alternating flooding is more conducive to CO2 storage in the small pores than pure CO2 flooding. Continuous CO2 injection, CO2-water alternating flooding, CO2-water alternating injection after water flooding, and CO2 injection after water flooding exhibit a descending order in CO2 storage efficiency. Figures and Tables | References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

A Data-Driven Method to Reconstruct Reservoir Flow Field FENG Gaocheng, LI Jinman, LIU Yuming, YIN Yanjun, WEI Zhiyong, ZHANG Qiang, MENG Fankun 2023, 44 (5):  598-607.  doi: 10.7657/XJPG20230512 Abstract ( 124 )   HTML ( 9 )   PDF (4395KB) ( 79 )   Save The production stabilization and water-cut control of multilayer clastic reservoirs have always been a hot topic in oilfield development. At the medium-high water-cut development stage, oilfields usually exhibit obvious decline of production, scattered distribution of remaining oil, and prominent development conflicts between layers. For these oilfields, there is an urgent need for appropriate optimization and control methods to achieve sustained and stable production. Based on the Bayesian posterior probability method and reservoir streamline simulator, by applying a random maximum likelihood function, the history matching problem was solved and a space data set was constructed. Furthermore, by using finite-memory quasi-Newton gradient method, the data space set was inverted to predict the future. The transient flow velocity of the reservoir flow field was characterized by integrating Pollock streamline tracing method. Thus, a reservoir flow field reconstruction method based on data space inversion was proposed. This method allows real-time optimization of the reservoir injection-production parameters without the need for complex and repetitive calculations. It overcomes the limitations of traditional optimization methods in finely describing flow field evolution and fills the gap in the application of data space inversion in flow field optimization. Taking reservoir B in the Bohai oilfield as an example, the proposed method was used to reveal the mechanism of the reservoir injection-production structure optimization and intuitively demonstrate the process of reservoir flow field optimization. The field application results show that the overall water cut of the reservoir is relatively steady, the scattered remaining oil in the target flooding unit is effectively exploited, and the swept area of water flooding expands by 24.85%, indicating a remarkable flow field control effect. These digitalization efforts for reservoirs will provide valuable reference for the development and data-driven flow field control of similar medium-high water-cut oilfields. Figures and Tables | References | Related Articles | Metrics

Methods for Calculating Oil Column Height in Reservoirs Controlled by Deep and Large Faults WANG Rujun, WANG Peijun, NIU Ge, WANG Huailong, ZHANG Jie, LIANG Ruihan, ZHAO Xinyue 2023, 44 (5):  608-612.  doi: 10.7657/XJPG20230513 Abstract ( 143 )   HTML ( 7 )   PDF (586KB) ( 135 )   Save The reservoirs controlled by deep and large faults are generally thick and deep. Therefore, a well cannot penetrate completely through an entire reservoir. For calculating the oil column height in fault-controlled reservoirs, a physical model of oil column height in fault-controlled reservoir was established. On this basis, the idea of the wellbore temperature profile extrapolation method was discussed, a formula for calculating oil column height with the conversion method of oil-water column pressure coefficient was derived, and the dynamic reserves inverse method considering the cuboid drainage area and the equivalent flow resistance method considering the influence of gravity were proposed. The four methods were applied to two wells drilled into a fault-controlled reservoir in Fuman oilfield of Tarim basin. The results show that the oil column heights calculated by the four methods are consistent, and the average oil column heights of the two wells are 675.39 m and 634.60 m, respectively. Figures and Tables | References | Related Articles | Metrics

Experimental Study on Nitrogen-Assisted Gravity Drainage in Karst Reservoirs of Different Genesis CHENG Hong 2023, 44 (5):  613-617.  doi: 10.7657/XJPG20230514 Abstract ( 110 )   HTML ( 4 )   PDF (1980KB) ( 46 )   Save The reservoirs in the Tahe Oilfield are complex and the remaining oil in the middle-lower part is difficult to recover. Based on the geological data and modeling results, a reservoir profile model considering reservoir type, fracture distribution and fracture-vug configuration was constructed. This model enables the displacement experiments for surface karst reservoirs, underground river reservoirs, and fault-karst reservoirs, and also the visual analysis of oil-gas-water multiphase flow. The remaining oil distribution before and after nitrogen-assisted gravity drainage (NAGD) was investigated, and the differences in enhanced oil recovery (EOR) for karst reservoirs of different genesis were compared. The results show that NAGD contributes to balanced displacement for karst reservoirs of different genesis, but achieves varying efficiency of EOR - by 12%, 9%, and 7% respectively for fault-karst reservoirs, surface karst reservoirs, and underground river reservoirs. The research findings help to understand the influence of reservoir types on NAGD, providing support to the advancement of EOR techniques for fractured-vuggy reservoirs. Figures and Tables | References | Related Articles | Metrics

Mechanical Mechanism of Karst Cave Collapse in Carbonate Reservoirs ZHANG Jiyue, KANG Zhihong, CHEN Huaxin, KANG Zhijiang 2023, 44 (5):  618-625.  doi: 10.7657/XJPG20230515 Abstract ( 137 )   HTML ( 6 )   PDF (2016KB) ( 92 )   Save To determine the collapse mechanism of karst caves in carbonate reservoirs, through stress field simulation, and based on orthogonal two-dimensional sections of the karst caves, a two-dimensional mechanical model was established to simulate the stress distribution characteristics of the carbonate karst caves under negative pressure. By multiple linear regression on controlling variables, a karst cave collapse model coupling with the stress function of the critical fracture point was constructed to predict the relationships among cave collapse and stress, depth and width. It is found that the most important factors influencing cave rock burst and collapse are overlying formation pressure, reservoir compressive strength and flexural strength. For two caves superimposed vertically, when their vertical distance is less than 0.3 times the cave radius, the partition between the two caves breaks, leading to the cave connection. During the collapse and rupture, the cave height changes obviously, while the width changes slightly. Figures and Tables | References | Related Articles | Metrics

High-Precision Seismic Imaging of Western Qiulitag Structural Belt in Kuqa Depression ZHANG Xiangquan, GU Yongxing, LIU Jun, PEI Jiading, GU Xiaodi 2023, 44 (5):  626-633.  doi: 10.7657/XJPG20230516 Abstract ( 125 )   HTML ( 11 )   PDF (11091KB) ( 90 )   Save The western Qiulitag structural belt is an important successive area for oil and gas exploration in the Kuqa depression, Tarim basin. Its complex surface and underground geological conditions bring challenges to seismic survey. It has been less explored in the main structural belt, where the high steep structural features and complex fault systems cannot be depicted by using previous 2D (single-line and wide-line) seismic data. To address this problem, a combination of wide-frequency band, wide-azimuth and high-density 3D seismic survey and high-density cable 3D seismic survey is used to increase the effective folds in the complex, high, steep structural areas. The microlog-constrained shallow surface velocity modeling is conducted to improve the static correction accuracy in complex mountainous areas and thick gravel-covered piedmont areas. The six-division method for denoising is adopted to improve the signal-to-noise ratio of seismic data in inter-salt and pre-salt structures. The five-dimensional interpolation and regularization technique is applied to mitigate the impact of irregular observation system in mountainous areas on pre-stack depth migration imaging. Moreover, two-way wave reverse time-migration is performed to increase the migration imaging precision of highly steep formations. Through acquisition-processing integration and seismic-geological fusion, the seismic imaging precision in the western Qiulitag structural belt can be significantly improved. Figures and Tables | References | Related Articles | Metrics