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01 June 2022, Volume 43 Issue 3 Previous Issue    Next Issue

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OIL AND GAS EXPLORATION

Practices and Cognitions of Petroleum Exploration in Mesozoic,Ordos Basin LUO Anxiang, YU Jian, LIU Xianyang, JIAO Chuangyun, HAN Tianyou, CHU Meijuan 2022, 43 (3):  253-260.  doi: 10.7657/XJPG20220301 Abstract ( 562 )   HTML ( 31 )   PDF (1437KB) ( 400 )   Save The Ordos basin is the second largest sedimentary basin in China with abundant oil and gas resources and broad exploration prospects. Typical low-permeability-tight oil reservoirs are develpoed in the Triassic Yanchang formation in the basin,which are difficult to explore. Through continously geological researches on the Mesozoic oil reservoirs in the Ordos basin over the past 50 years,some theories about hydrocarbon accumulation in Jurassic reservoir groups,in large-scale lithologic reservoirs in inland depression lake basins and in continental shales have been formed. By virtue of three strategic shifts,four conventional hydrocarbon provinces with reserves exceeding 10×108 t and a successive zone with shale oil reserves of 20×108 t have been discovered. The proven oil reserves have increased by an average of over 3×108 t per year for 10 consecutive years. Thus,Changqing oilfield in Ordos basin has become an oil and gas province with the fastest increase in reserves and production in China and contributed 12.5% of China's annual oil production,which provides a reference for the petroleum exploration in other similar basins. Figures and Tables | References | Related Articles | Metrics

Well Logging Evaluation of Bauxite Reservoirs in Ordos Basin LIU Die, ZHANG Haitao, YANG Xiaoming, ZHAO Taiping, KOU Xiaopan, ZHU Baoding 2022, 43 (3):  261-270.  doi: 10.7657/XJPG20220302 Abstract ( 492 )   HTML ( 21 )   PDF (4208KB) ( 240 )   Save Bauxite gas reservoir is a kind of very rare unconventional gas reservoir recently discovered in the Ordos basin, and well logging evaluation plays an important role in its exploration and development. In the early well logging evaluation, bauxite was considered as the weathering crust caprock, but not as a reservoir, and there was no systematic well logging evaluation method suitable for the exploration and development of bauxite gas reservoirs. Based on the aluminous rocks in Taiyuan formation in the Longdong area, southwestern Ordos basin, the well logging evaluation method for bauxite gas reservoirs was studied from five aspects, that is, qualitative lithology identification, mineral composition, reservoir physical properties, quantitative calculation of gas-bearing properties and systematic summary of imaging model-pore structure characteristics. The well logging response for identifying aluminous rock formations was clarified and the aluminous rock identification chart by acoustic time-gamma ray was established. The porosity-permeability-saturation evaluation model for bauxite gas reservoirs was constructed through petrophysical experiments, and the criteria for identifying bauxite reservoir was proposed by combining micro-resistivity scanning imaging and nuclear magnetic resonance logging data. Finally, a well logging evaluation method for bauxite gas reservoirs was formed. Figures and Tables | References | Related Articles | Metrics

Main Controlling Factors and Gas Enrichment Area Selection of Ma55 Gas Reservoir in Eastern Sulige Gas Field BAI Hui, YANG Tebo, HOU Kefeng, MA Zhixin, FENG Min 2022, 43 (3):  271-277.  doi: 10.7657/XJPG20220303 Abstract ( 370 )   HTML ( 15 )   PDF (5950KB) ( 129 )   Save In order to improve the drilling rate of pay zones in the Ma55 gas reservoir in eastern Sulige gas field, Ordos basin, using the drilling, logging, core and gas production testing data, and analyzing the main factors controlling pay zones such as sedimentary microfacies, diagenesis and paleotopography, the distribution law of dolomite in the Ma55 gas reservoir was clarified. Moreover, the reservoirs were comprehensively classified and evaluated, and the favorable gas enrichment areas in the Ma55 gas reservoir were selected. The research results show that the pay zones in the Ma55 reservoir are distributed as “lens” in local areas, with poor continuity. The most favorable reservoir rocks are granular dolomite and coarse powder crystalline dolomite, and the main storage space consists of intergranular pores, intergranular dissolved pores and structural fractures. Sedimentary facies and diagenesis are the main controlling factors of the Ma55 reservoir, and the grain beach is the most favorable sedimentary microfacies of the Ma55 dolomite. The pay zones are mainly controlled by quasi-contemporaneous dolomitization and buried dolomite diagenesis. The paleoslope on the relatively high position is a favorable area for the development of the Ma55 gas reservoir. Figures and Tables | References | Related Articles | Metrics

Characteristics and Hydrocarbon Generation Potential of Chang 9 Source Rocks on Yishaan Slope, Ordos Basin LUO Lirong, LI Jianfeng, YANG Weiwei, MA Jun, LI Huan, WU Kai 2022, 43 (3):  278-284.  doi: 10.7657/XJPG20220304 Abstract ( 319 )   HTML ( 7 )   PDF (746KB) ( 141 )   Save A number of favorable oil-bearing areas have been discovered in the lower assemblage adjacent to the Chang 9 source rocks on Yishaan slope, Ordos basin. In order to promote the petroleum exploration of the lower assemblage in this area, it is urgent to deepen the research on the characteristics and hydrocarbon generation potential of the Chang 9 source rocks. The distribution of the Chang 9 source rocks were analyzed using well logging, mud logging and core data. The geochemical characteristics and hydrocarbon generation potential of the Chang 9 source rocks were studied by various methods such as rock pyrolysis analysis, total organic carbon analysis, kerogen maceral analysis, and biomarker analysis by saturated hydrocarbon gas chromatography-mass spectrometry. The results show that the Chang 91 source rocks are distributed in Wuqi, Jingbian, Zhidan, Ansai and other areas, with the maximum thickness of over 20 m, and the Chang 92 source rocks are mainly developed in Ganquan-Luochuan area, with the maximum thickness of over 12 m. The Chang 9 source rocks hold a high abundance of organic matters that were originated from lower aquatic organisms and terrestrial higher plants. With Type Ⅰ and Ⅱ1 organic matters in dominance, which are in the mature stage, the Chang 9 source rocks exhibit high hydrocarbon conversion rate and especially strong hydrocarbon generation capability in Zhidan-Ansai area. The Chang 9 source rocks are mostly good and locally high-quality rocks with strong hydrocarbon generation and expulsion capacities, which provides a material basis for hydrocarbon accumulation in the lower assemblage of Yanchang formation on Yishaan slope. Figures and Tables | References | Related Articles | Metrics

Reservoir Characteristics and Controlling Factors of Shan 1 Member in Qingyang Gas Field, Ordos Basin DUAN Zhiqiang, XIA Hui, WANG Long, GAO Wei, FAN Qianqian, SHI Wei 2022, 43 (3):  285-293.  doi: 10.7657/XJPG20220305 Abstract ( 324 )   HTML ( 8 )   PDF (6467KB) ( 138 )   Save In the Qingyang gas field, Ordos basin, which is a typical tight sandstone gas field, the major pay zone is the first member of the Permian Shanxi formation. Its sedimentary sand bodies change rapidly with small thickness, making the prediction of reservoir distribution difficult, which restricts the productivity construction of the gas field. In this paper, sedimentary sand body characterization and thin layer prediction were carried out using logging-seismic combination, the main factors controlling reservoir development were discussed, and favorable reservoir distribution areas were identified. The results show that the paleogeomorphology and paleo-flow direction jointly controlled the distribution of delta sand bodies, the underwater distributary channel sand bodies with developed dissolution facies are the most favorable reservoirs, and the local micro-amplitude nose uplift structure is the natural gas enrichment area. Based on the factors such as sand body distribution, reservoir physical properties, diagenesis and structural characteristics, a set of standards for classifying reservoirs in the study area was established, by which two Type I reservoir enrichment areas were defined in the southern and central parts of the study area. Figures and Tables | References | Related Articles | Metrics

Sand Body Architecture of Chang 9 Member in Jiyuan Area,Ordos Basin WU Zemin, KE Xianqi, ZHANG Pan, WEN Fengqin, TONG Qiang, LIU Linyu 2022, 43 (3):  294-309.  doi: 10.7657/XJPG20220306 Abstract ( 263 )   HTML ( 3 )   PDF (6534KB) ( 193 )   Save In order to clarify the spatial configuration of sand bodies under the dual-provenance background in Chang 9 member in Jiyuan area,Ordos basin,the sedimentary characteristics of Chang 9 member were determined by using the core,logging,test and production data. On this basis,the sand body architecture of Chang 9 member was dissected level by level to understand the development of sand bodies under the dual-provenance background and to characterize the architectural elements and their assemblage and distribution. The results reveal that there are 8 types of skeleton architectural elements in Chang 9 member,which are different from region to region: braided channel,abandoned channel and cross-bank deposits dominated by underwater distributary channel and interdistributary bay in the west; and estuary sand bar,front sheet sand and underwater natural levee in the east. On the plane,the architectural element of braided channel extends farther with continuous distribution,the architectural element of abandoned channel extends shortly with intermittent distribution,the architectural element of underwater distributary channel extends farther with discontinuous distribution,and the architectural element of estuary sand bar is usually in the side rear of the underwater distributary channel with poor continuity. Vertically,the superimposition and assemblage of the architectural elements of skeleton sand bodies become worse from bottom to top,and the architectural elements of braided river delta system in the west display better development scale and degree than those of meandering river delta system in the east. Figures and Tables | References | Related Articles | Metrics

Sedimentary Characteristics and Sand Body Architecture of Shallow Delta Front in Ordos Basin: A Case Study of Chang 9 Member in Shiwanghe Section in Yichuan REN Yilin, ZHAO Junfeng, CHEN Jiayu, GUAN Xin, SONG Jinggan 2022, 43 (3):  310-319.  doi: 10.7657/XJPG20220307 Abstract ( 362 )   HTML ( 8 )   PDF (5476KB) ( 237 )   Save As an important reservoir for storing oil and gas,the sand bodies in delta front are found with enormous petroleum exploration potential. However,there are few studies on architecture of sand bodies in shallow delta front through field outcrops. Guided by sedimentology and reservoir architecture theories,the outcrop observation and sampling was combined with the results of laboratory experiments and statistical analysis to clarify the sedimentary characteristics and sand body architecture of Chang 9 member in the Shiwanghe section in Yichuan,Ordos basin. The results show that during the deposition,the Chang 9 member in Shiwanghe section lied in a warm and humid environment,especially an oxidation to weak-reduction transitional freshwater environment that was not obviously stratified,and shallow delta front subfacies was mainly developed,including microfacies such as underwater distributary channel,estuary bar,sheet sand and interdistributary bay. The single sand bodies of shallow delta front in Chang 9 member in the study area can be divided into two vertical stacking styles such as non-connected and connected,and two lateral contact styles such as butted and cut-stacked. The accommodation growth rate and sediment supply rate jointly controlled by terrain slope and lake level rise/fall are important factors affecting the spatial development style of the composite sand bodies. The gentle slope allows the channels to incise weakly and present the characteristics of plane intersection. The rise of lake level and the decrease of source supply increase the ratio of accommodation growth rate to sediment supply rate,which may lead to the weakening of sand body connectivity. The architecture models of sand bodies like river-river cut stacking and river-bar cut stacking are favorable for hydrocarbon accumulation. Figures and Tables | References | Related Articles | Metrics

RESERVOIR ENGINEERING

Reservoir Benefit Classification and Development Countermeasures for Changqing Oilfield ZHOU Xiaoying, WEI Mingxia, ZHANG Yirong, LI Ting, XU Sen 2022, 43 (3):  320-323.  doi: 10.7657/XJPG20220308 Abstract ( 278 )   HTML ( 7 )   PDF (464KB) ( 190 )   Save Influenced by the increasing reservoir types in Changqing oilfield and the low international crude oil price, clarifying the benefit categories of reservoirs and identifying the oil production limits of different types of reservoirs under different oil prices are urgent for Changqing Oilfield Company to make production and operation decisions. By combining the benefit evaluation with reservoir research, dynamic development, well production failure and comprehensive treatment, the relationship between cost or development index and benefits for different types of reservoirs was established, and the influencing factors of low-benefit wells were analyzed, providing a reference for cost-effective development of reservoirs. Figures and Tables | References | Related Articles | Metrics

Establishment and Application of a Combined Production Decline Prediction Model for Tight Sandstone Gas Well LI Xiaofeng, XU Wen, LIU Pengcheng, YUE Jun 2022, 43 (3):  324-328.  doi: 10.7657/XJPG20220309 Abstract ( 262 )   HTML ( 5 )   PDF (602KB) ( 160 )   Save The Permian fluvial sandstone gas reservoirs in the Sulige gas field are tight and contain effective sand bodies that are mostly isolated or banded. After gas wells are put into production, reservoir fluid stays consistently in an unsteady flow state, and it is late to reach the boundary-dominated flow state. In this case, the traditional Arps production decline analysis method is not sufficient for field application. This paper analyzed the causes for the poor adaptability of the Arps production decline analysis method. On this basis, the variation law of the decline exponent of wells in tight gas reservoirs was identified by numerical simulation, and the relationship between the decline exponent and the flow period of fluid in gas wells was clarified. Finally, it was proposed to use the channel linear flow model to predict the production in the unsteady flow period and the Arps model to predict the production in the boundary-dominated flow period. For the gas wells in the unsteady flow period, the critical point time to attain boundary-dominated flow is determined by the theoretical formula; in the boundary-dominated flow period, the time of inflection point deviating from the linear flow is the critical point time. The field application shows that the proposed combined production decline model is accurate and effective in predicting the decline characteristics and indicators of gas wells. Figures and Tables | References | Related Articles | Metrics

Production System of Horizontal Well in Shale Oil Reservoirs of Chang 7 Member, Ordos Basin WAN Xiaolong, ZHANG Yuanli, FAN Jianming, LI Zhen, ZHANG Chao 2022, 43 (3):  329-334.  doi: 10.7657/XJPG20220310 Abstract ( 213 )   HTML ( 6 )   PDF (3813KB) ( 192 )   Save To ensure the production of shale oil in Chang 7 member, Ordos basin, this paper discussed the production system of the horizontal well in Chang 7 member based on the theoretical research and production data. By establishing the relationship between the distance of the pressure propagation boundary from fractures induced by volume fracturing in horizontal well and the time, and assuming that the pressure propagated to the boundary does not change with time, the reasonable well soaking period is determined to be 40 d. It is considered that the high-watercut drainage stage ends when the analyzed salinity of the produced water is similar to the salinity of initial formation water, or the replacement rate of fracturing fluid in horizontal wells is greater than 60%. By quantitatively analyzing the production profile of a single section and a 100-m horizontal section in the horizontal well, the dynamic relationship was established for determining a reasonable fluid production for each stage. Figures and Tables | References | Related Articles | Metrics

Upper Limit of Water Saturation for Profitable Development of Tight Sandstone Gas Reservoirs in Sulige Gas Field XIAO Feng, YUE Jun, LI Zhichao, LIU Lili, ZHANG Ji, FAN Jiwu, ZHANG Tao 2022, 43 (3):  335-340.  doi: 10.7657/XJPG20220311 Abstract ( 261 )   HTML ( 2 )   PDF (634KB) ( 159 )   Save In the Sulige gas field, tight sandstone gas reservoirs present a high water saturation. The water cut increases rapidly after the gas wells are put into production. With the increase of water cut, the production of gas wells declines greatly or even stops. Based on the analysis of production performance of water-producing gas wells, the relationships between the water saturation and the cumulative gas production and recovery rate of the gas wells were established. Combined with the single well investment and natural gas price, the minimum cumulative gas production required to recoup the investment in a gas well was determined, and accordingly the upper limit of reservoir water saturation was determined. Furthermore, taking the minimum cumulative gas production of gas wells as the standard, and considering the reservoir water saturation and reservoir thickness, the quantitative indicators for the logging interpretation of gas layers, gas-water layers and gas-bearing water layers were determined. The results show that the upper limit of water saturation of tight sandstone reservoirs in the central part of Sulige gas field is 48.2%, and when the economic minimum cumulative gas production in the life cycle of a gas well reaches 1 260×104 m3, the gas well is profitable. Figures and Tables | References | Related Articles | Metrics

Production Profile of Horizontal Wells in Strongly Heterogeneous Tight Gas Reservoirs in Sulige Gas Field FAN Jiwu, XU Zhenping, LIU Lili, ZHANG Juan 2022, 43 (3):  341-345.  doi: 10.7657/XJPG20220312 Abstract ( 271 )   HTML ( 7 )   PDF (1499KB) ( 134 )   Save In order to determine the productivity of each fracturing section of a horizontal well after staged fracturing in the Sulige gas field, the production profile of horizontal wells and its influencing factors such as reservoir heterogeneity, flow characteristic, multistage fracturing technique and production pressure difference were analyzed. It is found that physical properties of reservoirs and development degree of effective sand bodies are the main factors controlling gas well productivity, and they have greater effect than the flow dominant term at the heel and toe of the horizontal well in an ideal model. The increase in production pressure difference aggravates the difference in gas production rate among fracturing sections in strongly heterogeneous reservoirs. The uneven distribution of induced fractures leads to different gas productivities of perforation clusters in the same fracturing section. Therefore, for multi-stage fractured horizontal wells, technical countermeasures such as optimization of perforation sections, differential stimulation of horizontal sections, and uniform fracture propagation by temporary plugging were proposed so as to improve the development effect of tight gas reservoirs. Figures and Tables | References | Related Articles | Metrics

Influencing Factors and Prediction Methods for Production of Tight Oil Reservoir in Pingbei Oilfield HU Xinling, WANG Jian, PAN Lin 2022, 43 (3):  346-353.  doi: 10.7657/XJPG20220313 Abstract ( 284 )   HTML ( 6 )   PDF (599KB) ( 156 )   Save Compared with conventional oil reservoirs, tight oil reservoirs have poor physical properties and low permeability, and wells drilled in these reservoirs need to be fractured for more production. Due to the geological features and special development techniques, there are many factors affecting the production of these reservoirs, and the simple analogy method commonly used on site for production prediction cannot meet the actual needs. In order to solve this problem, taking the tight oil reservoir in Pingbei oilfield of Ordos basin as the research object and based on the Darcy equation, the main influencing factors for production were quantitatively described through grey theoretical analysis. Moreover, a mathematical model was established by using the multiple regression method, and applied to predict the production of new wells in order to verify the reliability of the model. Production prediction by using the multidisciplinary method that combines the grey theory and multiple regression is more scientific and accurate than by using traditional methods, and it can provide a reference for the development of similar oil reservoirs. Figures and Tables | References | Related Articles | Metrics

APPLICATION OF TECHNOLOGY

Evaluation on Adaptability of Horizontal Well Development to Multi-Layer Tight Sandstone Gas Reservoirs LIU Jiaojiao, WANG Delong, LIU Qian, TANG Jing 2022, 43 (3):  354-359.  doi: 10.7657/XJPG20220314 Abstract ( 281 )   HTML ( 5 )   PDF (962KB) ( 121 )   Save For multi-layer gas reservoirs in the Shenmu gas field, improper selection of geological targets for horizontal well development may lead to the problems such as poor economic benefits and unrecovered reserves. The development scale and stacking patterns of sand bodies in these multi-layer gas reservoirs were investigated, and the single-layer, double-layer and multi-layer gas reservoir models were established by adopting the concept of reserves concentration. Taking the horizontal well stimulation ratio as the basis for economic benefit evaluation, the reservoir limit of horizontal well development in multi-layer reservoirs was evaluated. The research shows that large-scale composite effective reservoirs are locally developed in the Lower Permian Taiyuan formation and the second member of the Lower Permian Shanxi formation in the Shenmu gas field, with an effective thickness of 6.0-9.0 m and a length of 1 600-3 200 m. These intervals satisfy the optimal reservoir conditions for horizontal well development, namely the reserves concentration greater than 75% and the permeability ratio of the dominant layer to the secondary producing layer ranging from 0.8 to 3.9. Figures and Tables | References | Related Articles | Metrics

Method for Calculating Single-Well Producing Geological Reserves and Single-Well Technically Recoverable Reserves in Tight Sandstone Gas Reservoirs: A Case of Carboniferous-Permian Gas Reservoirs in Yanchang Gas Field, Ordos Basin CHEN Zhanjun, REN Zhanli 2022, 43 (3):  360-367.  doi: 10.7657/XJPG20220315 Abstract ( 298 )   HTML ( 12 )   PDF (711KB) ( 153 )   Save The Carboniferous-Permian sandstone gas reservoirs in the Ordos basin are tight, with obvious different gas saturations from part to part of the reservoir unit, complex gas-bearing pattern, non-uniform reservoir pressure systems, and highly heterogeneous distribution of reserves as a whole. This paper compared the geological and development characteristics between Carboniferous-Permian tight sandstone gas reservoirs and the conventional sandstone gas reservoirs in Yanchang gas field in Ordos basin. It is found that there is a threshold pressure gradient during the development of the Carboniferous-Permian tight sandstone gas reservoirs, and the single-well produced geological reserves and the single-well reserves producing radius increase with the decrease of the bottom hole pressure. When the abandonment pressure is reached, the single-well produced geological reserves and the single-well reserves producing radius reach the maximum values. Accordingly, by analyzing the distribution of reserves during the development of tight sandstone gas reservoirs, the material balance equation under the condition of threshold pressure gradient was established, and the relationship between cumulative production and bottom hole pressure was obtained. Furthermore, two methods for calculating the threshold pressure gradient were analyzed. On this basis, the method for calculating the single-well producing geological reserves and the single-well technically recoverable reserves in tight sandstone gas reservoirs was proposed, which provides a theoretical basis for the optimization of well pattern to develop tight sandstone gas reservoirs. The theoretical calculation method has been improved to form a simplified method for calculating single-well producing geological reserves, which is referential for well pattern deployment in undeveloped blocks. Figures and Tables | References | Related Articles | Metrics

Technologies and Application of Sidetracking Horizontal Well in Existing Wells in Sulige Gas Field WANG Liqiong, WANG Zhiheng, MA Yulong, ZENG Qingxiong, ZHENG Fan 2022, 43 (3):  368-377.  doi: 10.7657/XJPG20220316 Abstract ( 275 )   HTML ( 7 )   PDF (1058KB) ( 210 )   Save In order to improve the effective reservoir encounter rate during sidetracking drilling in existing wells,with a block in central Sulige gas field as an example,and combined with the geological characteristics and development status of the gas field,the key geological technologies for sidetracking horizontal drilling in existing wells were summarized from the aspects of optimal deployment and geosteering. On this basis,the development effect of sidetracking horizontal wells was discussed in light of drilling effect,production index,benefit evaluation,etc.,and the influence of various factors on the development effect was comprehensively analyzed. The research results show that the remaining gas mainly enriches in the areas including the rim of mid-channel bar,braided channel,and middle or bottom of the mid-channel bar in the sand belt of main channel. Based on the economic evaluation,the selection criteria for sidetracking well locations were established,that is,the lower limit of the effective thickness of recoverable beds is 4 m vertically,and the lower limit of the abundance of the remaining reserves is 0.42×108 m3/km2 on the plane. Using 3D geological model,stratigraphic dip evaluation,pilot hole information and data acquired while drilling,the horizontal-well geosteering sidetracking technology was formed,and three horizontal-section geosteering modes were provided. For 23 sidetracking horizontal wells in the study area,the average effective reservoir encounter rate is 59.7%,the average initial gas production is 2.9×104 m3,and the cumulative incremental production is 3.13×108 m3. Figures and Tables | References | Related Articles | Metrics