In recent years, optical fiber distributed temperature sensor system (DTS) has been increasingly used in horizontal well fracturing dynamic monitoring, aiming to solve the technical problems commonly faced in the process of horizontal well fracturing, such as artificial fracture initiation location unknown, fracturing fluid whereabouts unknown, fracture propagation morphology unclear, fracturing effect difficult to evaluate. The temperature prediction model is the basis of fracturing diagnosis based on DTS monitoring, but it is still a great challenge to predict quantitatively the temperature distribution in the fracturing process of horizontal wells. Considering the basis of a variety of trace heating effect, this paper established a set of horizontal well staged fracturing temperature distribution prediction model and completes the solution coupling model. The established temperature model was used to simulate the temperature distribution of conventional fracturing and multistage fracturing in a horizontal well, and the temperature distribution characteristics in the process of multistage fracturing were analyzed. The effects of fracturing fluid displacement, formation filtration coefficient, fracture width and fracture height on temperature distribution were determined. The research results provide theoretical support for the realization of DTS based monitoring and diagnosis of fracturing performance, identification of fracture initiation and analysis of fracturing fluid direction, which is of great significance for the evaluation of fracturing effect and fracturing design optimization of fractured horizontal wells.
As an important characteristic of shale oil and gas reservoir, bedding has a significant influence on vertical propagation of hydraulic fractures. Through theoretical analysis, innovation of large-scale hydraulic fracturing simulation experiment method, and field scale hydraulic fracture monitoring for shale oil and gas reservoirs, the vertical fracture propagation patterns under bedding condition are revealed, and the main controlling factors of fracture penetration are identified, which could guide the optimization of unconventional reservoir treatment. The experiments indicate that there are three different kinds of results when the fracture height reaches the bedding plane: crossing directly, crossing offsets and arresting (bedding slippage or dilation). Besides, the orthogonal analysis shows that the bedding strength is one of the most critical influences on fracture height. The field practice further confirms that weak bedding plane can arrest fracture height obviously and the fracture height also can cross the bedding because of strong bedding interface. In addition, the natural fractures on the plane and the difference of mechanical properties between layers also have significant influence on the fracture height. The research can provide technical support for the optimization design of hydraulic fracture vertical propagation under the bedding existence in unconventional reservoir.
Taking Deng 4 Member gas reservoir of Sinian system in central Sichuan Basin as an example, aiming at the main problems of the controlling factors of productivity and development strategies optimization in the early and middle stages of the highly heterogenous gas reservoir，the scientific connotation of the controlling factors of gas well productivity was studied，and the core elements and main research items of the controlling factors of productivity in different stages were put forward. Based on the six types typical seepage patterns of gas reservoirs, the early, transitional and stable stages were defined. On this basis, the countermeasures and suggestions were given in four aspects: Well location plane deployment, target location, transformation process and production well system optimization. The results show that: (1) The controlling factors of productivity refer to the main conditions that affect the productivity of gas wells, and the research objects and emphases are different in different development stages. The core elements are the implementation of reserve base, the seepage capacity of transformation area and far well area, and the main research items are the key indicators of high-quality reservoirs, seismic response, special well test interpretation technology, etc. (2)The regular production capacity of the early stage, transitional and stable stages of Deng 4 Member gas reservoir is controlled by the development of high-quality reservoir，the matching of fracture system after reservoir transformation，the gas supply capacity of far well area and the remaining dynamic reserves. And the influence of the electrical characteristics of high-quality reservoir, the characteristics of well test after transformation, construction curve, the plane heterogeneity and the variation of remaining dynamic reserves on the production capacity at different stages in the early and middle stages are clarified. (3)Through the implementation of development strategies optimization, the breakthrough of single well production has been achieved. The average absolute open flow rate of the new technology well were 2.3 times of the vertical well, the proportion of stable production increased from 80.5% to 95%, and the tubing pressure decline rate slowed down, which basically met the design requirements of the development scheme. The research results from the controlling factors of productivity in the early and middle stage and the development optimization technical countermeasures provide technical reference for the efficient exploration and development of ultra-deep strong heterogeneity carbonate gas reservoirs.
Large-scale of petroleum accumulations are continuously discovered in deep marine carbonates with depth over 7000 m in the cratonic area of the Tarim Basin, however, the research on the petroleum accumulation needs further enhancement due to the complex geology and evolution characteristics. Ultra-deep oil pools were discovered within an interval of 7 100-7 600 m in the Yueman area, which is located in the slope area of the southwestern Tabei Uplift. Based on the comprehensive geological-geochemical analysis of these oil pools, the favorable conditions for the accumulation of deep petroleum were unraveled. The major faults on the one hand controlled the karstification of carbonates and led to the development of fault-karst carbonate reservoirs in the Yijianfang Formation, and thus formed favorable reservoir-seal assemblage in combination with the overlaid valid seals from the Tumuxiuke and Sangtamu formations; on the other hand, the major faults served as favorable migration pathways for the deep fluids, especially for the migration of oil and gas from the deep Cambrian-Ordovician source rocks. Under the background of both relatively low geothermal gradient and rapid burial process during the late period after petroleum accumulation, the petroleum did not undergo cracking and remained in the single liquid phase due to the insufficient compensation of temperature with heating time. It can be therefore indicated from the petroleum accumulation process in the Yueman area that, there remains great potential for liquid petroleum exploration in deep strata, and the future exploration targets should be the fault-karst carbonate reservoirs with strong bead-like reflections.
The first Member of Maokou Formation has great potential for gas exploration，but the problem of unclear understanding of sedimentary facies always exists. Based on the fine centimeter-level description of two latest drilling cores in central Sichuan Basin and multiple field outcrop observations, combined with the analysis of laboratory data and logging curves，a detailed analysis of sedimentary facies markers is carried out, and a new sedimentary facies division plan of the first Member of Maokou Formation is proposed. The main difference between eyeball-shaped limestone and eyelid-shaped limestone lies in the amount of argillaceous content, and natural gamma curve can effectively distinguish these two lithofacies. The marine anoxic environment, a large number of storm sedimentary structures and siliceous bioclasts indicate that the first Member of Maokou Formation was deposited in a ramp carbonate platform environment and was affected by storm action and associated storm upwelling. Based on the facies markers，the first Member of Maokou Formation is divided into two subfacies：The outer belt of middle ramp and the upper part of outer ramp. The outer belt of middle ramp includes three microfacies: Storm debris flow, storm beach, storm inter beach depression. The upper part of outer ramp has relatively high content of eyelid-shaped limestone, the microfacies combination is particle flow and static mud intercalated debris flow, which generally develops in the upper part or the top of the first Member of Maokou Formation.
Thermal evolution and hydrocarbon generation history of source rock, reservoir diagenesis and physical property evolution history, structural trap and migration system formation and evolution history are simulated and studied through comprehensive application of basin simulation, structural evolution analysis, temperature measurement of fluid inclusions in the Western Sichuan gas field. And the matching relation of the spatial evolution of each condition for gas accumulation is further analyzed. Results show that the dolomite reservoir of the third sub-member of the fourth Member of Leikoupo Formation(Lei43) was already formed in the (quasi) contemporaneous period, the anticline traps, such as Shiyangzheng, Jinma and Yazihe, were formed in the late Indosinian tectonic movement. The faults such as Guankou and Pengzhou and the unconformity surface at the top of the Leikoupo Formation form a continuous and smooth vertical and horizontal oil and gas migration system through the Dongwu movement, Indosinian movement, early Yanshan tectonic movement. The formation time of these accumulation conditions is early and the spatial configuration relationship is good, which provides a good hydrocarbon accumulation migration channel and storage space. Based on the thermal evolution and hydrocarbon generation history of source rocks of Longtan Formation of the Upper Permian series and Leikoupo Formation of the Middle Triassic, the gas reservoir has undergone multiple stages of evolution. Formation of the third sub-member of the fourth Member of Leikoupo Formation(Lei43) gas reservoir experienced the process of late Indosinian to early Yanshanian paleo-reservoir oil cracking, oil supply from source rock of Leikoupo Formation and gas supply from ancient reservoir cracking in the Yanshan epoch. The gas reservoir was finally formed in the late Yanshanian-Himalayan period.
Linxing area is located in Jinxi flexural structural belt, eastern margin of the Ordos Basin, China. The gas reservoir of Shangshihezi Formation is widely developed in this area. Based on reservoir rock characteristics analysis, basin simulation technology and fluid inclusions test, combined with regional structural evolution, well logging, gas production test and other relevant data, the geological conditions and reservoir formation characteristics were studied and the main controlling factors of gas enrichment of Shangshihezi Formation in Linxing area were discussed. Results show that the coal seam began to generate hydrocarbon and pressurized in the Early Jurassic with long duration and high residual pressure, which provides the dynamic conditions for gas charging; the maximum burial depth of the Shangshihezi Formation is relatively shallow, and the reservoir is in the middle diagenesis stage A with low densification degree. The reservoir physical property is characterized by ultra-low permeability gas reservoir, which is conducive to the migration and accumulation of natural gas. In addition, lack of abnormal high pressure barrier provides a convenient condition for the gas upward migration. It is considered that the gas reservoir of Shangshihezi Formation formed earlier than the eruption of Zijinshan volcanic, and the gas reservoir is a result of long-term continuous charging, densification and accumulation occurred simultaneously. Results of exploration and development show that gas enrichment is significantly affected by the distribution of favorable sand and the paleotectonics during accumulation period.
The Upper Paleozoic in the eastern Ordos Basin are rich in oil and gas resources, showing great potential. In recent years, the effectiveness of cap plays a key role in gas accumulation with the deepening research in this area. Based on logging, core data, a logging model for the breakout pressure of the Upper Paleozoic cap rock in the eastern Ordos Basin was built. By applying this model, the spatial distribution and breakthrough pressure distribution of the Upper Paleozoic cap in the eastern Ordos Basin were studied, which reveals the controlling factors of cap rock sealing ability. By integrating production data, the comprehensive evaluation of rock sealing ability was discussed. The results show that there are three sets of mudstone caps in the Upper Paleozoic in the eastern Ordos Basin: The Shiqianfeng Formation, the Shangshihezi Formation and the Shanxi Formation. The cap in Shiqianfeng Formation is the thickest with wide distribution, and is in the middle diagenetic A stage. The mudstone has high plasticity and good toughness, showing the relatively high breakthrough pressure and good sealing performance, which is regional cap. The Shangshihezi Formation cap is between the middle diagenetic A stage and B stage. However, the pure mudstone is relatively thin due to the frequent interbedded of argillaceous siltstone and fine sandstone. Therefore the breakthrough pressure is the lowest, leading to the worst seal ability. The cap at the top of the Shanxi Formation is the thinnest, however, it is in the middle diagenetic B Stage due to the deepest burial depth, and the mudstone plasticity is enhanced, therefore the breakthrough pressure is the highest and the capping ability is the best.
In order to clarify the characteristics and classification of Chang 8 Member reservoir in Anbian area of Ordos Basin， and provide basic geological basis for exploration and development in Anbian area， this study obtained the following results by comprehensively using particle size analysis， vacuum immersion casting thin slices， scanning electron microscope， mercury injection method， clay mineral X-ray diffraction method and conventional physical property analysis， combined with core observation and logging data for macro verification. The results show that： the sandstone types of Chang 8 Member reservoir in the area are mainly fine-grained feldspar sandstone and lithic sandstone with low maturity； the carbonate cement is mainly iron calcite； among the clay mineral interstitials， the content of Chang 81 sub-member illite is the highest， while the Chang 82 sub-member is mainly chlorite； the storage space is mainly residual intergranular pores and feldspar dissolved pores； the destructive diagenesis that affects the quality of the reservoir is mainly compaction and cementation， and the constructive diagenesis is dissolution. Statistical results of physical properties indicate that the Chang 8 Member reservoir is a low porosity， low permeability-extra-low permeability reservoir. According to the classification and evaluation criteria， Chang 8 Member reservoir in Anbian area is divided into four types. The favorable exploration and development areas are mainly type I and type II reservoirs， which are distributed in a long strip from northeast to southwest and belong to the main part of underwater distributary channel； The optimal reservoir of Chang 82 sub-member is mainly located in the middle of Anbian area， and the optimal reservoir of Chang 81 sub-member is mainly located in the east of Anbian area.
The Ma'nan area is located in the southwest part of the Mahu Sag in the Junggar Basin. Based on the total organic carbon content (TOC), Rock-Eval pyrolysis, core, rock thin section and fluorescence chip, the authors contrast the organic geochemical characteristics and effectivity of the second and the third members source rocks of the Fengcheng Formation in the study area. The Fengcheng Formation source rock samples from the boreholes were sampled from the second and the third members. There are higher oil-generating capability and potential and in the second than in the third member. Depending on maturity parameters and their influencing factors, the source rock was thought in the mature oil-generating stage. Because of differences of organic matter type and hydrocarbon-generating capability, the low limit value of the second member TOC of the Fengcheng Formation is 0.7% and 2% for the third member. Because of soluble organic matter and TOC content influence, it should be careful to analyze the thermal evolution characteristics of source rocks by using Rock-Eval Tmax. The Fengcheng Formation source rock may not only hydrocarbon accumulation outside source rock layer but also shale oil resource inside the source rock layer.
The transport of shale gas through porous media can be affected by diffusion， advection， and adsorption-desorption， and the isotopic molecules of methane （13CH4， 12CH4） are different in adsorption affinity and diffusion coefficients， so carbon isotope fractionation occurs with these processes. In order to clarify the mechanism of carbon isotope fractionation in methane transport， one-dimensional flow-through experimental device and on-line isotope monitoring method are developed. By means of the carbon isotope fractionation comparison experiment of methane passing through illite-packed column and the empty column， the diffusion effect caused by concentration gradient in the process of methane flow being the important factor of isotopic fractionation are demonstrated. An analytical solution of coupled advection-diffusion equation is developed to fit well the carbon isotope data and interpret the results from each experiment of empty column. In the experiments of illite packed column， it is found that the carbon isotopes of methane in the initial stage are significantly negative shift compared with the original value， and then the carbon isotope compositions of methane rapidly become heavier， and the maximum relative value relative to the original value can reach 5‰. After then the carbon isotopes of methane becomes lighter gradually to the original values. It is found that the curve of isotope composition change shows an obvious inflection point， which are affected by the combination result of diffusion and adsorption-desorption. It also reveals that methane acts on the adsorption sites of solid molecular sieves in the process of flow， showing obvious reverse isotope effect. This is the result of the interaction of diffusion and adsorption-desorption， and it reveals that methane has an obvious inverse isotope effect over the adsorption sites of molecular sieves in the transport.
Based on the geochemical analytical data of Wells Baye-1, Baye-2 and Baye-3 in the Triassic Babaoshan Formation in the East Kunlun area, the redox conditions, paleo-salinity, paleo-climate and paleo-water depth, are reconstructed. The results show that the V/(V + Ni) and Cu/Zn are 0.6-0.84 and 0.21-0.63, respectively, with La/Ce>1.8, Sr/Ba<0.5, B/Ga<3, and Sr/Cu=1-10. The proxies indicate that the paleowater depth should be more than 15 m, and the sedimentary environment was a marine-continental transitional facies-continental facies with oxygen-deficient, warm and humid, brackish water-fresh water. The contents of rare earth elements are high, with light rare earth elements enriched, but deficient in heavy rare earth elements. The distribution curves of rare earth elements are parallel with each other and present an obvious right-leaning V shape. The Eu is a positive anomaly, whilst Ce is a weak negative anomaly. These proxies indicate that the sedimentary environment was weakly reduced.
Microfractures at the Ziliujing lacustrine shale at Fuling area in eastern Sichuan Basin were investigated via core observation, SEM image observation and high pressure mercury injection, and the contribution of microfracture development to reservoir capacity was quantitatively discussed. The following understanding is obtained: (1) Fracture types in lacustrine shale reservoir are defined; (2) The contribution of fractures to lacustrine shale reservoir is determined. Results show that the microfractures in the Lower Jurassic Ziliujing lacustrine shale reservoirs in eastern Sichuan Basin can be divided into three types with four groups: Microfractures related to sedimentation (bedding fractures), microfractures related to diagenesis (clay?mineral shrinkage fractures) and microfractures related to hydrocarbon generation (organic?matter shrinkage fractures and organic?matter?cracking fractures). High pressure mercury injection and plane porosity determination confirm that microfractures in lacustrine shale reservoirs have good reservoir performance, whose contribution to shale reservoir capacity is about 25%.
Deep shale gas (3 500-4 500 m) is the important replacement field of shale gas production growth in China in the future. Research on the key characteristics of deep shale gas reservoirs is the key to clarify their basic geological characteristics and establish a suitable development method. In order to clarify the characteristics and controlling factors of the adsorbed gas in the deep shales of the Longmaxi Formation, comprehensive analysis tests such as high-pressure methane adsorption, low-temperature nitrogen and carbon dioxide adsorption were carried out, and adsorption model fitting and comparative analysis were conducted. The results show that the adsorption isothermal curves of deep shales also have a downward trend when the pressure is high, and the adsorption characteristics have no obvious change. This is mainly due to the lack of microscopic pore structure characteristics of deep shale and middle-deep/middle-shallow shale. The comparative analysis of three commonly used adsorption models shows that different adsorption models can well fit the adsorption curve of deep shale, but the absolute adsorption capacity after conversion shows the same law: DA-LF model > DR model > Langmuir model. Combined with the analysis of the correlation between the pore structure and the amount of adsorbed gas, it is believed that the DR model based on micropore packing is more suitable for characterizing the adsorption law of deep shale. Through correlation analysis, it is believed that TOC is the key material factor that controls the adsorption of deep shale gas, and the specific surface area of ??micropores is the key space factor. Compared with middle-deep/middle-shallow shale, deep shale has higher siliceous content, lower calcite content, lower TOC content, and lower adsorbed gas. The proportion of adsorbed gas is only about 30%.
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