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The reservoir depth of T-Sh oilfield in Tarim Basin is more than 7500 m, which is a typical deep carbonate fault-controlled reservoir. The S-1 and S-5 fault zones experienced multi-stage tectonic movements and developed complex fault-fracture systems. Based on geometry and dynamics, the evolution characteristics of faults are analyzed; the permeability of strike-slip faults in the middle and lower Ordovician carbonate strata drilled through in S-5 fault zone is studied by comprehensively using core observation, imaging logging, 3D seismic data, and drilling historical data, taking wells F-1 and F-10 as examples. It is found that the fault-fracture system is the main reservoir space and fluid migration channel in the reservoir. A large mud loss will occur when drilling high permeability faults. High production can be obtained after conventional well completion, otherwise, it is difficult to get production. In this paper, slip tendency coefficient is used to quantitatively characterize the permeability of fractures in T-SH ultra-deep reservoir. Based on the one-dimensional geomechanical model and three-dimensional geological structure model of typical wells, the slip tendency coefficients of different parts of the fault-fracture system are calculated using finite element numerical simulation method. Compared with the historical data of drilling in S-1 and S-5 fault zones, it is found that the slip tendency coefficient is positively correlated with mud loss. The results show that the critical slip tendency coefficient of the S-5 fault zone is 0.3, and that of the S-1 fault zone is 0.2. This study provides a new idea and method for the prediction of geological desserts and well trajectory design in the T-Sh reservoir. [ABSTRACT FROM AUTHOR]

Petroleum stability varies greatly among different basins with light oil recently being produced from reservoirs at depths up to 8260 m and present bottom hole temperatures up to 171 °C in the Tarim Basin. Determining the extent of oil-gas conversion (EOGC) and its controls are crucial to the "exploration deadline" of temperature or depth for liquid hydrocarbons. For this purpose, about 90 oils from the Cambrian and Ordovician in the Tarim Basin have been analyzed for biomarkers, diamondoids and thiadiamondoids, and their gas/oil ratios were collated. These oils have EOGC from 45.4 to 98.3% for TSR-altered oils in the Tazhong and Shunbei areas, and only 0–49.2% for all other non-TSR oils. Among non-TSR-altered oils, Tazhong oils show higher EOGC values (28.0–49.2%) than those in Tabei (0–9.7%) and Shunbei (0–32.7%) oils, respectively. We propose that higher heating rates (7 °C/Ma) and shorter durations (<5 Ma) at high temperatures (>150 °C) may account for the lower EOGC values of oils in the Tabei and Shunbei areas than those in the Tazhong with values of 0.1 °C/Ma and 250 Ma (>120 °C), respectively. The oil may be completely converted to methane-dominated gas if it was exposed to high temperatures for a longer duration as exampled from gas pools from the Lower Cambrian in the Sichuan Basin. In this case, the oil was heated at a rate of 1 °C/Ma since the oil charge and experienced >200 °C for about 50 Ma. Thermochemical sulfate reduction may have enhanced the conversion of oil to gas, leading to an increase in EOGC values from 30% for non-TSR-altered oils to 98% for the strongly TSR-altered oil in the eastern Tazhong area with similar burial-heating history. A similar case for elevated EOGC due to TSR can be found in the Smackover Formation, Gulf of Mexico. Thus, two global models related to heating rate and duration at high temperatures and TSR are developed to illustrate oil stability with temperature and are expected to be instructive for deep petroleum exploration. • The extents of oil-gas conversion in the Tarim Basin vary widely in different areas. • Higher heating rates and shorter durations at high temperatures may favor the preservation of oil. • TSR could lower oil and gas stability and accelerate the conversion of oil to wet gas and of wet gas to dry gas. • Two global models are developed to illustrate oil stability with temperature. [ABSTRACT FROM AUTHOR]

It is hard to determine secondary microbial gas from deep burial reservoirs with multiple generations of petroleum charge. Herein, oils at depths from 5000 m to 6500 m in the Ordovician carbonate reservoirs, Tarim basin, are found to have been biodegraded to secondary microbial gas. These oils experienced severe biodegradation and thus contain abundant 25-norhopanes and 17-nortricyclic terpanes. The associated gases have methane δ13C 1 from −51.9‰ to −47.3‰ and δ2H 1 from −327.8‰ to −192.4‰, and CO 2 δ13C CO2 from −0.7‰ to +15.3‰. These features suggest that the gases are secondary microbial gas, generated predominantly via CO 2 reduction with preferential reduction of 13C-depleted CO 2 and contribution of methane hydrogen from formation water in closed environments. The secondary microbial gas may have generated from biodegradation of oils at reservoir temperatures of about <75°C during the Late Permian, and has subsequently mixed with a later charge of non-biodegraded oils and wet gas during the Late Cretaceous. Consequently, the present gas shows relatively low dryness (C 1 /∑C 1 – 4 < 0.87) and has varied δ13C 1 and δ2H 1 values in methane. The study implies that the signatures of secondary microbial gas can easily be masked by thermogenic gas and thus more secondary microbial gas has yet to be identified. [ABSTRACT FROM AUTHOR]

The strike-slip fault zones (SSFZs) of the central Tarim Basin have great potential for hydrocarbon exploration and development. They can both serve as hydrocarbon migration paths and host hydrocarbons. However, the complexity of SSFZ varies significantly along the fault strike, and strike-slip fault-controlled deeply buried carbonate reservoirs are often extremely heterogeneous, increasing exploration risks. Here, we reconstructed the architecture and setting of the SSFZ of the central Tarim Basin and analyzed the complex and heterogeneous hydrocarbon system that characterizes this exploration area. The integrated seismic and well datasets show that the development of SSFZs has led to the fracturing of tight carbonates and enhancements in the karstification process, secondary porosity and permeability due to the presence of open fractures. Based on the vertical height of the fault in the section and continuity, the SSFZs in the central Tarim Basin have been classified as 1st-order or 2nd-order faults. The 1st-order faults are found in the repeatedly reactivated vertical SSFZ, which is composed of sub-vertical strike-slip faults in the Paleozoic strata and en-echelon normal faults in the shallow layer. The 2nd-order faults develop only in Paleozoic strata without reactivated features. Continuous through-going, hard-linked 1st-order faults are a more valuable target for future exploration than soft-linked 2nd-order faults because 1st-order faults control larger-scale fracture-cavity reservoirs, and their fault activity periods correspond to hydrocarbon accumulation periods. We classified damage zones as wall-, and linking-damage zones, based on their location around the fault. There are two types of linking-damage zones, extensional steps and contractional steps, which develop in the extensional and contractional quadrants of the fault segment, respectively. Linking-damage zones are associated with more structural complexity than narrow and straight wall damage zones. Fractures in the contractional steps are generally closed and have low conductance, which is not suitable for fracture-cavity trap formation and hydrocarbon migration. Because opening-mode fracture development and permeability enhancement are greatest at the extensional steps, these locations are more likely to be important foci for strike-slip fault-controlled carbonate reservoirs. Our findings, in combination with previous research, indicate that fault zones in the central Tarim Basin, act as combined conduit-barrier systems, with damage zones typically featuring highly conductive fracture networks and fault cores acting as seals, resulting in heterogeneous reservoir distributions. • Different strike-slip faults in the central Tarim Basin have diverse geometric and kinematic characteristics. • The 1st-order strike-slip faults are the most favorable exploration targets. • The strike-slip faults exhibit complex linkages and interactions, leading to great heterogeneity in the fault-controlled reservoirs. [ABSTRACT FROM AUTHOR]

Abstract: The paleo-heat flow evolution of the Tabei Uplift in the Tarim Basin is investigated based on burial and thermal history reconstruction of 14 wells and using basin modeling. Numerous geological parameters, such as, temperature data and missing sediment thickness by erosion were used in the modeling. The basin model was calibrated using 460 measured vitrinite reflectance (%VR o) and vitrinite-like maceral reflectance (%VLMR o) values to constrain the validity of the maturity model. The heat flow history of the Tabei Uplift, Tarim Basin shows the following characteristics: (1) the highest paleo-heat flow was predicted to have occurred in the Early Ordovician as 65±5mW/m2, and gradually decreased to 55±5mW/m2 during the Late Carboniferous; (2) a thermal kick was modeled to have occurred in the Permian as suggested by an abrupt rise in the heat flow; (3) the heat flow gradually decreased since the Triassic; (4) the present day heat flow was predicted to be as low as 38mW/m2. This heat flow history honors the geologic and tectonic evolution history of the Tabei Uplift and is suggested as the best case heat flow model. [Copyright &y& Elsevier]

Newly discovered superdeep marine carbonate reservoirs with burial depths of more than 7000 m are found in the Shuntuo Low Uplift, Tarim Basin, China. Previous exploration experience indicates that strike-slip faults in these deposits played a key role in reservoir formation and hydrocarbon accumulation. This paper describes the structural and hydrocarbon characteristics of the SB5M strike-slip fault zone in the Shuntuo Low Uplift based on the study of high-quality 3-D seismic volumes and drilling data. The SB5M fault is a repeatedly reactivated strike-slip vertical fault zone. In the Paleozoic strata, the SB5M strike-slip fault zone is composed of sub-vertical strike-slip faults in the deep layer, a graben structure in the middle layer, and en-echelon normal faults in the shallow layer. The deep, middle and shallow faults developed sequentially at different times and formed as a result of three-stage evolution: the Middle Caledonian, Late Caledonian, and Middle-Late Hercynian. Fracture networks formed by repeated fault activity provided pathways for karst flow and hydrocarbons, which are conducive to the formation of fracture–cavity reservoirs. Due to the fault damage zone-fault core transition and the complex structural features, the reservoirs controlled by the SB5M strike-slip fault zone feature strong heterogeneity. The data sets presented and evolution models established in this paper provide important data for the exploration and development of the SB5M strike-slip fault zone and represent references for structural analysis and hydrocarbon exploration of strike-slip fault zones in the Tarim Basin and elsewhere. • Intracratonic strike-slip faults in Tarim Basin control the development of deep carbonate reservoirs. • The data sets in this paper provide important data for study a small-displacement intracratonic strike-slip fault. • This study represents a reference for structural analysis and hydrocarbon exploration of intracratonic strike-slip fault. [ABSTRACT FROM AUTHOR]