Characteristics of overpressure distribution and its implication for hydrocarbon exploration in the Qiongdongnan Basin

Shi, Wanzhong; Xie, Yuyuan; Wang, Zhenfeng; Liu, Xusheng; Tong, Chuanxin

doi:10.1016/j.jseaes.2012.12.037

Cited by 54 publications

(41 citation statements)

References 19 publications

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“…The comprehensive stratigraphic column of the Qiongdongnan Basin (modified from Shi et al, ) [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Geologic Settingmentioning

confidence: 99%

“…Very thick and large‐scale sedimentary units were deposited in the central and southern depression belts in the Palaeogene and Miocene formations, which resulted in overpressure in the deep basin. The pressure in the whole basin increased gradually from south to north, and the pressure in the central sags rose as the depth increased (Shi, Xie, Wang, Li, & Tong, ; Wang et al, ; Zhai & Chen, ). As a consequence, the rapidly deposited, undercompacted thick shale provided the foundation for the formation of mud diapirs and gas chimneys in the QDNB (Hu et al, ; Zhang, Liang, Yang, et al, ; Zhao et al, ).…”

Section: Geologic Settingmentioning

confidence: 99%

“…In addition, the average geothermal gradient of the QDNB is high (approximately 4°C/100 m; Yuan et al, ), and the geothermal gradient in the central and southern depression belts is higher than the mean value of the QDNB (Tang et al, ), which is close to the geothermal gradient in the central mud diapiric structure zone of the YGHB (Lei, Ren, Clift, et al, ; Liu et al, ). Obviously, the combined high geothermal field and the abnormally high pressure potential in the rapidly deposited, undercompacted shale created the favourable conditions and driving forces for the generation and evolution of mud diapirs and gas chimneys (Shi et al, ; Wang, Liu, et al, ; Yang et al, ; Zhai & Chen, ; Zhang, Liang, Yang, et al, ). Furthermore, the hydrocarbon‐generating pressurization of the Palaeogene source rocks also formed the perfect conditions for the diapiric activities that served as an important supplement of high temperature and overpressure potential (Kong, ).…”

Section: Geologic Settingmentioning

confidence: 99%

“…The location (a) and structural units (b) of the Qiongdongnan Basin in the northern South China Sea (modified from Huang et al, ; Shi et al, ). The gas field locations are from Huang et al (), Zhang et al (), and Zhang, Xu, et al ().…”

Section: Introductionmentioning

confidence: 99%

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Distribution and characteristics of mud diapirs, gas chimneys, and bottom simulating reflectors associated with hydrocarbon migration and gas hydrate accumulation in the Qiongdongnan Basin, northern slope of the South China Sea

Zhang

Gong

et al. 2018

Geological Journal

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A comprehensive analysis on high‐resolution seismic data and the geological characteristics of the Qiongdongnan Basin (QDNB) in the northern South China Sea reveals multiple seismic evidence indicative of hydrocarbon migration and gas hydrate accumulation, including mud diapirs, gas chimneys, bottom simulating reflectors (BSRs), acoustic blanking, enhanced reflections, V‐AMP structures, elevated stacking velocity of sediments, and seafloor expressions. Mud diapirs and gas chimneys, which are characterized by acoustic turbidity, fuzziness, and blanking reflections on seismic profiles, with a diversity of structures and scales, are widespread and concentrated in the centres of sags and the transitional zones between sags and uplifts. Five BSR regions, with a total area of approximately 11,000 km2, have been delineated in the QDNB. They have high or medium‐high continuity amplitudes with overlying acoustic blanking on seismic profiles, indicating the occurrence of gas hydrate. Distinct fluid seepage phenomena are common below the BSRs, demonstrating that abundant free gas has migrated and accumulated beneath the gas hydrate. The distribution of BSRs and the developed zones of mud diapirs and gas chimneys presents a spatial superposition feature, and the BSRs are usually located on top of or within the structural highs of the mud diapirs and gas chimneys, indicating a close relationship between them. Mud diapirs, gas chimneys, and associated faults are efficient pathways for migrating hydrocarbons, through which the mature to highly mature thermogenic gas of the Palaeogene strata and the biogenic gas of the Neogene sediments migrate to the gas hydrate stability zones and form gas hydrate. Gas hydrate samples were recovered from the gas chimney area during the remote operated vehicle (ROV) investigation in deepwater QDNB in 2015. Based on the seismic interpretation and geochemical results, we propose two models of gas hydrate accumulation in the deepwater area of the QDNB: (a) near source biogenic gas hydrate with self‐generation and self‐accumulation, and (b) distal source thermogenic gas hydrate with lower generation and upper accumulation. We believe that the areas with a fine spatial coupling configuration between the mud diapirs, gas chimneys, and BSRs are favourable exploration targets for gas hydrate in the QDNB.

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“…The comprehensive stratigraphic column of the Qiongdongnan Basin (modified from Shi et al, ) [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Geologic Settingmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Distribution and characteristics of mud diapirs, gas chimneys, and bottom simulating reflectors associated with hydrocarbon migration and gas hydrate accumulation in the Qiongdongnan Basin, northern slope of the South China Sea

Zhang

Gong

et al. 2018

Geological Journal

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“…The overpressure existing in the Raghavapuram or Vadaparru Shale formation can drive hydrocarbon migration from the source rock to the traps (Tang and Lerche 1993;Hao et al 2002). Enhanced overpressure (pressure coefficient greater than 1.8) can also crack the formation and push the sandstone intrusion into the shale, and responsible for the formation of the sand injectites that create new areas for hydrocarbon exploration and production (Shi et al 2013;Hurst et al 2011).…”

Section: Relationship Between Pore Pressure Fracture Gradient and Inmentioning

confidence: 99%

Overpressure Zones in Relation to In Situ Stress for the Krishna-Godavari Basin, Eastern Continental Margin of India: Implications for Hydrocarbon Prospectivity

Chatterjee

Paul²,

Singha

et al. 2015

Springer Geology

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An analysis for over pressure zone (OPZ) prevailing in parts of the Krishna-Godavari Basin (KG-B) at the Eastern Continental Margin of India (ECMI) is found promising from the viewpoint of its hydrocarbon potentials. Pressure coefficients estimated from pore pressure studies reveal that there is a rather extensive (lateral) OPZ in the study area than hitherto expected with maximum pressure coefficient of 1.31 or more. The stress magnitudes like vertical stress (S v ), minimum horizontal stress (S h ) and pore pressure gradient (PPG) and fracture pressure gradient (FPG) are predicted from well log data for 15 available wells distributed over an area of 6022 km 2 in KG-B. The wells are drilled to depths of 3660 m on-land (#Wells 1-9) and up to 4000 m in offshore (#Wells 10-15). The PPG ranges from 11.85 to 13.10 MPa/km, whereas, the FPG varies from 17.40 to 19.78 MPa/km in sediments penetrated by the wells displaying normal pressured sediment to a significantly higher value of 19.78 MPa/km for the over-pressured sediments. The values of vertical stress gradient (VSG) varies from 14.67 to 23.10 MPa/km, whereas, the values of S h magnitude varies from 64 to 77 % of the S v in normally-pressured to over-pressured sediments. VSG, PPG and FPG tend to decrease with corresponding increase in water column for the studied offshore wells. These results are utilized for constructing contour maps for observing the variations in the VSG and in the OPZ-top, also for constructing PPG contour map in 3D along the vertical section connecting all 15 wells extending from onshore to offshore regions. Any significant increase in pore pressure means the decrease of effective horizontal stress in respect of depth. As a result, the safety windows or safe mud-weight windows (the difference between PPG and FPG corresponding to particular depth interval in a well) will also decrease with the increase of PPG and FPG. Analytical approach adopted above is then critically examined to recommend how a priori steps based on petrophysical characters of a formation are closely monitored in time and optimum mud weight maintained during drilling.

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Detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the Krishna-Godavari Basin, India

Singha

Chatterjee

2014

Geochem. Geophys. Geosyst.

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Abnormally high pressures, measured by repeat formation tester (RFT) and detected by well log data from 10 wells in the Krishna-Godavari (K-G) Basin, occur in the Vadaparru Shale of Miocene and Raghavapuram Shale of Early Cretaceous age. Overpressures generated by disequilibrium compaction, and pore pressures have been estimated using the conventional Eaton sonic equation with an exponent of 3.0. The observed abnormal pore pressure gradient ranges from 11.85 to 13.10 MPa/km, whereas fracture pressure gradient varies from 17.40 to 19.78 MPa/km. The magnitude of vertical stress (S v ) has a gradient from 21.00 to 23.10 MPa/km. The minimum horizontal principal stress (S h ) magnitude is found to vary from 64 to 77% of the S v in normally pressured to overpressured sediments. A multiple linear regression model with a squared multiple correlation coefficient (R 2 ) of 0.94 is proposed for pore pressure prediction from gamma ray, density and sonic logs to focus on efficient drilling operations and to prevent borehole instability. The statistical model has been calibrated with the RFT data from five wells covering about 3400 sq. km area of the onshore K-G Basin. The model predicted pore pressure values are in close agreement with the actual RFT data for another four wells including a well in the offshore K-G Basin. Hence, the proposed regression model may be useful for predicting pore pressure from other well logs in the K-G Basin.

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Characteristics of overpressure distribution and its implication for hydrocarbon exploration in the Qiongdongnan Basin

Cited by 54 publications

References 19 publications

Distribution and characteristics of mud diapirs, gas chimneys, and bottom simulating reflectors associated with hydrocarbon migration and gas hydrate accumulation in the Qiongdongnan Basin, northern slope of the South China Sea

Distribution and characteristics of mud diapirs, gas chimneys, and bottom simulating reflectors associated with hydrocarbon migration and gas hydrate accumulation in the Qiongdongnan Basin, northern slope of the South China Sea

Overpressure Zones in Relation to In Situ Stress for the Krishna-Godavari Basin, Eastern Continental Margin of India: Implications for Hydrocarbon Prospectivity

Detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the Krishna-Godavari Basin, India

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