Overpressure generation and evolution in a compressional tectonic setting, the southern margin of Junggar Basin, northwestern China

Locating and quantifying overpressures are essential to understand basin evolution and hydrocarbon migration in deep basins and thickly sedimented continental margins. Overpressures influence sediment cohesion and hence fault slip in seismically active areas or failure on steep slopes, and may drive catastrophic fluid expulsion. They also represent a significant drilling hazard. Here, we present a method to calculate the pore pressure due to disequilibrium compaction. Our method provides an estimate of the compaction factor, surface porosity and sedimentation rate of each layer in a sediment column using a decompaction model and the constraints imposed by seismic data and geological observations. For a range of surface porosities, an ad hoc iterative equation determines the compaction factor that gives a calculated layer thickness that matches the observed thickness within a tolerance. The surface porosity and compaction factor are then used to obtain a density profile and a corresponding estimate of P-wave velocity (V p ). The selected parameters are those that give a good match with both the observed and calculated layer thicknesses and V p profiles. We apply our method to the centre of the Eastern Black Sea Basin (EBSB), where overpressures have been linked to a lowvelocity zone (LVZ) at ca. 5500-8500 m depth. These overpressures were generated by the relatively high sedimentation rate of ca. 0.28 m ka À1 of the low permeability organic-rich Maikop formation at 33.9-20.5 Ma and an even higher sedimentation rate of ca. 0.85 m ka À1 at 13-11 Ma. We estimate a maximum pore pressure of ca. 138 MPa at ca. 8285 m depth, associated with a ratio of overpressure to vertical effective stress in hydrostatic conditions (kÃ) of ca. 0.7. These values are lower than those presented in a previous study for the same area.

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“…Hubbert & Rubey, , b; Bethke, ; Harrison & Summa, ). Tectonic compression (e.g. McPherson & Garven, ; Luo et al ., ).…”

Section: Introductionmentioning

confidence: 99%

A disequilibrium compaction model constrained by seismic data and application to overpressure generation in The Eastern Black Sea Basin

2012

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“…Particularly in cases where strong deformation caused coal mylonitization, the coal reservoir has extreme low permeability. Previous studies indicated that the folds in the SJB were formed by N-S compressional stress during the Himalaya Orogeny [32]. …”

Section: Geological Structure Controlsmentioning

confidence: 95%

“…Coal seams are up to a few meters thick, and parts of them are interbedded with sandstone and mudstone. The Badaowan Formation mainly developed in fluvial facies and swamp facies, while the Xishanyao Formation developed in delta facies, lacustrine facies, and swamp facies [32]. Total thickness of coal seams was remarkable, and Nos.…”

Section: Stratigraphic Characteristicsmentioning

confidence: 97%

Gas Content Evaluation of Coalbed Methane Reservoir in the Fukang Area of Southern Junggar Basin, Northwest China by Multiple Geophysical Logging Methods

Liu

Cai

et al. 2018

Energies

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Abstract:To study the gas potential of coalbed methane (CBM) in the Fukang area, southern Junggar Basin (SJB) of North China, different methods including multiple geophysical logging, the Kim method with proximate analysis data, and Langmuir adsorption were used to evaluate the gas content. Furthermore, the geological controls on gas content were evaluated. One hundred sixteen CBM wells with geophysical logging and 20 with field-measured gas content were adopted to assess the gas content in the Fukang area of SJB, NW China. The results show that the two geophysical logging variables (DEN and CNL) were favorable for evaluating the gas content due to the perfect correlation with the measured gas content. The gas content varies from 4.22 m 3 /t to 16.26 m 3 /t, and generally increases with increasing burial depth. The gas content in coal seams along the synclinal axis is significantly higher than that along the synclinal wing in the west zone. In the east zone, the gas content of the westward is higher than that of the eastward because of the fault coating effect by reverse fault. Generally, the gas content of the SJB is in the order of syncline > surrounding reverse fault > slope of syncline > slope of anticline > central of reverse fault, if only geological structure features are considered. The favorable areas for CBM concentration appear to be a composite gas controlling result of multiple geological factors. Two typical geological scenarios with low gas content and high gas content were revealed. In the Fukang area of SJB, the low gas content is mainly due to the normal fault and roof lithology of sandstone. The most favorable area of high gas content for CBM exploration and development is in the northeast, where reversed fault, synclinal axis, mudstone roof lithology, and burial depth coincide with high gas content.

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“…3). The mudstone compaction curves indicate variable degrees of compaction (Luo et al, 2007). The acoustic well-log analyses show that the relationship of travel time and depth in underpressured strata deviates from that in which compaction follows a normal trend with depth ( Fig.…”

Section: Distribution Of Present Underpressurementioning

confidence: 95%

Formation mechanism of underpressured reservoir in Huatugou oilfield of Qaidam basin

Tang

Zhang

et al. 2011

J. Earth Sci.

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Underpressured reservoirs are widespread in the Huatugou (花土沟) oilfield of the western uplift in Qaidam basin, western China. At depths between 462 and 1 248 m, the pressure of Neogene reservoirs in the Huatugou oilfield is only about 40% to 80% of hydrostatic pressure. Based on a study of the geological characteristics of these underpressured reservoirs, this work used fluid inclusion analysis and numerical simulation to investigate the mechanism creating these abnormal pressures and to evaluate the characteristics of the hydrocarbon distribution. The results show that the underpressured reservoirs are all well-sealed by undercompacted and thick mudrocks. The large-scale tectonic uplift in the late Himalayan plays an important role in the generation of underpressure in the Huatugou oilfield. At the beginning of this movement, the field was overpressured due to episodic petroleum accumulation. Later, structural uplift and erosion led to porous rebound and a temperature decrease, which produced the underpressure.

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Overpressure generation and evolution in a compressional tectonic setting, the southern margin of Junggar Basin, northwestern China

Cited by 63 publications

References 24 publications

A disequilibrium compaction model constrained by seismic data and application to overpressure generation in The Eastern Black Sea Basin

A disequilibrium compaction model constrained by seismic data and application to overpressure generation in The Eastern Black Sea Basin

Gas Content Evaluation of Coalbed Methane Reservoir in the Fukang Area of Southern Junggar Basin, Northwest China by Multiple Geophysical Logging Methods

Formation mechanism of underpressured reservoir in Huatugou oilfield of Qaidam basin

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