Postaccumulation sandstone porosity evolution by mechanical compaction and the effect on gas saturation: Case study of the Lower Shihezi Formation in the Bayan'aobao area, Ordos Basin, China

Xia, Lu; Liu, Zhen; Cao, Yingchang; Zhang, Wei; Liu, Junbang; Yu, Chunlan; Hou, Yingjie

doi:10.1016/j.marpetgeo.2020.104253

Cited by 8 publications

(3 citation statements)

References 49 publications

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“…After the compaction transformation, the intergranular porosity of the reservoir sandstone is significantly reduced. The porosity lost due to compaction is greater overall compared to that lost due to cementation (Xia et al, 2020).The porosity loss after compaction ranges between 16.0% and 27.9%, while the compaction rate falls between 40.0% and 69.8%, indicating a medium compaction diagenetic facies. The carbonate cement in the main area of Wenchang A oil field mainly consists of iron calcite, along with iron dolomite, siderite, glauconite, pyrite, and other minerals.…”

Section: Porosity and Permeabilitymentioning

confidence: 94%

Reservoir characteristics analysis and favorable area prediction of Zhuhai Formation, Wenchang A oilfield, South China Sea

Liu

2024

Front. Earth Sci.

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Wenchang A oilfield is a recently discovered low-permeability oilfield in the western South China Sea. The exploration target is the Zhuhai Formation, which reservoir lithology changes significantly, and the distribution of favorable reservoirs is unclear. In this study, the reservoir characteristics of the Zhuhai Formation in the Wenchang A oilfield, South China Sea, were analyzed through core identification, thin section identification, physical property testing, pre-stack geostatistical inversion, and frequency-based AVO inversion. Pre-stack geostatistical inversion is based on geostatistics and combines the seismic inversion algorithm with the stochastic sequential simulation algorithm. While the frequency-varying AVO inversion method is an extension of the conventional AVO inversion method, with its core technology being spectrum decomposition. After frequency division, multiple data sets directly participate in the calculation, which enhances the stability and accuracy of inversion.We also predict the favorable reservoir areas of six small layers in the Zhuhai Formation. The results show that 1) the reservoir lithology of the Zhuhai Formation mainly consists of feldspar quartz sandstone and feldspar quartz sandstone, indicating high compositional maturity. The porosity of the reservoir ranges from 14.0% to 19.0%, with an average value of 16.3%. The permeability of the reservoir ranges from 3.1 mD to 126.1 mD, with an average value of 22.4 mD, indicating a medium porosity and low permeability reservoir. The supporting structure of a sandstone reservoir is particle-supported, with the main contact being the “point-line” contact between particles. The main types of pores in sandstone are primary intergranular pores and secondary intergranular dissolved pores. Some pores are feldspar-dissolved pores, and occasionally there are hetero-based micropore. 2) The diagenesis of the Zhuhai Formation reservoir mainly includes compaction, cementation, and dissolution. Cementation and dissolution have minimal impact on the physical properties of reservoirs. The porosity loss of the reservoir after compaction ranges between 16.0% and 27.9%, and the compaction rate ranges between 40.0% and 69.8%, indicating a medium compaction diagenetic facies. 3) The favorable areas of each layer of the Zhuhai Formation are mainly concentrated in the southwest of the study area. The upper layer of ZH1I, the upper layer of ZH1II and the lower layer of ZH1II exhibit the best physical properties, the thickest favorable sand body, the strongest oil and gas display, the widest range of favorable areas, and the greatest exploration potential. The favorable exploration potential of layer 1 in the lower part of ZH1I and layer 2 in the upper part of ZH1II is moderate. The second layer in the lower part of ZH1II has the poorest properties and lower exploration potential. The main factors affecting the favorable area include physical properties, oil and gas display, sand body thickness, etc.

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Section: Porosity and Permeabilitymentioning

confidence: 94%

Reservoir characteristics analysis and favorable area prediction of Zhuhai Formation, Wenchang A oilfield, South China Sea

Liu

2024

Front. Earth Sci.

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“…The Ordos Basin continued to uplift as a result of the subduction of the paleo-Pacific Plate and Indian Plate since the Late Cretaceous [24]. It is widely accepted that the current underpressure and normal pressure in the Upper Paleozoic strata were the results of large-scale tectonic uplifting and denudation [16,55,61,62]. The temperature decrease, pore rebound, and natural gas dissipation during the uplifting stage were the main causes of the depressurization [55,63].…”

Section: Origin Of the Abnormal Pressurementioning

confidence: 99%

“…The stratum uplifting and denudation can lead to unloading of overburden pressure, which will increase the pore space and reduce the pore pressure [65]. Therefore, the depressurization resulting from pore rebound was closely related to the erosion thickness of the stratum [62,63]. The pore pressure in the sandstones decreased more intensively than that in the mudstones due to pore rebound, forming a pressure difference between source rock layers and reservoirs to promote gas expulsion and charging during the uplifting stage [61].…”

Section: Origin Of the Abnormal Pressurementioning

confidence: 99%

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Wang

Shi

et al. 2022

Energies

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The vague understanding of the coupling relationship among natural gas charging, reservoir densification, and pressure evolution restricted the tight gas exploration in the Lower Shihezi Formation of the Hangjinqi area, north Ordos Basin. In this study, the quantitative porosity evolution model, the pressure evolution process, and the natural gas charging history of tight sandstone reservoirs were constructed by integrated investigation of the reservoir property, the thin section, SEM and cathode luminescence observations, the fluid inclusion analysis and the 1D basin modeling. The results show that the compaction and cementation reduced the primary porosity by 21.79% and 12.41%, respectively. The densification of the reservoir occurred at circa 230 Ma, which was before the natural gas charging time from 192 to 132 Ma. The paleo-overpressure within the tight reservoirs occurred since the Middle Jurassic with the pressure coefficients between 1.1 and 1.55. The continuous uplifting since the Late Cretaceous resulted in the under- and normal-pressure of the Lower Shihezi Formation with the pressure coefficients ranging from 0.67 to 1.05. The results indicate that the densification of the reservoirs was conducive to the formation of paleo-pressure produced by gas generating. The gas predominantly migrated vertically, driven by gas expansion force rather than buoyance and displaced the pore water in the reservoirs near source rocks.

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Evolution of Permeability in Sandstone During Confined Brazilian Testing

et al. 2021

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Postaccumulation sandstone porosity evolution by mechanical compaction and the effect on gas saturation: Case study of the Lower Shihezi Formation in the Bayan'aobao area, Ordos Basin, China

Cited by 8 publications

References 49 publications

Reservoir characteristics analysis and favorable area prediction of Zhuhai Formation, Wenchang A oilfield, South China Sea

Reservoir characteristics analysis and favorable area prediction of Zhuhai Formation, Wenchang A oilfield, South China Sea

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Evolution of Permeability in Sandstone During Confined Brazilian Testing

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