Xianglu Tang

Geology and shale gas resource potentials in the Sichuan Basin, China

The organic-rich shales in the Sichuan Basin in China include Pre-Cambrian Sinian to Middle Permian marine shales deposited in passive margin to foreland settings, Upper Permian transitional shales deposited in a coastal swamp setting, and Triassic and Jurassic lacustrine shales deposited in a foreland setting. Regional shale property mapping, analysis of geochemistry, mineralogy and petrophysics based on sample tests, reservoir characterization of potential shale intervals, and recent exploration and production (E&P) results reveal that: Pre-Cambrian to Middle Permian marine shales, especially the Lower Silurian Longmaxi shale, deposited during transgressive systems tract to early highstand systems tract period have significant reservoir storage, high TOC, high maturity, high brittle mineral content and high gas content, and are similar to the Barnett shale in USA to hold a huge amount of shale gas. The coal-associated Upper Permian transitional shales and Triassic to Jurassic lacustrine shales are relatively clay-rich compared to marine shales, but possess some shale gas potential in organic-rich shales. The shale gas resource potentials and emerging production have been confirmed by the reservoir characteristics and test results of recent drilled wells targeting marine, transitional and lacustrine shale gas in the Sichuan Basin.

Characterization and origin of the Silurian Wufeng-Longmaxi Formation shale multiscale heterogeneity in southeastern Sichuan Basin, China

AbstractShale heterogeneity is important for micro- to macroscale-quality reservoir prediction. We evaluated the multiscale heterogeneity in shale based on thin-section observation, field emission scanning electron microscope observation, low-pressure N2 adsorption analysis, mercury intrusion porosimetry, organic carbon analysis, and bulk chemical analysis by X-ray powder diffraction. We evaluated the results in which the heterogeneity of minerals and organic matter in shale was shown by disorderly and unsystematically distributed mineral grains, lamina, and rapid lithology at multiple scales. The random arrangement of minerals, seasonal climate changes, large changes of sedimentary environment, and the provenance supply was considered to be the origin of the heterogeneity from the micro- to the macroscale in shale. In addition, a multiscale heterogeneity distribution model of marine shale in southeastern Sichuan basin was established, which can be used to predict shale gas distribution from the micro- to...

Effects of organic matter and mineral compositions on pore structures of shales: A comparative study of lacustrine shale in Ordos Basin and Marine Shale in Sichuan Basin, China:

The pore structure of shale plays key role in oil and gas storage capacity and accumulation. Twelve representative samples were selected from Triassic Yanchang Formation in the Ordos Basin and Silurian Longmaxi Formation in the Sichuan Basin with different ages, depositional settings, and maturities to analyze shale pore structure using focused ion beam-scanning electron microscopy and high-pressure mercury intrusion capillary porosimetry. The results show that the pores of lacustrine shale with maturity Ro < 1.3% from the Triassic Yanchang Formation were predominantly composed of pores with pore throat diameter of larger than 30 µm. The pores of marine shale with maturity Ro > 1.3% from the Silurian Longmaxi Formation were predominantly composed of pores with pore throat diameter of smaller than 100 nm. For the porosity, the average porosity of low-mature lacustrine shale is 2.4%, while the average porosity of high-mature marine shale is 1.5%. For the pore type, intergranular inorganic pores predominantly occurred between mineral particles in the lacustrine shale, while the marine shale mainly developed organic pores with pore throat diameters ranging from 5 to 200 nm. Compared to the low-mature lacustrine shale, macropores of high-mature marine shale are less developed and micropores dominant. Importantly, brittle minerals (quartz, feldspar, and carbonate minerals) mainly affect the pore structure of lacustrine shale, while organic matter mainly affects the pore structure of marine shale.

Factors controlling organic matter enrichment in the Lower Cambrian Niutitang Formation Shale on the eastern shelf margin of the Yangtze Block, China

AbstractThe degree of organic matter (OM) enrichment in shale determines its oil and gas potential. To understand the factors controlling this OM enrichment, we have used petrological and geochemical analyses to study the Lower Cambrian Niutitang Formation Shale in the eastern shelf margin of the Yangtze Block. Our results reveal that the total organic carbon (TOC) content of the Niutitang Formation Shale varies significantly throughout the vertical section. The lower part of the Niutitang Formation has a high TOC content, likely due to its formation in a dysoxic/anoxic environment with intense upwelling that favored OM enrichment. The middle part of the Niutitang Formation has the highest TOC content, which can be attributed to its formation in an environment with more hydrothermal activity, moderately upwelling, high paleosalinity, dysoxic/anoxic conditions, and moderately restricted water contents. Finally, the upper part of the Niutitang Formation records the lowest TOC contents because it likely form...

Characteristics and formation mechanisms of tight oil: A case study of the Huahai Depression, Jiuquan Basin, Northwest China

The exploration of tight oil reservoirs has achieved a big success, especially in the Huahai Depression, Jiuquan Basin, China, but the characteristics and formation mechanisms of the tight oil reservoir are unclear. In this paper, a series of analyses including thin section, scanning electron microscope, gas chromatography–mass spectrometry, isotope, and fluid inclusions were taken to study the tight reservoirs of the Xiagou Formation (K1g) and Zhonggou Formation (K1z) in the Huahai Depression. The results show that the main factors influencing the porosity and permeability of the tight reservoir are the compaction and two periods of carbonate cementation. The second type of carbonate cementation was related to the decarboxylation of organic acids in parts of the study area. The tight oil accumulation periods for different formations are confirmed, during 115–102 Ma in K1g1, 114–97 Ma in K1g2, and 103–85 Ma in K1z1, respectively. The tight oil migrations are executed for only several meters vertically but hundreds of meters even kilometers laterally. Two kinds of formation mechanisms exist in the study area. The main formation pattern is the “hydrocarbon accumulated after reservoir had tightened,” which has occurred in most of the study area. The other pattern, the “hydrocarbon accumulated during reservoir was tightening,” is found in several places of the study area.