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Tight Gas Sandstones (tight + gas_sandstone)
Selected AbstractsTectonic Fractures in Tight Gas Sandstones of the Upper Triassic Xujiahe Formation in the Western Sichuan Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010ZENG Lianbo Abstract: The western Sichuan Basin, which is located at the front of the Longmen Mountains in the west of Sichuan Province, China, is a foreland basin formed in the Late Triassic. The Upper Triassic Xujiahe Formation is a tight gas sandstone reservoir with low porosity and ultra-low permeability, whose gas accumulation and production are controlled by well-developed fracture zones. There are mainly three types of fractures developed in the Upper Triassic tight gas sandstones, namely tectonic fractures, diagenetic fractures and overpressure-related fractures, of which high-angle tectonic fractures are the most important. The tectonic fractures can be classified into four sets, i.e., N-S-, NE-, E-W- and NW-striking fractures. In addition, there are a number of approximately horizontal shear fractures in some of the medium-grained sandstones and grit stones nearby the thrusts or slip layers. Tectonic fractures were mainly formed at the end of the Triassic, the end of the Cretaceous and the end of the Neogene-Early Pleistocene. The development degree of tectonic fractures was controlled by lithology, thickness, structure, stress and fluid pressure. Overpressure makes not only the rock shear strength decrease, but also the stress state change from compression to tension. Thus, tensional fractures can be formed in fold-thrust belts. Tectonic fractures are mainly developed along the NE- and N-S-striking structural belts, and are the important storage space and the principal flow channels in the tight gas sandstone. The porosity of fractures here is 28.4% of the gross reservoir porosity, and the permeability of fractures being two or three grades higher than that of the matrix pores. Four sets of high-angle tectonic fractures and horizontal shear fractures formed a good network system and controlled the distribution and production of gas in the tight sandstones. [source] OBTAINING FRACTURE INFORMATION FOR LOW-PERMEABILITY (TIGHT) GAS SANDSTONES FROM SIDEWALL CORESJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2006S. E. Laubach We illustrate a fracture characterization technique applicable to all tight gas sandstones. The technique uses microfractures and cements in the rock mass identified using SEM-based cathodoluminescence imaging to provide information on unsampled large fractures, including strike and cross-cutting relationships, intensity, and likelihood of preserved open fractures. We applied the technique in two tight gas sandstone wells in the Pennsylvanian Pottsville Formation, Black Warrior Basin, Alabama, USA. In one well, data was obtained entirely from drilled 1,inch diameter sidewall cores that were oriented using image logs and features visible in cores. We predicted fracture porosity preservation in large fractures using late cements in the rock mass as a proxy for fracture observation. Results from the technique are consistent with what is known of large fractures in this area. Where we predicted open, high intensity fractures, substantial gas flares were observed during drilling. By combining microstructural and diagenetic observations, it is possible to overcome the inadequate fracture sampling that plagues evaluation of natural fractures and that relies solely on observations of macroscopically visible fractures. [source] Tectonic Fractures in Tight Gas Sandstones of the Upper Triassic Xujiahe Formation in the Western Sichuan Basin, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2010ZENG Lianbo Abstract: The western Sichuan Basin, which is located at the front of the Longmen Mountains in the west of Sichuan Province, China, is a foreland basin formed in the Late Triassic. The Upper Triassic Xujiahe Formation is a tight gas sandstone reservoir with low porosity and ultra-low permeability, whose gas accumulation and production are controlled by well-developed fracture zones. There are mainly three types of fractures developed in the Upper Triassic tight gas sandstones, namely tectonic fractures, diagenetic fractures and overpressure-related fractures, of which high-angle tectonic fractures are the most important. The tectonic fractures can be classified into four sets, i.e., N-S-, NE-, E-W- and NW-striking fractures. In addition, there are a number of approximately horizontal shear fractures in some of the medium-grained sandstones and grit stones nearby the thrusts or slip layers. Tectonic fractures were mainly formed at the end of the Triassic, the end of the Cretaceous and the end of the Neogene-Early Pleistocene. The development degree of tectonic fractures was controlled by lithology, thickness, structure, stress and fluid pressure. Overpressure makes not only the rock shear strength decrease, but also the stress state change from compression to tension. Thus, tensional fractures can be formed in fold-thrust belts. Tectonic fractures are mainly developed along the NE- and N-S-striking structural belts, and are the important storage space and the principal flow channels in the tight gas sandstone. The porosity of fractures here is 28.4% of the gross reservoir porosity, and the permeability of fractures being two or three grades higher than that of the matrix pores. Four sets of high-angle tectonic fractures and horizontal shear fractures formed a good network system and controlled the distribution and production of gas in the tight sandstones. [source] | ||||||||||