Characteristics and types analysis of gas reservoir in Shan 2 section of Yan'an gasfield, Ordos Basin

Yan'an gasfield in the southwest of Yishan slope was studied. The results show that the reservoir of section 2 of Shanxi Formation exhibits several characteristics. The reservoir distribution is not stable in plane, and the spatial configurations between sand-bodies, or between sand-body and surrounding rock are various. The reservoir is tight, whose porosity mainly ranges from 1.0% to 10.0% and permeability mainly ranges from 0.01×10-3 μm2 to 0.4×10-3 μm2. Stratification and inner heterogeneity are serious. Differentiation of gas and water is not obvious and the reservoir is lacking in a uniform gas-water interface. There is a certain diversity of gas properties among sand-bodies. Methods of distribution direction of sand, orientation and well spacing, logging facies comparison are used to determine the connectivity of sand-bodies between wells. Some sand-bodies are connected, however, the corresponding measured gasfield pressure, gas saturation and component are different, which means the reservoir forming system is generally not the same. According to reservoir forming mechanism analysis, research concludes that inhomogeneity of hydrocarbon accumulation factors which experienced several stages in section 2 of Yan'an gasfield Shanxi formation, and lead to the gas-water distribution inhomogeneity is produced, inherited and retained. This mechanism and process form a seeming "connectivity" in space domain, but actually the reservoir forming system is "non- uniform". The gas reservoir layer possesses three characteristics: inhomogeneity tight reservoir, quasi-connectivity trap distribution, non-uniform reservoir system. Thus, the reservoir type can be defined as a "quasi-consecutive tight gas sandstone reservoir". © 2016, Central South University of Technology. All right reserved.