The characteristics of the tight gas reservoir with strong heterogeneity and its 3D recovery technology in Yan’an gas field, China

Abstract

The Yan’an gas field is located in the southeastern part of the Ordos Basin of China. After years of research, we have clarified the characteristics of the upper Paleozoic tight sandstone reservoirs: four main sets of intervals, including the Carboniferous Benxi Formation, the Shan second and Shan first members of the Permian Shanxi Formation, and the He eighth member of the Permian Lower Shihezi Formation, are multilayer complex superposed tight sandstone reservoirs that developed under the control of multiple differential sedimentary systems. Compared with the northern gas field, the upper Paleozoic reservoir is characterized by the small-scale effective sand body and poor physical property in the Yan’an gas field; the heterogeneity of the upper Paleozoic tight reservoir varies greatly: the heterogeneity of the He eighth and the Shan first members was increasing from the north to the south of the research area, owing to the intersection of the north and south provenance. The Shan second member indicates an obviously opposite trend: the heterogeneity of the Benxi Formation weakened from the center to both sides; the Yan’an gas field developed four main superposed composite sand bodies types, including the vertical superposed, lateral migration, cut superposed, and isolated types. Due to the existence of the interlayers rich in mudstone and soft debris near the architectural boundary, the reservoir sand body has strong structural heterogeneity under the interaction of differential diagenesis and densification. Aiming at the strong heterogeneity and multilayer complex superposition characteristics of the Yan’an gas field, we have made clear the constraints and matching relationships between control factors and well-pattern elements on the basis of deep analysis. We have formed the hybrid well pattern for 3D recovery technology that unlocked multilayer complex superposed tight sandstone gas reservoirs with strong heterogeneity in the southeastern portion of the Ordos Basin.