Shiyou shiyan dizhi (May 2021)
Study and application of identification and description methods for lithologic traps in large braided river sheet composite channels
Abstract
The gas reservoirs in the Permian tight sandstones in the Ordos Basin are characterized by near source, tightness, large-scale area of gas reservoir, distribution along the main channel, and strong heterogeneity. Influenced by the changes in the internal physical properties of sand bodies, the difference between gas and water is not obvious, and the gas boundary is also unclear. Therefore, the trap identification and the description of this type of gas reservoir is not like those for a single trap in the ubiquitous cases. It should be focused on the distribution of the composite channel sand bodies formed by the spatial superposition of effective single sand body, so as to determine the "sweet spots" of the maximum reserve unit. A case study was made for the first member of Xiashihezi Formation of Lower Permian in the Duguijiahan trap of Hangjinqi area, northern part of Ordos Basin. The characteristics as well as identification and description methods for lithologic traps in sheet-shaped composite channels of large-scale braided rivers were discussed. Constrained by the sequence framework and based on the geological model, a well-seismic joint analysis of sedimentary facies was employed here to realize the effective prediction and description of effective sandstone reservoirs and their boundary distributions in braided river channels. A six-step evaluation of this type of trap was introduced, which could predict the effective reservoirs in sheet-shaped composite channels of braided rivers by using relatively low-resolution seismic data. With the continuous application and improvement of the technical series, the proven natural gas reserves in lithological traps of the first member of Xiashihezi Formation in the Duguijiahan trap have exceeded 100 billion cubic meters.
Keywords
