Unconventional reservoirs are keys to oil and gas exploration and development, especially shale gas reservoirs.
Discriminated shale gas reservoir lithofacies are, in particular, a primary problem in shale gas reservoir engineering. The
mineral composition will affect both absorbed and free gas contents, therefore their identification is important. The mineral
composition is one part of lithofacies. The shale content has always been used in previous lithological identifications:
this method is effective in sand reservoirs; however, it is not suitable for use in shale gas reservoirs. This paper takes No.7
section in Yanchang formation in Ordos basin as an example. Through a lithological analysis, it was concluded that overlap
method and cross-plot method are not also inappropriate for shale gas reservoirs. The Ordos basin shale gas reservoir
is divided into seven lithofacies. We form a mathematical method and apply it to shale gas reservoirs using the shale volume
and ΔlgR which are available from conventional well logging and reflect organic matter in the processed dataset. Decision
tree is used here. However, there were too many parameters to discriminate all lithofacies precisely. Principal component
analysis (PCA) is a technique used to reduce multidimensional data sets to lower dimensions for analysis. This
technique can be useful in petro-physics and geology as a preliminary method of combining multiple logs into a single entity
or two logs without losing information. Combining PCA and a decision tree algorithm, the lithofacies of a shale gas
reservoir were accurately discriminated.
The Heterogeneity of Lacustrine Shale Gas Reservoir in Yanchang Formation, Xiasiwan Area, Ordos Basin
