Diagenesis of the coal-rich fluvial sediments and reservoirs in the Xishanyao Formation,Turpan depression,Xinjiang

A series of coal-bearing continental strata was laid down within the Xishanyao Forma-tion,Turpan depression,Xinjiang.These strata are interpreted in this paper as the mean-dering river deposits in accordance with well logs,which in turn may be subdivided into channel bar and backswamp deposits.The coal seams commonly occur in the backswamp environment.The meandering channel sandbodies appear as the substantial reservcir sand-stones.For instance,the channel sandstone complexes occupy the meander belts in the southeastern part of the depression,where the reservoir sandstones are well developed. The reservoir sandstones consist mostly of lithic sandstones and feldspathic litharenite with lower mineral maturity.The channel sandstone complexes are dominated by felds-pathic litharenite in the southeastern part of the depresison,where the dissolution is be-lieved to be the typical diagenesis resulting in the formation of pore spaces with solution pores of sandstones.The channel sandstones comprise the bulk of lithic sandstones in the northern part of the depression,where compaction is considered as the typical diagenesis giving rise to the poor physical properties of the reservoir sandstones.The diagenesis of the reservois in the Xishanyao Formation are mainly manifested in compaction,cementation and dissolution.