Development characteristics and prediction of fractures in deep-ultradeep tight sandstone reservoirs of Kuqa Depression: a case study of the Bashijiqike and Baxigai formations in Dabei 9 Block

Deep-ultradeep tight sandstone gas reservoirs are extremely important promising future energy. Natural fractures can improve the permeability and impact the overall reservoir quality. With the Dabei 9 Block of Kuqa Depression as an example, this study investigated and predicted the development and distribution of natural fractures in the tight sandstone reservoir based on R/S analysis method. Tensile-shear fractures are dominant fracture type within the block. Natural fractures primarily strike NW-SE and NE-SW directions with relatively high dip angle. Nearly 50% fractures are unfilled and partly filled. The coefficient index of fracture development Q was defined and calculated according to the lg(R/S) function. Error analysis of fracture prediction was also carried out. The results show that the Q corresponds to fracture density, and higher Q value commonly indicates larger density. Errors between fracture predictions and measures can be caused by various factors including fracture occurrence, fracture filling, limitation of conventional logging range, and multiple interpretations of logging curves. This study is expected to provide geological references for tight sandstone gas exploration and development in the Dabei 9 Block of Kuqa Depression.