Characteristics and controlling factors of tight sandstone reservoir fractures in the Xujiahe Formation of the western Yuanba area, northeastern Sichuan Basin

Abstract

The Xujiahe Formation in the western Yuanba area of the northeastern Sichuan Basin was slightly affected by late tectonic activity and thus has fewer fractures relative to the central and eastern Yuanba areas. Utilizing core observation, slice identification, logging interpretation, and inclusion analysis, the characteristics and controlling factors of fractures in tight sandstone of the Xujiahe Formation of the western Yuanba area were analyzed.The results show that the study area mainly contains low-angle shear fractures and diagenetic fractures. Fractures in the 2nd and 3rd members of the Xujiahe Formation were primarily filled by calcite and clay respectively. The fractures in the Xujiahe Formation of the study area can be classified into three stages, corresponding to the regional tectonic deformations during the Late Jurassic, the end of the Early Cretaceous, and the Late Himalayan. The fractures of the 1st and 2nd stages were fully or partly filled, but the 3rd stage fracture was not filled. The development of fractures was mainly affected by the fault and fold deformation strength, lithology combination, and stratum thickness. Fractures in the hinge zone and southeast limb of Jiulongshan anticline were mainly generated by bending deformation except for the fault zone. The fault-related fracture was more plentiful in the vicinity of the fault zone. Both bending deformation fracture and fault-related fracture are favorable for petroleum development. Fractures in the conglomerate of 3rd Member of the Xujiahe Formation can terminate at or transect the gravel particle and generally show small apertures. The low-angle fractures and micro-fractures in the quartz sandstones of the 2nd Member of the Xujiahe Formation developed aligning with bedding. Both the 3rd and 2nd members of the Xujiahe Formation in the study area are favorable targets for petroleum exploration and development.

Keywords

• northeastern sichuan basin
• western yuanba area
• xujiahe formation
• tight sandstone
• fracture characteristics