Permian carbonate reservoirs from the Qiangzi-5 well in the Qiangtang Basin, northern Xizang: Characteristics and influencing factors

The Qiangzi-5 well drilled into the Permian Longge and Zhanjin Formations is located in the Qiangtang Basin, northern Xizang. Lithologically, the carbonate rocks as the reservoir rocks are dominantly made up of micritic limestones, grainstones, bioclastic limestones, brecciola and silty or fine-grained dolostones. The pores as main reservoir spaces contain intergranular pores, intergranular solution openings, intragranular solution openings, intercrystal pores and intercrystal solution openings and other solution openings generated along the stylolites. The fissures are assembled by the structural fissures, pressure solution fissures and dissolved fissures. The porosities vary between 0.3% and 2.3%, with an average of 1.31%. The permeabilities range from 0.0034×10^-3 μm² to 0.0062×10^-3 μm², with an average of 0.0044×10^-3 μm². The diagenesis and tectonism are believed to be the main influencing factors for the porosities and permeabilities of the carbonate reservoirs. The constructive diagenesis encompasses the pressure solution, dissolution, dolomitization and tectonism while the destructive diagenesis includes compaction, cementation, recrystallization and silicification.