Late Ordovician Reservoir Petrology and Characteristics of Reservoir Space in Tazhong Area,Tarim Basin

Combining field work with laboratory research,the reservoir petrology and pore characteristics of the Upper Ordovician Lianglitark Formation in Tazhong area have been studied in this paper.The results indicate that limestones in Lianglitark Formation in the study area are mainly framework reef limestone,grain limestone,argillaceous limestone,algae boundstone and karst breccia.Grain limestone mostly experienced multi periods of diagenetic transformation,in which fractures are relatively developed.The multistage pressure dissolution and dolomitization are common in micrite.The diagenetic transformation is the weakest in the algae boundstone.The types of pore space in the carbonate reservoirs are mainly large cavities,holes and cracks,of which holes most develop along the fracture and distributed sparsely and isolately,and crack is the main structural joints.Microscopic reservoir space mainly includes the dissolved pore and microfracture.Dissolution pores,which mainly develop in the grain limestone,can be subdivided into intragranular dissolved pore,intergranular dissolved pore,intercrystalline dissolved pore,moldic pore,dissolution skeleton hole,residual intergranular pore and dissolved microfracture pore,of which the intergranular dissolution pores have the highest proportion.Buried karstification is of large scale and widely distributed,which significantly influence the reservoir quality.