The Study On The Heterogeneity Of X2Reservoir Of Niujuanhu Area In Santanghu Basin

As to the Xishanyao reservoir of Niujuanhu area in Santanghu Basin, it is viewed as typically low porosity and permeability which has some matters with the reservoir development performance because of its serious heterogeneity of formation and fluid contained. Five kinds of the formation heterogeneity evaluation parameters have been favored according to the characteristics of petrography, diagenesis, microstructure, heterogeneity etal, which are studied via the SEM, cast thin section, high pressure Hg injection, true sandstone micro displacement and oil-water relative flow experiments. The comprehensive evaluation will provide some basis for enhancing both oil recovery and development effect.The main results and conclusions have been agreed as follows:1、The X2formation of Niujuanhu area can be subdivided into four intervals which are X21、X22、X23、X24from top to bottome2、In the study area Xishanyao formation is delta sedimentary system and mainly develops braided delta front subfacies which can be further subdivided into underwater distributary channel microfacies with most favorite quality in porosity, permeability and oil saturation; interdistributary microfacies; estuary dam with secondary reservoir quality.3、In virtue of intercalary strata mainly developed in X2formation, it has a relative strong in-layer heterogeneity with large discrepancy in permeability and positive rhythm and also has a strong horizontal heterogeneity about sand porosity and permeability4、Porosity mainly stems from residual intergranular pores, tuffaceous dissolved pores and feldspar dissolved pores, which is favorite type. So there are three types of pore combination:dissolution pore, dissolution-intercrystalline pore, intercrystalline-dissolution pore and micro pores.5、Sedimentary results in special divergence of reservoir petrography and quality. Compaction and cementation do harm to reservoir quality while dissolution improves a lot and also do fracture and fault caused by tectonic movement exacerbate macroscopic heterogeneity.6-. Concluded from waterflooding experiments, it is properties, microstructure heterogeneity, driving pressure and waterflooding times that mainly affect oil displacement efficiency.7> The reservoir heterogeneity has been divided by these evaluation parameters above into three classes:I, II, III. The formation X21、X22and X23are controlled by mainly type II and secondarily type I, few by type III. X24, mostly controlled by type I, is distributed widely.