Logging Evaluation Of The Upper Member,Upper Ganchaigou Formation,Zhahaquan Area

Recently, the low porosity and low permeability reservoir distributed in Zhahaquan area of Qaidam Basin has been discovered in Neogene Shangganchaigou Formation. Though the research of the low porosity and low permeability reservoir has a certain theoretical basis, there still exsists plentiful difficulties and deficiencies when referred to the well logging evaluation, including complex pore structures, increased formation water salinity, coexsistence of low resistivity reservoir and high resistivity water stratum as examples of complex logging response characteristics, it is really a hard work to identify favorable reservoir and interpret oil-bearing identification.To address the above issues, four-properties relations are focused and mainly studied according to comprehensive analysis of basic geological data, logging data, analytical experiment as well as test and production information, plus the comprehensive use of using overlapping diagram, cross-plot method, and oil saturation logging quantitative interpretation to make well logging evaluations of shangganchaigou formation of the research area. The specific and principal understandings are listed as follow:(1) The ??? sand members of upper shangganchaigou formation in zhahaquan area are typical low porosity and low permeability reservoir. Reservoir rock types are mainly fine sandstone and siltstone, the clay minerals are dominated by illite, residual intergranular pore is the main pore types with a few cracks of the reservoir.(2) Based on "core scale logging", HSGR overlap can rapidly qualitatively identify lithology attributed to the four-propertied relations combined with CNL, multiple linear regression is performed by using acoustic time difference, compensated density, compensated neutron and gamma ray relative value. Predicted porosity accuracy is relative higher, therefore the oil stratum, water layer and dry layer can be identify effectively by using the AC-RL overlap.(3)Through reservoir characteristics'analysis of ??? sand members of shangganchai formation, pelitic sandstone water saturation formula with mercury injection curve which verified by computation of "J" function Method all demonstrate that this method gets high accurate calculation results.