Reservoir Evaluation And Model Building-case Study Of Chang 6 Reservoir Of ZhongShanchuan Oil Region In Wa YaoBao Oilfield In Northern Shaanxi

Wayaobao oilfield located in the middle part of Shaanbei slope in Ordos Basin.Its main oil-bearing horizon were Chang 2 reservoir,chang 4+5 reservoir, and chang 6 reservior which are extra-ultra low permeability detrital reservior with flat structure, in the Triassic Yanchang formation. At present, the reservoirs are in the early development stage.In this paper, made Chang 6 reservoir as the major study-target of the main oil-bearing series in the WaYaoBao oilfield. Comprehensively with utilization of drilling, logging and various analytical data, applying the modern theories and techniques of reservoir evaluation, the sedimentary microfacies, reservoir petrology and diagenesis, pore structure and physical properties characteristics of the Chang 6 reservoir were studied and reservoir heterogeneity and sensitivity have been made.The study shows that, Chang 6 reservior of wayaobao oilfield which located in the front facies belt of Ansai-Zichang delta can be divided into four sedimentary microfacies,which are inter-distributary channel, distributary depression , subaqueous distributary channel, and diversion among bay. The inter-distributary channel and Subaqueous distributary channel are the most favorable sedimentary facies.The type of the reservoir rock was from gray-brown to gray debris-feldspar sandstone and feldspar sandstone. Compaction,pressure solution and cementation were main types of diagenesis. Dissolution pore was the mainly saving type of reservoir and residual intergranular pore followed. Dissolution pore - intergranular pore was the main porous compositioni.The average value of the porosity and penetration rate of the reservoir were separately 10.7% and 1.2×10-3μm2. So Chang 6 reservoir was a low porosity and low permeability reservoir.The heterogeneity of the reservoir showed as extremely unbalanced nature of the oil and gas distribution performance in the vertical and plane.The sensitivity of the reservoir was characterized by contradictions on the stress sensitivity, acid sensitivity damage, alkali sensitivity and speed sensitivity as a secondary contradictions. Combined with conventional middle and high permeable reservoir evaluation method , made permeability ,ratios of pore volume to particle volume ,flowing zone index, pore-throat radius ,uniformity coefficient and threshold pressure as ultra-low permeability reservoir evaluation index system and the application of fuzzy mathematics to establish extra-ultra-low permeability reservoir evaluation index system and programs,the comprehensive evaluation of Chang 6 reservoir has been evaluated .The result of the comprehensive evaluation showed that Chang 6 reservoir in research area can be divided into 4 types and mainly belongs to theⅡchass reservoir, next was theⅠchass reservoir .Sandbody skeleton model, structural model, facies model and attribute model have been established through the applications of petrel modeling software and the adaptation of sequential indicator Simulation, which will provid foundation for the efficient development for the oilfield.