Formation characteristics and resource potential of Jurassic tight oil in Sichuan Basin

Abstract

Through test analysis of large amount of cores, rock fragments and crude oil samples, and in combination with dynamic data of production from 456 oil wells, hydrocarbon generation potentials of four major source rocks and accumulation characteristics of three major pay layers in the Jurassic of Sichun Basin were well investigated. Results indicated that source rocks in the Lianggaoshan Formation, the Da'anzhai Member and the Dongyuemiao Member mainly generated oil, and those in the Zhenzhuchong Member dominantly generated gas; the organic-rich source rocks controlled distribution of sweet spots of tight oil, and most industrial oil wells were located at the area with high-quality source rocks (TOC > 1.2%); and micron-sized pore throats were effective storage space, and fractures played a key role in initial high yield. Jurassic tight oil in the Sichuan Basin was characterized by light oil, high gas-oil ratio and abnormal high pressure, which were favorable for tight oil flow and output. Four methods (i.e., small bin method, resource abundance analogy method, EUR analogy method and total organic carbon method) were used to estimate Jurassic oil in-place in the Sichuan Basin which ranged from 2 × l09 to 3 × l09 t. Through analysis of main controlling factors of resource enrichment, the grading criteria were established for the evaluation of oil in-place in the Sichuan Basin. Through the small bin method, the oil in-place of Type I, Type II and Type III was 1.611 × l09 t, 0.477 × l09 t and 0.289 × l09 t, respectively. It was predicted that the largest exploration potential of the Da'anzhai Member was in the Nanchong-Suining area and the east of Liangping area, the most favorable exploration area of the Lianggaoshan Formation was in the Guang'an-Nanchong-Suining-Yilong area, and the good exploration prospect of the Dongyuemiao Member was in the south of the Guang'an-Suining area. Keywords: Tight oil, High-quality source rock, Preservation condition, Pore throat, Sweet spot, Resource evaluation, Jurassic, Sichuan Baisn