Source Rock Characteristics and Hydrocarbon Expulsion Potential of Lower Permian Fengcheng Formation in Fengcheng Area, Junggar Basin, Northwest China: Implications for Tight Oil Potential

Abstract

Tight oil refers to oil resources accumulated in tight sandstone or tight carbonate reservoirs that are interbedded with, or close to, source rocks. Significant progress has recently been made in tight oil exploration of the Fengcheng (P1f) Formation in the Fengcheng area (FA) at the northwest margin of the Junggar Basin, northwest China. Source rock is one of the factors responsible for the formation of tight oil resources, and studies of the original hydrocarbon generation potential and hydrocarbon expulsion efficiency of source rocks are of great significance for assessing tight oil potential. Several studies have been conducted on the P1f source rocks, but there is still a lack of knowledge of the hydrocarbon generation and expulsion characteristics of these rocks, thereby resulting in a failure to accurately assess the tight oil accumulation potential. Based on comprehensive analyses of geological and geochemical characteristics of well data, seismic inversion, sedimentary facies, tectonic burial depth, characteristics of the P1f source rocks (including distribution, sedimentary environment, organic matter content, organic matter type, and thermal maturity) are investigated. Results indicate that the P1f source rocks occur widely (area up to 2039 km2), are thick (up to 260 m), were deposited in a lacustrine weakly reducing sedimentary environment with relatively low salinity, have a highly variable total organic content (TOC, ranging from 0.15 to 4 wt %), are dominated by type II kerogen, and have reached the early mature to mature stage. The hydrocarbon generation potential methodology, together with basin simulation techniques, was applied to elucidate hydrocarbon generation and expulsion characteristics of the P1f source rocks in the FA. Modeling results indicate that the source rocks reached a hydrocarbon generation threshold and expulsion threshold at 0.5 % vitrinite reflectance (VR) and 0.85 % VR, respectively, with a comprehensive hydrocarbon expulsion efficiency of approximately 46 %; and an amount of 3.19 × 109 t and 1.53 × 109 t of hydrocarbons generated and expelled, respectively, from the P1f source rocks. The tight oil resource (in-place resource) of the P1f tight reservoir is approximately 0.61 × 109 t, indicating that the P1f Formation of the FA, Junggar Basin, has significant tight oil potential. Key words: Tight oil potential; Hydrocarbon expulsion characteristics; Source rock characteristics; Fengcheng Formation; Junggar Basin; China

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017