Shale Oil Geological Characteristics and Resource Potential of Mesozoic Yanchang Formation in Ordos Basin, North-Central China

Abstract

Shale oil in this paper is referred to as the matured oil, which is stored in organic-rich shale stratum with nano-sized pore-throats, and is a very promising exploration field in future. Taking shale oil of Mesozoic Yanchang Formation in Ordos Basin for example. Shale oil occurs in the organic-rich shale in the middle-lower seven member of Mesozoic Yanchang Formation in Ordos Basin, with the thickness 21–36m, burial depth 110–2900m and the exploration area 50 thousand square killometers. Shlae oil have five typical geological characteristics. (1)the organic-rich shale developped in the semi-deep ro deep lacustrine deposit, with I-type and II1-type kerogen, Ro 0.7–1.1%, TOC 1.4–25.6%, S1 1.2–11.6mg/g, chloroform asphalt A 0.2–1.2%, pyrite content 5.4–34.5%, and specially the hydrocarbon generation potential of shale is about five times of that of the mudstone; (2) laminated structure appeared commonly in the shale, pore-throats diameter are mainly 50–300nm, locally micro-sized pores, and nano-sized pore-throats and parallel bedding fractures are the main reservoir space; (3) higher brittle mineral content, with quartz, feldspar, calcite and dolomite 41%, and clay content lower than 50%; (4)lower formation pressure and lighter oil quality, with pressure coefficient 07–0.9, crude oil density 0.75–0.85 g/cm³, and viscidity 0.7–5mPas; (5) residual liquid hydrocarbon occurs in adsorption state and free state, with adsorption state in organic matters, adsorption state and free state in nano-sized pore-throats in pyrite, clay and brittle minerals, and free state in parallel bedding fractures. Organic-rich shale of Mesozoic Yanchang Formation in Ordos Basin, have “five higher” typical characteristics, respectively higher TOC, higher pyrite content, higher S1, higher chloroform asphalt A, and higher Gamma ray value. The beneficial shale oil distributiona area, with TOC higher than 2% and Ro higher than 0.7%, is about 20 thousand square killometers, and the preliminary resource potential is about 1 billion tons.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015