Formation mechanism, geological characteristics and development strategy of nonmarine shale oil in China

TLDR

Shale oil is a mature conventional–unconventional resource stored in organic‑rich, nano‑pore shales deposited in semi‑deep to deep lake environments, where kerogen type I/IIA, TOC > 2 %, and effective thickness > 10 m provide the primary reservoir space and key parameters such as brittleness, viscosity, pressure, and retained quantity. The study aims to analyze continental shale oil in China—its sedimentary environment, reservoir space, geochemistry, and accumulation mechanism—and to propose a three‑step development strategy. Key production technologies include horizontal‑well volume fracturing, natural fracture reformation, and coarse‑grain injection to create artificial reservoirs, forming the basis of the proposed three‑step development strategy. China’s continental shale oil resources are estimated at 3–6 × 10^8 t, and, following North American marine shale successes, industrialization is likely to commence soon.

Abstract

As an important type of “conventional–unconventional orderly accumulation”, shale oil is mature oil stored in organic-rich shales with nano-scale pores. This paper analyzes and summarizes elementary petroleum geological issues concerning continental shale oil in China, including sedimentary environment, reservoir space, geochemical features and accumulation mechanism. Mainly deposited in semi-deep to deep lake environment, shale rich in organic matter usually coexists with other lithologies in laminated texture, and micron to nano-scale pores and microfractures serve as primary reservoir space. Favorable shale mainly has type I and IIA kerogens with a Ro of 0.7%–2.0%, TOC more than 2.0%, and effective thickness of over 10 m. The evolution of shale pores and retained accumulation pattern of shale oil are figured out. Reservoir space, brittleness, viscosity, pressure, retained quantity are key parameters in the “core” area evaluation of shale oil. Continuously accumulated in the center of lake basins, continental shale oil resources in China are about 30×108–60×108 t by preliminary prediction. Volume fracturing in horizontal wells, reformation of natural fractures, and man-made reservoir by injecting coarse grains are some of the key technologies for shale oil production. A three step development road for shale oil is put forward, speeding up study on “shale oil prospective area”, stepping up selection of “core areas”, and expanding “test areas”. By learning from marine shale breakthroughs in North America, continental shale oil industrialization is likely to kick off in China.