Concepts, characteristics, potential and technology of unconventional hydrocarbons: On unconventional petroleum geology

TLDR

Petroleum geology now divides into conventional and unconventional branches, the latter focusing on continuous hydrocarbon accumulations and stressing lithology, physical properties, brittleness, oiliness, source rock features, and stress anisotropy. The study aims to intensify development of tight gas and tight oil, build shale gas pilot plants, and advance shale oil research to unlock industrial reserves and boost production. The authors propose establishing an integrated unconventional oil and gas industrial system that includes geology, sedimentology, reservoir studies, seismic prediction, horizontal well fracturing, factory‑like operations, cost‑effective management, subsidies, and workforce training. The authors established low‑pore‑throat accumulation models, an L‑type production curve, and predictive production models, revealing that unconventional hydrocarbons are characterized by continuous, trap‑free reservoirs, lack of natural Darcy flow, and constitute roughly 80 % of global hydrocarbon resources, with China holding 240 × 10⁸ t of oil and 100 × 10¹² m³ of gas.

Abstract

Petroleum geology is evolving into two branches, conventional petroleum geology and unconventional petroleum geology, with the latter becoming a new theoretical frontier in the petroleum industry. The core of conventional hydrocarbon geological study is based on identifying the match between source rock, reservoir, caprock, migration, trap, preservation and timing; the core of unconventional hydrocarbon geological study evaluates if the oil and gas is part of a continuous accumulation, where stress is placed on the evaluation of "lithology, physical properties, brittleness, oiliness, source rock features, stress anisotropy" and their configuration. The oil and gas accumulation mode and theoretical formula at various low limits of pore throat diameter have been established, as well as the "L" type production curve. Theoretical production prediction models for unconventional oil and gas, and formation mechanism and development patterns for unconventional oil and gas are being revealed. The connotation, characteristics, potential and technology for unconventional oil and gas have been observed, and two key marks to identify unconventional hydrocarbon have been put forward: (1) continuous distribution of hydrocarbon-bearing reservoirs over a large area, with no obvious trap boundary; and (2) no natural stable industrial production, and no obvious Darcy flow. Systematic research shows that the proportion of global unconventional to conventional hydrocarbon resources is 8:2, in which the unconventional oil is almost equal to conventional oil, and the unconventional gas is about 8 times that of conventional gas. In China, unconventional oil resources are about 240×108 t and unconventional gas resources are about 100×1012 m3. In recent years the development of tight gas and tight oil should be strengthened to realize industrial reserves and increase production. Construction of shale gas pilot plants and shale oil research should be strengthened. Unconventional oil and gas industrial systems and research should be set up, including unconventional hydrocarbon geology, fine particle sedimentology, unconventional reservoir geology, seismic reservoir prediction, massive fracturing of horizontal wells, "factory-like" operation, low cost management and subsidy policy and personnel training.