Introduction to the special issue of unconventional hydrocarbon research

Abstract

Unconventional hydrocarbon research has developed rapidly in the recent years. In order to review the advances in unconventional hydrocarbon research in the areas of reservoir geology, geophysics, engineering, and economic evaluation, the Unconventional Natural Gas Institute (UNGI) of China University of Petroleum (Beijing) was invited to organize this special issue. Papers in this special issue are mainly about tight oil and gas, shale oil and gas, and coalbed methane, which are the main types of unconventional hydrocarbon. In the area of geology and accumulation mechanisms, Song et al. divided unconventional oil and gas into different types based on relationships between source rock evolution and different unconventional reservoirs and further noted that the fundamental difference between unconventional and conventional hydrocarbons is the driving force. Xiao et al. discussed the controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in south China, and established geological and loss models of shale gas for uplifted/folded and faulted/folded areas. Jiang et al. identified three types of tight sandstone gas reservoirs according to the timing of coupling between the two phases of gas charging and reservoir tightening, and clarified the controlling factors, accumulation mechanisms and modes of different types of tight gas reservoirs. Zou et al. optimized the evaluation parameters and standards of the tight oil ‘‘sweet spots’’ which are significant for the exploration of tight oil in China. In the area of geophysical exploration, Yin et al. proposed a constrained basis pursuit inversion (BPI) method for stably estimating the Young’s modulus and Poisson’s ratio, and effectively predicting the brittleness of unconventional reservoirs. In the area of hydraulic fracturing, Zeng et al. used the finite element method to quantify the stress distribution and investigated the controlling mechanism of the stress distribution of multi-stage hydraulic fracturing and fracture expansion. Ge et al. discussed the interaction between hydraulic fracturing fluids and shale matrix, clarified the mechanism of low flowback efficiency of fracturing fluids, and established its relationship to gas productivity. In the area of development and economic evaluation, Hu et al. discussed the pore structure of typical American and Chinese shales and investigated the effect of pore structure on the decline of shale gas well production. Wang et al. discussed the influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs. Zhang et al. proposed a model of hydraulic fracture in tight oil reservoirs by using a combined finite and discrete element method to direct the hydraulic fracturing of tight reservoirs. Tang et al. quantitatively divided the coalbed methane well-production process into four stages and quantitatively characterized the coal reservoir permeability change in different stages. Zhang et al. simulated the absolute adsorption and excess adsorption capacity of medium rank coal to CO2, CH4, and C2H6 gas using molecular dynamics, and provided a theoretical support for improving coalbed methane recovery using CO2 injection. Luo et al. applied the discounted cash & Yan Song sya@petrochina.com.cn