Formation, distribution, sweet spot evaluation and development prospect of coal-measure gas in China

In order to provide references for the exploration and development of coal-measure gas in China, this paper constructs an evaluation system of sweet areas/sections of coal-measure gas based on the recent research results. The system comprises 4 elements involving 15 indexes. And the following research results are obtained. First, the first element refers to the geological parameters of sweet spot in coal measures. As for this element, attention shall be paid to evaluating the reservoir properties of coal measure and the deformation evolution, scale and preservation conditions of geomechanical layers. Second, the second element is the seepage capacity of interbedded coal-measure gas. It is necessary to deeply reveal the accumulation mode of coal-measure gas, the dynamic conversion of free gas and adsorbed gas, the development characteristics of natural fractures, the cross-layer seepage in interbedded structures, and the seepage heterogeneity in composite fault systems. Third, the third element is the gas content evaluation. A gas content evaluation model which suits high-frequency cycle interbedded coal measures and matches with productivity releasing capacity shall be established to accurately assess the amount of coal-measure gas resources. Fourth, the fourth element is the commingled fracturing of coal measures. Attention shall be paid to evaluating rock mechanical properties, ground stress and brittleness, optimizing the commingled fracturing effect by virtue of the dynamic monitoring technology, and preparing a four-dimensional fracturing technology scheme. Fifth, to select the sweet spot of coal-measure gas, it is necessary to take into account the properties of hydrocarbon source, reservoir, gas content, fracture, reservoir stimulation and economy comprehensively. In addition, coal-measure gas presents the following development trend in China. First, deep coalbed methane (coal rock gas) and bauxitite gas will become the new objects and directions of coal-measure gas exploration and development. Second, the theory of unconventional gas accumulation in deep coal measures will be gradually formed. Third, it is necessary to strengthen the researches on multi-scale pore and fracture characterization, cross-layer seepage, commingled fracturing for permeability improvement, and novel numerical-intelligence production model of natural gas plant. Fourth, it is necessary to integrate multiple disciplines to comprehensively evaluate the sweet spots of various coal-measure gas resources, so as to assist the exploration and development of deep coal-measure gas. © 2024 Natural Gas Industry Journal Agency. All rights reserved.