Productivity prediction and gas production technology of superimposed coal measure gas in the eastern margin of Ordos Basin

Superimposed coal measure gas reservoirs are rich in the eastern margin of Ordos Basin. Combined production is an effective method to solve the problem of low single-layer productivity and poor comprehensive economic benefits. In view of the lack of in-depth research on the geological conditions of coal measure gas reservoir and the coupling flow mechanism in the development process, it is difficult to reveal the coupling mass transfer characteristics in the production process. Based on the Permo Carboniferous coal measure gas reservoir in the Linxing area, a high-precision geological model of multi-layer superimposed gas reservoir is established through the multiple facies control modeling technology, combined with sedimentary micro-facies division and sand body control degree analysis. Based on the geological model and the classification standard of static layer formation combination, the favorable development gas formation combination is divided. At the same time, the coupling mass transfer chain model of coalbed methane and tight gas is established according to the multi-scale mass transfer mechanism of coalbed methane and tight gas micropore-fracture-macrofracture. The research results reveal the mass transfer mechanism of coal measure gas combined production under the triple coupling action of interbedding connectivity, short-range coupling and long-range disturbance, in which the coupling action reduces the initial effect of the combined production of coalbed methane and tight gas, but is conducive to the long-term stable production goal. Furthermore, the numerical simulation method is used to clarify the dynamic combined production characteristics under the conditions of different coupling relations, optimize the horizon combination and replacement scheme of static production layers, and put forward the combined layer drainage process design and equipment selection method under the conditions of the same wellbore combined production and separate pressure combined production. The research on the wellbore process determines the production lower limit of the long-distance interference of gas and water in combined production. The study area takes the Shan 2 tight gas as the gas lift gas source, and cooperates with the drainage and depressurization of the Tai 2. After the desorption of the coal seam gas, the joint production of “Shan 2 + Tai 2 + Ben 2 s” can be realized, and the alternative scheme of the joint production of the He 4 and He 8 tight gas is the best. At the same time, the research shows that the static production combination does not consider the dynamic interference in the production process of different gas reservoirs, and the optimization method of production combination needs to be dynamically optimized from the static combination. The high-efficiency combined production model of coal measure gas is explored, which can lay a theoretical foundation for the research of combined production and production increase of coal measure gas in the eastern margin of Ordos Basin, and promote the rational use and efficient development of deep coal measure gas. © 2022 China Coal Society. All rights reserved.