Key Technology of Efficient Exploitation of Coalbed Methane in Qinshui Basin of CNOOC

DOI: 10.14800/IOGR.1274

Abstract

Three key technologies have been developed for the development of coalbed methane in Qinshui Basin. The first technology is the gas content analysis technology coupled with isothermal adsorption theory and production dynamics. By fitting bottom-hole flow pressure and critical desorption pressure of coal reservoir, combined with the isothermal adsorption curve of coal reservoir, the gas content of the reservoir can be accurately predicted. This technique provides important geological parameters for evaluating coal reservoirs. The second technology is production system optimization technology based on reservoir seepage mechanism and numerical simulation analysis. Velocity sensitive response, stress sensitive effect and gas-water two-phase flow are considered in the process of production system optimization. By understanding the main contradictions in different production and discharge stages of coalbed methane wells and taking the final cumulative gas production and peak gas production as optimization objectives, the quantitative optimization method of coalbed methane drainage and production system is formed. One optimization system for each coalbed methane well and one optimization system for each day has been realized. This technology is used throughout the entire production cycle of a coalbed methane well. The third technology is the efficient development technology of horizontal well in coal seam with fractured coal structure.Through numerical simulation study, it is clear that No. 15 coal seam in Panhe Block is suitable for integrated horizontal well development. In the early stage of horizontal well drilling, problems such as wall instability, drilling depth of some wells is not up to the design, and the length of horizontal section of real drilling is not up to the design. Aiming at this problem, the stability model of borehole wall of Panhe River is established by using the four-dimensional geostress modeling technique. The model reveals that the collapse pressure of horizontal wells is higher than that of vertical wells, and complex accidents such as collapse block are more likely to occur. In view of this feature, suspension agent, drainage aid and inhibitor are selected to improve the return of pulverized coal pressure, promote the fracturing fluid backflow, reduce the viscosity of mineral collision, and select a new type of active water fracturing fluid system. The successful application of the three key technologies provides a strong support for the efficient development of coalbed methane in Qinshui Basin, and also provides a technical reference for the efficient development of other coalbed methane basins.