Exploration of coal-measure gas reservoir characteristics and reforming technology in Lishu Mine Field of Jixi Basin

The superimposed combination of coalbed methane，tight sandstone gas and shale gas in coal measures has great development potential，but it has the characteristics of diverse occurrence types，complex accumulation combinations，and large differences in reservoir mechanical properties and engineering responses. Exploring coal-measure “three-gas” co-exploration and co-production technology is an inevitable requirement for realizing the economic and efficient development of coal-measure gas. Studying the characteristics of coal-measure gas reservoirs，reasonably selecting target horizons，determining perforation positions，optimizing fracturing construction techniques and parameters，and achieving balanced transformation of multiple types of gas-producing layers，can minimize interlayer interference and fully release the overall gas production potential of the gas-producing layer group. In this paper，the interbedded section of the Cretaceous Chengzihe Formation，the coal-measure argillaceous rock and the coal-measure tight sandstone interbedded in the HJD1 well of Lishu minefield in Jixi Basin was used as the research object. The characteristics of unconventional gas reservoirs in coal measures were systematic studied，combined production layers have been optimized，segmented perforation and hydraulic fracturing techniques that match the characteristics of multiple types of coal-measure reservoirs have been explored，and the fracturing construction process and process parameters have been optimized. The results show that the thin interbedded section between the coal seams of the Chengzihe Formation and the dark mudstone and sandstone has high gas content，good hydrocarbon generation potential，and superior coal-measure gas resource conditions; The following seams have been selected：① coal seams and coal seams，② coal-measure shale，coal measures tight sandstone and coal seam，③coal-measure shale-coal-measure tight sandstone and other lithology combination target intervals for combined mining; the optimized construction plan is to increase the length of the perforation section (1.8-6.3 times the thickness of the coal seam，1.2-3.0 times the thickness of sand and mudstone gas-bearing seam)，increase the proportion of front fluid (45%-55%)，adopt “large liquid volume (1 200-1 800 m3)，large sand volume (5.7-10.4 m3/m)，large displacement (9.33-10.28 m3/min)，high sand ratio (7.9%-9.4%)，high injection pressure (45.0～46.7 MPa)，multi-stage stepped sand adding” and ball-throwing partial pressure construction technology，realizing well-balanced reformation of reservoirs through differential fracturing of multiple types of coal-measure reservoirs，achieving a good volumetric fracturing reformation effect. The research work is of reference significance for the efficient exploration and development of coal-measure gas in areas where coal seams are developed.