Perforation optimization of layer-penetration fracturing for commingling gas production in coal measure strata

Abstract

Optimization of fracturing perforation is of great importance to the commingling gas production in coal measure strata. In this paper, a 3D lattice algorithm hydraulic fracturing simulator was employed to study the effects of perforation position and length on hydraulic fracture propagation in coal measures of the Lin-Xing block, China. Based on field data, three lithologic combinations are simulated: 1) a thick section of coal seam sandwiched by sandstones; 2) a thin coal seam layer overlay by gas-bearing tight sandstone; 3) two coal seams separated by a thin layer of sandstone. Our simulation shows that perforation position and length in multi-layer reservoirs play a major role in hydraulic fracture propagation. Achieving maximum stimulated volume requires consideration of lithologic sequence, coal seam thickness, stress states, and rock properties. To improve the combined gas production in coal measure strata, it is possible to simultaneously stimulate multiple coal seams or adjacent gas-bearing sandstones. In these cases, perforation location and length also significantly impact fracture propagation, and therefore should be carefully designed. Our simulation results using 3D lattice algorithm are qualitatively consistent with laboratory physical simulation. 3D lattice models can be used to effectively simulate the fracture propagation through layers in coal measure strata. The numerical results provide guidance for perforation optimization in the hydraulic fracturing of coal measure strata.