钻孔间距对水力压裂促抽煤层瓦斯的影响

针对定量确定合理钻孔间距困难问题，基于损伤力学和多场耦合理论，建立了水力压裂和瓦斯抽采的煤层流固耦合模型，包括和水运移场、应力场以及孔隙度、渗透率演化方程，并采用Comsol联合Matlab求解，研究了不同钻孔间距时压裂和抽采过程中煤层弹模、损伤值、渗透率、瓦斯压力、抽采量和压裂贯通时间的变化规律。结果表明:耦合模型可较准确地模拟煤层水力压裂和瓦斯抽采过程；压裂贯通时间与钻孔间距呈指数增长关系；在马堡煤矿，当钻孔间距为4~8 m时，压裂损伤区在抽采孔贯通，渗透率呈“n”型曲线，瓦斯抽采后，瓦斯压力迅速下降，抽采有效区随间距的增加而增大；当钻孔间距为9~12 m时，压裂损伤区未贯通，煤层渗透率呈“m”型曲线，抽采有效区随间距的增加而减小，与间距4~8 m相比，瓦斯抽采量较小。

Influence of spacing between boreholes on hydraulic fracturing to enhance coal seam gas extraction

Aiming at the problem that it is difficult to quantitatively determine the reasonable spacing between boreholes, a coal seam fluid-solid coupled model of hydraulic fracturing and gas extraction was established based on the damage mechanics and multi-field coupling theory, which included the equations of gas and water migration field, stress field and evolution of porosity and permeability. Through the solution by using Comsol combined with Matlab, the variation laws of coal seam elastic modulus, damage value, permeability, gas pressure, extraction amount and fracture breakthrough time during the fracturing and extraction processes with different spacing between boreholes were studied. The results showed that the coupled model can simulate the hydraulic fracturing and gas extraction processes of coal seam accurately, and the fracture breakthrough time increased exponentially with the spacing between boreholes. Under the conditions of Mabao coal mine, when the spacing between boreholes was 4-8 m, the fracture damage zone connected at the extraction borehole, the permeability presented a 'n' type curve, and after the gas extraction, the gas pressure dropped rapidly, and the extraction effective area increased with the increase of the spacing between boreholes. When the spacing between boreholes was 9-12 m, the fracture damage zone did not connect, the permeability presented a 'm' type curve, the extraction effective area decreased with the increase of the spacing between boreholes, and the gas extraction amount was smaller than that when the spacing between boreholes was 4-8 m.