部分压开页岩气井产能递减分析

ANALYSIS ON PRODUCTIVITY DECLINE OF PARTIAL OPEN FRACTURED WELLS IN SHALE GAS RESERVOIRS

水力压裂技术已广泛应用于增加页岩气井的产量,由于实际页岩储层厚度普遍较大,以现有的压裂技术难以完全压开储层。因此,针对页岩气解吸、扩散和渗流特征,建立了部分压开页岩气井产能模型,分别运用Laplace变换、Fourier变换和Duhamel原理,并通过Stehfest数值反演求解产能模型,绘制了部分压开页岩气井产能递减曲线,并分析了压开程度、解吸系数、无因次储容系数、无因次解吸时间、裂缝中心位置对产能递减曲线的影响。研究表明:页岩气井的产量随着压开程度增加而增大;吸附气解吸量随着解吸系数的增大而增大,由于吸附气的解吸,气井产量递减越慢;无因次解吸时间越小,页岩气解吸发生得越早;裂缝中心越靠近储层中心,部分压开页岩气井产量递减越慢。因此,对页岩气井实施压裂时,应该尽量增大储层的压开程度并且尽量使压开裂缝中心靠近储层的中心位置。

In order to realize the efficient development of shale gas reservoirs,hydraulic fracturing has been obtained the widespread application in the development process of shale gas reservoirs. However,the reservoir is difficult to be completely open in practice because the thickness of the shale gas reservoir is always large. Therefore,according to the characteristics of desorption,diffusion and seepage,a productivity model of partial open fractured wells in shale gas reservoirs has been established.And the productivity model was calculated by using Laplace transform,Fourier transform and the principle of Duhamel in combination with Stehfest numerical inversion algorithm. The productivity decline curves of partial open fractured wells in shale gas reservoirs were plotted. The influences of the open degree,the desorption coefficient,the dimensionless storativity ratio,the dimensionless desorption time and the center position of the crack on the productivity decline curves were analyzed. The study shows that the larger the open degree is,the larger the output of a partial open fractured well is,and the larger the desorption coefficient is,the larger the desorption quantity is,the slower the output degression speed of a partial open fractured well in a shale gas reservoir becomes. The starting time of desorption depends on the magnitude of the dimensionless desorption time. The smaller the dimensionless desorption time is,the earlier the starting time of desorption becomes. The center position of the crack has influence on the productivity decline curves of partial open fractured wells in shale gas reservoirs. The smaller the distance between the center position of the crack and the center position of the reservoir is,the slower the output degression speed of a partial open fractured well becomes. Therefore,it is important for implementing the hydraulic fracturing to increase the open degree and make the center position of the crack near the center position of the reservoir.