致密砂岩气藏水平井参数优化

鄂尔多斯盆地致密砂岩气藏总体呈现储层横向变化快、纵向多层发育的地质特征,水平井有效规模开发难度较大。为提高其开发效果,基于对已投产水平井单井控制动态储量、递减率、产能等动态指标的精细评价,从沉积位置、储层厚度、钻遇储层长度、井段位置、轨迹类型、改造方式等方面入手,分析了苏里格气田某区块水平井开发指标的影响因素,并应用灰色关联法定量分析了各参数对水平井产气能力的贡献值。研究结果表明:钻遇储层长度对水平井产能的影响最大,其次是储层位置、沉积微相、储层厚度、轨迹类型,改造方式。结论认为,该区块致密气藏水平井开发设计应遵循以下原则:(1)部署应以心滩和河道中部微相为主;(2)优质砂体厚度大于8 m,横向展布相对稳定;(3)水平段长度在经济效益允许的条件下尽可能长;(4)轨迹类型以平直型为主;(5)改造方式以裸眼封隔器为主。

Optimization of key parameters for horizontal well development of tight sandstone gas reservoirs

In the Sulige Gas Field of the Ordos Basin, tight sandstone gas reservoirs are generally characterized by fast variation laterally and multi layers vertically, which brings challenges to horizontal well development. In this paper, some producing horizontal wells were finely evaluated in terms of their dynamic indicators such as well-controlled reserves, production decline rate and productivity. On this basis, the factors influencing the indexes of horizontal well development of tight sandstone gas reservoirs in a block of the Sulige Gas Field were analyzed from the aspects of deposition position, reservoir thickness, reservoir drilling length, hole section position, trajectory type and stimulation mode. Furthermore, the contribution of each parameter to horizontal well gas productivity was analyzed quantitatively by using the grey correlation method. The findings are as follows. First, the productivity of horizontal wells is affected most by the reservoir drilling length, followed by reservoir position, sedimentary microfacies, reservoir thickness, trajectory type and stimulation mode. Second, horizontal wells shall be designed according to the principles of deployment in the microfacies of point bar and middle channel, high-quality sand body with thickness over 8 m and in relatively stable lateral distribution, long horizontal section if possible economically, straight trajectory, and stimulation with open hole packer. These results have been successfully applied in the Sulige Gas Field. Especially, four deployment patterns are established, i.e., overall horizontal well development, stereoscopic horizontal well development, large-size cluster hybrid well development, and large-size cluster vertical & directional well development. The effective reservoir drilling ratio of drilled horizontal wells is more than 60%, the tested absolute open flow (AOF) of natural gas is higher than 40×104 m3/d, and single-well production of horizontal wells is 4 times that of vertical wells.