Effects of perforation degree and deployment position of multilateral horizontal wells on gas production from inclined clay hydrate reservoirs
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摘要:
南海天然气水合物（以下简称水合物）较多赋存于凹凸起伏的泥质地层中。针对实际倾斜水合物储层展开多分支井产能研究十分必要。以南海北部神狐海域X01站位实际地质参数和地形参数为依据，利用TOUGH+HYDRATE水合物产能预测软件和经过验证的建模新方法，建立了代表实际情况的倾斜泥质水合物储层模型，探讨了多分支井射孔程度对开采产能的影响，对比了位于储层不同构造位置（即构造低部位、倾斜部位和构造高部位）的多分支井的产能差异，确定了优势开采井型和最佳布井位置。结果表明，相比于仅水平分支射孔的多分支井，水平分支和垂直主井同时射孔的多分支井更利于水合物分解产气。但垂直主井的打开长度不宜过长，垂直主井与水平分支的打开长度比值介于0.5～1.0最利于提高气水产出比。泥质水合物储层的地层倾角影响多分支井的开采产能，将多分支井布设在储层构造低部位的水平位置更利于实现水合物长期高效开采。
Abstract:Natural gas hydrate (NGH) is generally disseminated in inclined mud sediments in South China Sea (SCS), China. It is of great significance to investigate the production performance of multilateral horizontal wells in actual inclined NGH reservoirs. We implemented a real 3D inclined clay hydrate reservoir model based on geological and topographical data from the site X01, Shenhu Area, SCS, to simulate the production performance of multilateral horizontal wells with TOUGH+HYDRATE software and verified the modeling method. We studied the effects of perforation degree on the production performance of multilateral horizontal wells. The differences in production were compared when multilateral horizontal wells were deployed at different tectonic settings of NGH reservoirs (i.e., structural high position, inclined position, and structural low position). The optimal well configuration and placement position were determined. Results show that multilateral horizontal wells that are perforated simultaneously in horizontal branch and vertical main well are beneficial to enhance NGH dissociation and gas production. However, the perforation section of vertical main wells should not be too long. The optimal length ratio of vertical main well and horizontal branch is 0.5～1.0. Moreover, the inclination of the hydrate reservoirs affects significantly the production performance of multilateral horizontal wells. Comparatively, deploying multilateral horizontal wells at horizontal places at low structural positions of clay hydrate reservoirs is conducive to long-term and efficient production of NGH.
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图 1 中国南海珠江口盆地和X01站位所在水合物储层的厚度示意图(A—B)，多分支井结构示意图(C)，基于实际地形参数和地质参数建立的倾斜3D储层模型及多分支井在储层不同构造部位的布设示意图(D)
Figure 1.
参数 数值 参数 数值 储层基础参数 上覆盖层厚度/m 116.5 颗粒密度/(kg∙m−3) 2650 水合物储层厚度/m 76 地温梯度/(℃/100 m) 5.46 下伏地层厚度/m 120 热导率(湿)/(W∙m−1∙℃) 2.917 储层孔隙度/% 34.50 热导率(干)/(W∙m−1∙℃) 1.00 储层绝对渗透率/(10−3μ㎡) kx = ky = kz = 0.22 压缩系数/Pa−1 1.00×10−8 水合物饱和度/% 34.00 比热容/(J∙kg−1∙℃−1) 1000 X01站位处水深/m 1309.75 孔隙水盐度/‰ 3.05 相对渗透率模型(Relative permeability model) [39] KrA =（SA*）n KrG =（SG*）nG SA*=（SA−SirA）/（1−SirA） SG* =（SG −SirG）/（1−SirA） SirA 0.50 nG 3.00 SirG 0.05 n 5.00 孔隙水压力模型(Capillary pressure model) [42] Pcap = −P0[（S*）−1/λ−1]1−λ S* =（SA−SirA）/（SmxA−SirA） P0/Pa 105 SmxA 1.00 λ 0.15 SirA 0.50 
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