川南自贡区块构造位置位于四川盆地威远斜坡南翼,为北西—南东向单斜坡。该区目的层上奥陶统五峰组—下志留统龙一₁亚段为深水陆棚相富有机质黑色页岩沉积,储层纵向非均质性较强。水平井页岩“甜点段”钻遇程度的不同造成了测试效果的差异。为明确该区页岩最佳靶体纵向分布、指导水平井钻井轨迹跟踪调整,基于地层小层划分,综合运用钻井、录井、测井及分析化验等资料开展储层精细评价,并利用产气剖面资料评价靶体对页岩气水平井产能的影响。研究结果表明：①受沉积和构造作用的双重影响,目的层中龙一₁¹小层下部页岩段为最优的“地质—工程”双“甜点”;②生产测井分析表明,龙一₁¹小层下部具有最高的单位长度产气贡献率,是研究区的最佳靶体;③水平井的龙一₁¹小层下部页岩有效压裂段长是影响自贡区块气井产能的关键因素。该研究成果将自贡区块最佳靶体纵向分布厚度由2~5 m精确到1~2 m,有效支撑了页岩气产能评价工作,为该区块实现页岩气规模效益开发奠定了基础。

Zigong Block, which is located in the southern side of Weiyuan Slope in Sichuan Basin, is a monocline in NW-SE direction. O₃w-S₁l^1-1 is the target layer of that block, which develops black shale with rich organic matters in deep-water continental shelf, while the longitudinal heterogeneity of the reservoir is strong. Different penetration degrees in the sweet spot of horizontal shale well lead to different testing results. In order to determine the longitudinal distribution of the optimal shale target and guide the tracking and adjustment of horizontal well drilling trajectory, based on stratigraphic subdivision, fine evaluation of reservoir is carried out by the comprehensive data of drilling, logging, well testing and laboratory analysis. Meanwhile, the gas production profile data are used to evaluate the impact of the target on shale gas productivity of the horizontal wells. The research results show that: ①Under the influence of both sedimentation and tectonics, the lower part of S₁l^1-1-1 are the optimal “sweet spots” for both geology and engineering among target layers; ②The production well logging data indicate that, the lower part of S₁l^1-1-1shows highest gas production contribution of per unit length, which is the optimal target position of the research area; ③The effective fracking length of shale reservoir in the lower part of S₁l^1-1-1 for horizontal well is the key factor for gas well productivity in Zigong Block. Based on the above results, which supports the productivity evaluation of shale gas effectively, and sets the foundation for realizing large-scale and cost-efficient development of shale gas in that block, the longitudinal distribution thickness of the optimal target in Zigong Block is accurate from 2~5 m to 1~2 m.