四川盆地威远地区页岩气优质储层精细刻画与靶窗优选

中国石油化工股份有限公司威远页岩气勘查区块的构造位置位于四川盆地威远古隆起与自流井背斜所夹持的白马镇向斜,该区上奥陶统五峰组—下志留统龙马溪组一段为深水陆棚相暗色富有机质页岩沉积,地球物理测井岩电特征纵向差异明显,储层非均质性较强。为了指导该区页岩气水平井靶窗优选及钻井轨迹跟踪调整,基于测井小层划分、岩心纹层精细刻画、高精度地球物理预测以及沉积微相成因分析等方法,通过细化储层分类评价其参数指标,预测页岩气储层"甜点",在此基础上进行水平井靶窗优选及轨迹设计,进而评价水平井靶窗对页岩气产能的影响。研究结果表明:①该区五峰组—龙一段底部优质页岩段发育3种类型的纹层,纵向上交错叠置,反映了沉积环境和储层品质的微观差异;②可以将该区的页岩气储层划分为优质储层、较好储层、一般储层和差储层;③龙马溪组底部2—31小层为生物成因沉积微相,储层具有高有机碳含量、高孔隙度、高脆性指数、高含气性、低地应力差值等"地质+工程"甜点的特征,确定其为优质储层段;④实钻结果表明,水平井靶窗位置的选择对于单井页岩气产能的影响较大,优质储层钻遇率是获得页岩气高产的关键地质因素。该研究成果支撑了页岩气产能评价工作,为该区块实现页岩气商业开发奠定了基础。

Fine characterization and target window optimization of high-quality shale gas reservoirs in the Weiyuan area,Sichuan Basin

Sinopec's Weiyuan Shale Gas Block is structurally located at the Baimazhen syncline held by the Weiyuan paleo-uplift and Ziliujing anticline in the Sichuan Basin. In this block, the Wufeng Fm of Upper Ordovician–Longmaxi Fm of Lower Silurian is an organic-rich dark shale deposit of deep-water shelf facies, whose litho-electric characteristics of geophysical logging are obviously different vertically and reservoir heterogeneity is strong. For providing a guidance for target window optimization and drilling trajectory tracking and adjustment of horizontal wells in the Weiyuan Shale Gas Block, parameter indexes were evaluated by refining the reservoir classification based on well logging subdivision, fine characterization of core laminae, high-precision geophysical prediction and genetic analysis of sedimentary microfacies. Furthermore, the "sweet spots" of shale gas reservoirs were predicted. Then, the target window was optimized and the trajectory of a horizontal well was designed. Finally, the effects of the target window of a horizontal well on shale gas productivity were evaluated. And the following research results were obtained. First, three types of laminae are developed in the high-quality shale reservoir at the bottom of Wufeng Fm–Long 1 Member, and they are vertically staggered and overlapped, which reflects the microscopic difference of sedimentary environment and reservoir quality. Second, shale gas reservoirs in this block can be divided into high-quality reservoirs, better reservoirs, general reservoirs and poor reservoirs. Third, the sublayer 2–31 at the bottom of Longmaxi Fm is biogenic sedimentary microfacies and it has the characteristics of "geological + engineering" sweet spot, e.g. high TOC contents, high porosity, high brittleness, high gas content and low in-situ stress difference, so it is classified as a high-quality reservoir. Fourth, actual drilling results show that the location selection of the target window of a horizontal well has a significant impact on single-well shale gas productivity, and the penetration rate of a high-quality reservoir is the key geological factor to achieve high-yield shale gas. The research results provide support for the evaluation of shale gas productivity and lay a foundation for the commercial development of shale gas in the Weiyuan Shale Gas Block.