科研之友
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摘要
With world-leading shale gas resources, ongoing economic growth, and concerns for energy security, China has been embarking on an ambitious shale gas development program. However, nearly 30 years of American experience in exploration and development indicates a steep initial production decline and low overall recovery of hydrocarbons; this can be implicated in the complexity of nanopore structure (geometry and connectivity) and Dalmatian wettability of shale formations. In this study, we first develop a suite of nano-sized tracers, with different sizes and reactivities, in both hydrophilic brine and hydrophobic n-decane fluids in order to study the coupled nanopore connectivity and wettability of shale. These wettability-tracers are then used for Longmaxi Formation, as core and surface outcrop samples, the leading gas-producing shale formation in China. Fluid droplet wettability tests indicate a dual wettability pattern, with more tendency of oil-wetting than waterwetting, from heterogeneous distribution of shale composition and diagenesis history. Coupled with pore structure characterization from mercury intrusion capillary pressure analysis, we then conduct tests of tracer imbibition into initially dry shale, as well as tracer diffusion into fluid-saturated shale, followed with laser ablation-ICP-MS elemental mapping for the presence and distribution of tracers in shale. The imbibition and diffusion tests use tracer-bearing wettability fluids (brine or n-decane) to examine the intertwined relationship of nanopore connectivity and wettability. Overall findings from the above innovative approaches indicate the limited connectivity for water-wetting pore systems (>50-100 nm pore-throat diameters), and probable entanglement of sub-nano-sized molecules in smaller (similar to 10 nm) nano-sized pore-throats of better-connected oil-wetting pore networks.
- 出版日期2017-9
- 单位重庆科技学院; 中国石油天然气股份有限公司勘探开发研究院; 中国地质大学（武汉）
