砂岩侵入体及其油气地质意义

北美加利福尼亚地区良好的露头和北海油田的成功勘探与开发为砂岩侵入体研究提供了范例.砂岩侵入体广泛发育于晚元古代一全新世的多种沉积体系中,以深水环境居多.侵入体岩性以浊积体的中砂岩—细砂岩最为常见,宿主层以泥岩、页岩为主.侵入体系统包括供源砂体、侵入(出)体、宿主层和断裂体系4个构成要素和砂岩脉、砂岩床、砂岩柱、侵出体和...

Sand injectites and its petroleum geological significances

The good outcrops exposed along the California orogenic belt as well as successful exploration & development provide examples for the study of sandstone injections (injectites). Sandstone injections are widely developed in a variety of sedimentary systems from the Late Proterozoic to the Holocene of which deep-water systems are the most common ones. The lithology of injection is more frequently fine to medium-grained sandstone in turbidite fans, and the host layers are mainly mudstone and shale. Sand injections are comprised of 4 components including parent units, host strata, sand intrusion/extrusion, and the fracture systems and 5 types of sand dikes, sand sills, and columns/sand pillars, sand volcanos and injection complexes. The geometries of sand injection mainly consist of 3 types like saucer-wing shaped, conical shaped and crestal complex, and the top of the intrusion often develops mound shape. The interior part of sand injection is often structureless or laminated, with erosion boundaries and mass mud clasts, like a jigsaw. The formation conditions of intrusion include unconsolidated sand body, low-permeable overlain layers, pore fluid overpressure and dominant channel of the sand body. Seismic liquefaction, disequilibrium compaction, overburden, regional tectonic stress, and fluid flow are the most common triggering mechanisms. The formation process of intrusive body includes 5 processes:pore fluid overpressure, sand liquefaction, hydraulic fracturing and fluidization, sand injection and redeposition. Sand injections increase reservoir volume, link sand bodies together like conduits, and form injection traps. Sand injections can also be used to predict regional stress fields, but may also lead to failure of seals and water channeling. The determination of injecting time, geological process after injection and the deterministic study of triggering mechanisms are facing challenges. Interdisciplinarity, virtual outcrop, simulation experiments, and numerical simulation technology will be the future development direction.