Regional Migration of Hypersaline Brines in Sedimentary Basins

沉积盆地孔隙流体区域运移的驱动机制是沉积物压实作用和地形作用。先前的分析表明，除非流体流动在空间或时间上受到限制，否则这两种机制都可能难以解释上述一些地质观测结果。具体而言，孔隙流体的热含量或流速或两者都不足以使压实驱动流动在区域尺度上产生热孔隙流体的运移。地形驱动的流动可能在区域范围内产生温暖的孔隙流体，但会导致流体中含盐成分的耗竭。我们拟开展为期两年的高盐盐水区域运移研究：①建立适合盆地条件下高盐盐水的PTX状态方程，研究盐度对沉积盆地孔隙水流动的控制作用；(2)研究暖盐水聚焦或集中流动的各种机制，包括：孔隙流体的幕式排出、流体沿含水层或断层流动、基底或地表构造对流体的偏转或聚焦以及三维流动；(3)将研究结果应用于阿拉斯加Colville盆地和墨西哥湾北部地区孔隙流体的区域运移。高盐盐水在数百公里范围内通过沉积盆地的区域迁移被认为是解释一些重要地质观测的一种机制。其中包括：北美古生代碳酸盐岩中的再磁化作用、粘土矿物成岩作用、高压高温流体包裹体、油气和密西西比河谷型铅锌矿床的分布。

The most widely accepted driving mechanisms for regional migration of pore fluids in sedimentary basins are sediment compaction and topography. Previous analyses indicate that both mechanisms have potential difficulties explaining some of the above geologic observations unless the fluid flow is spatially or temporally restricted. Specifically, heat content of pore fluids or flow rates or both are not sufficient for compaction driven flow to produce migration of warm pore fluids on a regional scale. Topographically-driven flow may produce warm pore fluids on a regional scale, but would result in depletion of saline components of fluids. We propose to carry out a two year study on the following aspects of regional migration of hypersaline brines: (1) develop suitable PTX equations of state for hypersaline brines under basinal conditions and examine the effects of salinity in controlling pore water flow in sedimentary basins; (2) examine various mechanism for focusing or concentrating flow of warm, saline brines, including: episodic expulsion of pore fluids, fluid flow along aquifers or faults, deflection or focusing of fluid flow by basement or surface structures and three-dimensional flow; and (3) apply these results to the regional migration of pore fluids in the Colville Basin, Alaska and the Northern Gulf Coast. The regional migration of hypersaline brines over hundreds of kilometers through sedimentary basins has been suggested as a mechanism to explain a number of important geologic observations. These include: remagnetizations found in Paleozoic carbonates of North America, clay mineral diagenesis, inclusions of high pressure, high temperature fluids, and distribution of oil, gas and Mississippi Valley-type lead-zinc deposits.