川西前陆盆地流体的跨层流动

本文讨论了川西前陆盆地气田区上三叠统和侏罗系地层水K+ +Na+ 、Ca2 + 、Mg2 + 、Br-与Cl-离子、矿物 (胶结物和充填物 )碳氧同位素和水的氢氧同位素成分组成以及相互关系。气田区上三叠统流体来源以地层海陆相沉积物质为主 ,并与渗流水混合 ,形成“下部流体”。有气藏的侏罗系内流体 (称“上部流体”)与“下部流体”的水化学和同位素组成相近 ,且具有同一演化趋势 ,表明它来源于下部流体并与侏罗系层内的渗流水发生过混合作用。本文提出该气田流体具跨层流动、二次混合演化特征 ,认为大规模的流体对流混合促进了上三叠统内天然气的运移聚积 ,在三叠系内有利构造圈闭中形成原生或残留气藏并向上运移 ,在侏罗系内有利圈闭中形成“次生”气藏。

CROSS-FORMATIONAL MIGRATION OF FLUIDS IN THE COMPACT SANDSTONE-TYPE GAS FIELD,WEST SICHUAN FORELAND BASIN

The paper discusses the migration and variation of fluids from the Upper Triassic and Jurassic series in a compact sandstone-type natural gas field, West Sichuan Foreland Basin, based on the concentrations of and relationships among K ++Na+, Ca 2+, Mg 2+, Br - and Cl -, and hydrogen-oxygen isotopes(δD,δ 18O) of formation waters, as well as carbon-oxygen isotopes(δ 13C,δ 18O) of the minerals (cements and fissure veins of the Upper Triassic formation). The result demonstrates that the original fluid in the UpperTriassic series was derived from the series itself (marine-land sediments which are the source strata of hydrocarbon), then mixed with vadose water to form "lower fluid", but the fluid in the Jurassic system with natural gas pools came directly from or mixed with the "lower fluid" of the underlying Triassic system, in terms of their similar composition and variation trend in geochemical and isotopic geology. Under the condition of large pressure difference, extensive migration of the formation waters may take place and thus cause the transport and accumulation of gas, forming"original" or "remnant" gas in favorable structure traces of the Upper Triassic series, and "secondary" gas in the Jurassic system.