致密碎屑岩储层天然气成藏的古压控制作用

CONTROL OF PALEOPRESSURE OVER NATURAL GAS FORMATION IN TIGHT CLASOLITE RESERVOIRS

川西上三叠统碎屑岩储层是一套低孔渗，高含水饱和度，具高异常地层压力的致密砂泥岩层。据流体压力和储量将气藏划分为超高压小储量型（Ⅰ）、高压大储量型（Ⅱ）和正常－过渡压较大储量型（Ⅲ）３种类型。古压力的形成演化对成藏起控制作用，继承性生气增压及挤压增能，以有限的空间聚集油气可以形成超高压小储量型（Ⅰ）气藏；长期持续增压促使远距离捕集扩大圈闭累加聚气规模，是高压大储量型（Ⅱ）气藏形成的主要原因；而构造缝及高压扩大缝发育，早期相对富集，后期改造适度则是正常－过渡压较大储量型（Ⅲ）气藏形成的基本模式。

Upper Triassic clasolite reservoirs in West Sichuan are a set of tight sand-mud rocks with low porosity-low permeability, high aqueous saturation and abnormal high pressure. According to their fluid pressures and gas reserves, the reservoirs could be divided into superhigh pressure-low reserve type (Ⅰ ), high pressure-high reserve type (Ⅱ) and normal to transitional pressure-high reserve type(Ⅲ). The formation and evolution of paleopressure controlled the formation of gas reservoirs. Successive pressure increase caused by gas generation and compression resulted in superhigh pressure-low reserve type reservoirs (Ⅰ) ; long-term pressure increase resulted in long distance gas migration and trap area enlargement, and thus forming high pressure-high reserve type reservoirs (Ⅱ); the development of structural fractures and high-pressure enlarged fractures, the early-stage enrichment and late-stage reformation of the reservoirs should be the basic formation model of normal to transitional pressure-high reserve type reservoirs(Ⅲ).