异常高压、流体压裂与油气运移(下)

ABNORMAL PRESSURE,FLUID FRACTURING,AND MIGRATION OF OIL AND GAS

(三)“壳”的破裂与流体运移上述实例表明,现存异常高压生烃泥岩体中的孔隙流体压力是巨大的,原始的古异常高压还要更大一些(甚至等于地静压力)。但是,古异常高压生烃泥岩体排液的先决条件是异常高压带与静水压力带的“接通”。引起“接通”的途径主要有两个:“壳”被天然水力压裂和“壳”被断层活动所断裂。

Based on the informations obtained from Jiyang,China,Gulf Coast,U.S. A.,Azerbaijan,U.S.S.R.and other petroliferous regions,a mechanism for migration of oil and gas has been proposed in this paper. The focal points of this mechanism are as follows:(1)Mainly owing to the rapid deposition,the water expulsion from organic-rich argillaceous sediments was arrested at its shallow burial depth,resulting in a high water content in it.(2) Around the Hydrocarbon-generating mudstone body with abnormal pressure (HGMBAP),a dense“shell”was formed at the contact surface between sands- tone and mudstone,mainly because of the semipermeable membrance effects. (3)All the evolution processes of organic matters almost proceeded in such a undercompacted mudstone body enveloped in the “shell”,with abnormal pre- ssure and high temperature.(4)when loading on the“shell”was unbalanced the underlying undercompacted mudstone and/or plastic salt body began to arch,thus the least compressive stress (S_3) in the “shell” decreased.The fluid pressure in the undercompacted mudstone increased with increasing depth. The combination of the two factors make the natural fluid fracturing to be occurred in the arched parts of the“shell”.Therefore,the hydrocarbon-bearing fluid migrated from the abnormal pressure zone to hydrostatic pressure zone. Such a process proceeded repetitively and intermittently. According to the above-mentioned mechanism,the author of this paper suggests that oil and gas pools can be formed in any trapped reservoir spaces which communicated with paleo-HGMBAP during geological history.