Seal Mechanisms Of Mudstone Caprocks To Gas In Each Phase And Their Quantitative Research

Based on the study of migration mechanisms of gas in different phases, the seal mechanisms of mudstone caprocks to gas in each phase were overally and systemly studied. Capillary seal was considered to be the main seal mechanism of mudstone caprocks to gas in free phase. Abnormal pore fluid pressure can play an in direct role in sealing gas in free phase, Absorption was considered to be the main seal mechanisms of mudstone caprocks to gas in water-soluble phase. Abnormal pore fluid pressure can also play an important role in sealing gas in water-soluble phase. Restraining and replacing concentration seal was considered to be the main seal mechanisms of mudstone caprocks to gas in diffusion phase. By displacement pressure, abnormal pore flow pressure, absorption force, abnormal gas-bearing concentration and generation gas intensity. The seal ability of mudstone caprock to gas in each phase was overly and systemly studied. Displacement pressure was basic parameter evaluating the capillary seal ability of mudstone caprocks, it can be gotten by experiment, and be gotten by the data of interval transit-time and seismic velocity in the basic of experiment. Abnormal pore fluid pressure is an important factor influencing seal ability of mudstone caprock to gas in free phase. It can be gotten by the data of interval transit-time or by the data of seismic velocity. Abnormal gas-bearing concentration was considered to be the main parameter evaluating the restraining concentration seal ability of mudstone caprocks, it can be gotten by the conditions of temperature and pressure. Gas-expulsion intensity can reflect the hydrocarbon generation characteristics of mudstone caprocks, it can be used as a parameter evaluating the replacing concentration seal ability of mudstone caprock, it can be gotten by the research results of generation hydrocarbon of gas source rocks. Compaction diagenesis stages can reflect the seal ability of mudstone caprock to gas in water-soluble phase, it can be gotten by the research results of diagenesis of mudstone. From structure and structural evolution, sedimentary environment and compaction diagenesis. The favorable formation conditions of mudstone caprock was discussed. The sags of basin were considered to be the most favorable areas of formation and development of mudstone caprocks. The maximum water invasion period of relatively submerged with a great scale in a basin was considered to be the most favorable period of formation and development of mudstone caprocks. Shallow-sea facies, semideep lacustrine and deep lacustrine facies and broad tidal flat and lagoon facies were considered to be the most favorable sedimentary environments of formation and development of mudstone caprocks. A swbage of late diagenesis was considered to be the strongest stage of seal ability of mudstone caprocks. Based on the study of seal mechanism of mudstone caprock to gas in each phase and formation conditions, the evolution and evolution stage of seal ability of seal ability of mudstone caprock was studied. Capillary seal is generally the seal mechanism to gas in free phase, As soon as mudstone caprocks deposited, their seals to gas were formed. With the increase of depth, the capillary seal ability of mudstone caprocks increases. Abnormal pore fluid pressure can only exist in uncompacted mudstone caprocks, and in special stage of their diagenesis evolution.Restraining concentration seal and replacing concentration seal can only exist in the mudstone caprocks with generation hydrocarbon ability. As abnormal pore fluid pressure, restraining concentration seal can only exist in the special stage of their diagenesis evolution. Replacing concentration seal of mudstone caprocks formed when they began to generate gas. With the increase of evolution degree of organic matter, the replacing concentration seal ability increases. Utilizing the functional relation between displace and depth, the functional relation between abnormal pore fluid pressure and interval transit-time and the functional relation among abnormal gas-bearing concentration and temperature, pressure, the recovering methods of ancient displacement pressure, ancient abnormal pore fluid pressure and ancient abnormal gas-bearing concentration was established. Using the corrected Darcy's law, based on the comprehension of development characteristics and seal ability, a method evaluating comprehensively and quantitatively the seal ability of mudstone caprocks to gas in free phase and gas in water-soluble phase was established through defining and calculationg CSFI and CSWI indexes. Using the corrected Fick's law, based on the comprehension of development characteristics and seal ability,a method evaluating comprehensively and quantitatively the seal ability of mudstone caprocks to gas in diffusion phase was established through defining and calculationg CSDI index. From the matching relation of time and apace between mudstone caprock and sourcerock, the role of mudstone caprock in gas accumulation and distribution was deeply studied. The space distribution matching relation between caprock and sourcerock controls the distribution and accumulation of gas. The space quality matching relation between caprock and sourcerock controls the accumulation places of gas. The time matching relation between caprock and sourcerock controls the accumulation and preservation amount of gas. The space development places of caprocks controls the formation of different types of traps.