THE QUANTITATIVE CALCULATION OF ABNORMAL FLUID PRESSURE IN ARGILLACEOUS AND ARENACEOUS ROCKS AND ITS GEOLOGICAL APPLICATIONS
Chen Heli;Luo Xiaorong Northwest University, Xi'an
Usually there is abnormal f1uid pressure at a certain depth in continental basins.Its development has a close relationship with the sediments of deep-semideep lacu-strine facies which consist mainly of argillaceous rocks. Now it is believed that the regional abnormal pressure in arenaceous rockschiefly comes from that of the adjacent argillaceous rocks. As different lithologieshave different conditions of formation and maintenance of high pressure, the pressu-res of adjacent argillaceous and arenaceous rocks are not necessarily equal. However,they often vary synchroneouslly, the former being commonly higher than the la-tter. On the basis of mudstone compaction curves, the subsurface fluid pressure canbe calculated. The results obtained with the general equilibrium-depth method aresuitable for argillaceous rocks. But the results obtained with the opposite-deducedequilibrium-depth method and other empirical relation, methods are closer to thepresent pressure of reservoirs. The present pressure and expulsion quantity of mud-stone may be used to analyse the relative distribution of ancient formation press-ure. According to the data of fluid pressures, the depth, time, direction and verticaldistance of Primary hydrocarbon migration from source rocks can be dotermined.Thesti data can also help to predict the direction of second migration of hydrocar-bone and their favourble accumulation zones.