| According to the geological,geophysical,and experimental data,based on the accurate prediction of fluid pressure,the types of pressure structure,the formation mechanism of pressure structure,and the indication of pressure structure on hydrocarbon migration and accumulation were studied.The results indicated that overpressure was developed in the Bonan Sag,three overpressure systems developed in Es1,Es3 and Es4 formations.According to the superimposed relationship and the relative intensity of different overpressure systems,pressure structure could be divided into double-bottom-overpressure,tri-middle-overpressure and tri-bottom-overpressure structures.The top boundary characteristics of pressure file was different in different overpressure systems,and could be divided into gradual type and abrupt type.The morphology of pressure body was variable,including funnel-shape,hill-shape,complex funnel-shape,bell-shape and other shapes.By comprehensive consideration of the number of overpressure systems vertically and the characteristics of pressure transition zone,the pressure structure of Bonan Sag could be divided into bottom-gradual double-overpressure structure,bottom-abrupt tri-overpressure structure and bottom-gradual tri-overpressure structure.The formation mechanism of pressure was complex,and was closed related to undercompaction,hydrocarbon generation,seal properties,fluid release,and burial evolution.According to the overpressure formation mechanisms and lithology configuration in the studied area,four types of pressure structure evolution model for thick mudstone and sand-mud interbed under the control of undercompaction,hydrocarbon generation,and the combination of the both were established.The main control factors for the formation of pressure structure were different in different formations.Es1 overpressure systems developed thick mudstone,and the morphology of pressure body was influenced by compaction degree.Es1 was in the early stages of evolution,and overpressure file was mainly funnel-shaped.Es3 overpressure systems also developed thick mudstone,the pressure body was in the later stages of evolution,and overpressure file was mainly hill-shaped,which was influenced by characteristics of hydrocarbon generation and expulsion.Es4 overpressure systems developed sand-mud interbed lithology,was the result of sealing by the top gypsum formation,and overpressure file were complex funnel-shaped and hill-shaped.The distribution of overpressure fracture was different in different pressure types,which was an indicator for hydrocarbon migration in the studied area.For Es4 with abrupt overpressure file,fracture was relatively infrequent in gypsum formation,hydrocarbon mainly occurred migrate and accumulate under the seal.For Es4 with gradual overpressure file,fracture was frequent in the seal,which promoted the vertical migration within the seal,and mainly accumulated in the low pressure reservoir zone between Es3 and Es4.The overpressure file was gradual in Es3,in which fracture distributed widely,and hydrocarbon mainly accumulated in the reservoir within or at the top of the seal.While Es1 developed abrupt pressure body,hydrocarbon could not break through the seal,and mainly accumulated in the reservoir at the bottom of overpressure system.Combined with the types of pressure structure and distribution characteristics of hydrocarbon,the hydrocarbon migration-accumulation pattern under the control of different pressure structures was established. |
PDF Full Text Request