Formation Mechanism And Evolution Characteristics Of The Lower Anomalous High Pressure In The Southern Margin Of The Junggar Basin

The formation mechanism of the abnormal high pressure in foreland basin is complex.In addition to the sedimentary overpressure and the possible transfer overpressure,there are also tectonic extrusion overpressure.In this paper,the sedimentary overpressure,the transfer overpressure and the tectonic extrusion overpressure are comprehensively considered,and the quantitative evaluation and evolution characteristics of the lower assemblage strata in the southern margin of Junggar Basin are summarized.The research results have indirect guiding effect on oil and gas exploration in foreland basin.Therefore,this paper has important theoretical significance and application value.Based on the measured pressure data and the compaction curve of mudstone,this paper analyzes the distribution characteristics of abnormal formation pressure in the study area.By analyzing the compaction curve of mudstone,the history of tectonic evolution and the identification chart of overpressure,the formation mechanism of overpressure in the lower combination reservoir in the study area is clarified.Then,based on the numerical simulation software and relevant calculation methods,the overpressure and evolution characteristics of the two mechanisms of tectonic extrusion and sedimentation are summarized.Overpressure transfer is mainly obtained by comprehensive analysis and correlation of numerical simulation results,measured formation pressure and geological evolution.Finally,in order to quantitatively characterize the evolution characteristics of the overpressure mechanisms in the study area,the supercharging amounts obtained from the above mechanisms are coupled in time and space.The overpressure intensity in the lower Jurassic reservoirs in the study area is entirety weak in the south and strong in the north.In the vertical direction,the excess pressure and pressure coefficient of most anticlinal structures are very different,which are different pressure systems.The mechanism of formation overpressure mainly includes undercompaction,tectonic extrusion and overpressure transfer.The overpressure source of overpressure transfer supercharging is the overpressure caused by the hydrocarbon generation supercharging in the source rock stratum.The weak overpressure of the first row of tectonic belt in the geological history period is mainly formed by undercompaction and tectonic extrusion,and the overpressure transfer basically does not produce weak overpressure.The undercompaction and tectonic extrusion in the second and third rows of structural belts and the eastern part of the four trees depression are the main genetic mechanisms for the formation of strong overpressure,accounting for 50%and 30%of the excess pressure respectively.The overpressure generated by the overpressure transfer is small,mostly around 10MPa,and the proportion of the excess pressure is quite different.On the whole,the relatively large deposition rate since the Cenozoic era led to the emergence of undercompaction in the study area,which resulted in abnormal high pressure.At the beginning of the neogene Himalayan Movement,the northern tianshan mountain was rapidly uplifted and the most intense compressive effect occurred,forming a higher tectonic compressive pressure.Since the beginning of the Neogene system,the Himalayan Movement caused the rapid uplift of the northern tianshan mountains and happened the most intense compression,the study area is formed the high tectonic compressive pressure.From the late sedimentary period of N₁t formation to the early sedimentary period of N₂d formation,the study area began to form a trap,and the overpressure was transferred through channels such as faults to form overpressure transfer supercharging.From the end of the neogene to the quaternary period,the uplift and denudation of strata gradually reduced the overpressure and only weak overpressure and close to normal pressure were finally preserved in some areas,the continuous settlement in most areas increases the overpressure to a certain extent,but the increase is relatively small.