Pressure distribution characteristics and overpressure genesis of the Permian formation in Mahu Sag and surrounding areas
Recent drilling examples have revealed the widespread existence of overpressure in the Permian clastic rock layers of the Mahu Sag,but the distribution of overpressure remains unclear and the research on the main controlling factors of overpressure are relatively weak.This paper aims to analyze the vertical and horizontal distribution patterns of abnormal pressure in the Permian of the Mahu Sag,clarify the main controlling factors of abnormal pressure,elaborate the formation mechanism of overpressure,and reveal the relationship between overpressure and oil and gas distribution.Using 79 measured pressure data from 65 wells,drilling mud density and well logging curve data,this study employed well logging curve analysis,Bowers method,and density-acoustic velocity crossplot method to predict pressure using the equilibrium depth method and Eaton method.Based on these predictions,the main reasons for the formation of overpressure were comprehensively discussed in combination with the geological environment of overpressure development.Abnormal pressure in the Mahu Sag exists in the Triassic Baijiantan Formation and underlying strata,with gradually increasing pressure in the lower strata and a single structural characteristic vertically.The abnormal pressure in the Lower Wuerhe Formation gradually increases from the Wuxia Fault Zone to the southeast direction,reaching a maximum pressure coefficient of 2.0 in the Dabasong Bulge.The hydrocarbon generation and pressure increase effect of source rocks is an important factor in the formation of overpressure in the Mahu Sag.The Lower Wuerhe Formation in the Manan slope and the Upper Wuerhe Formation in the Zhongguai Bulge are caused by a combination of unbalanced compaction and hydrocarbon generation pressure increase,while the Fengcheng Formation is caused by a combination of tectonic compression and hydrocarbon generation pressure increase.The Lower Wuerhe Formation in the Dabasong Bulge is caused by fluid expansion and pressure conduction.Due to the development of faults in the western slope area of the Mahu Sag,the overpressure caused by tectonic compression has dissipated,leaving only the overpressure response characteristics of the logging curve formed by tectonic compression.The current overpressure is still dominated by hydrocarbon generation pressure increase,which provides the power for oil and gas migration.Faults generated by tectonic activities serve as pathways for oil and gas migration and pressure conduction,affecting the magnitude of abnormal pressure and the vertical distribution of oil and gas in the area.
Mahu SagPermian strataFormation pressure distributionGenesis of overpressurePressure prediction
万方数据
维普
