Origin And Evolution Characteristics Of Overpressure In The Xiaganchaigou Formation In The Yingxi Area And Its Controlling Effect On Reservoir

Overpressure is popular in Yingxi area,and the study overpressure is the key to evaluating the control effect of overpressure on oil and gas reservoirs in this area.In order to clarify the formation mechanism and evolution characteristics of overpressure and its controlling effect on the oil and gas reservoirs of the Xiaganchaigou Formation,this paper analyzes the current characteristics of overpressure in the study area based on the measured pressure data from drilling in the Yingxi area.On this basis,combined with the comprehensive compaction curve characteristics of typical drilling mudstones in Yingxi area,deposition rates of different periods,hydrocarbon generation potential of organic matter,identification chart of overpressure genetic mechanism,and the determination of rock paleostress by acoustic emission method of samples in the study area,the formation mechanism of overpressure in the study area was analyzed.By analyzing the evolution characteristics of formation overpressure in the Xiaganchaigou Formation in Yingxi area,the influence of formation overpressure on hydrocarbon accumulation is analyzed.The results show that:(1)Overpressure is common in the Xiaganchaigou Formation in Yingxi area,and the overpressure increases gradually with the increase of depth.(2)The formation of overpressure in the study area is the result of the combined action of many factors.The main mechanisms of overpressure are uneven compaction,hydrocarbon generation pressurization,overpressure transmission and horizontal tectonic compression.(3)According to the numerical simulation of fluid overpressure,the evolution of formation pressure is divided into 4 stages.The first stage is about 23.5Ma before,and the target layer has weak overpressure due to uneven compaction;the second stage is about 23.5～Between 11.5Ma,the source rocks began to generate hydrocarbons,and the hydrocarbon generation had a continuous contribution to the evolution of overpressure,and the formation pressure increased slowly at this stage;in the third stage,between 11.5～7Ma,during the depositional and horizontal tectonic compression Under the combined action,the overall pressure of various formations increases rapidly,especially for the mudstone formations rich in organic matter.In addition,the hydrocarbon generation pressurization makes the formation pressure increase more rapidly.The development of overpressure fractures and faults makes the source rock or mudstone produce overpressure transmission to the adjacent reservoirs,and the pressure of the adjacent reservoirs increases;the fourth stage is about 7Ma to the present,the structural uplift stage,the formation pressure has a small amplitude decreased,but the pressure coefficient increased slightly or remained unchanged.(4)The control effect of overpressure on oil and gas reservoirs in the study area is mainly manifested in three aspects:①The formation of overpressure in source rocks can provide expulsion force for the oil and gas generated in it,and drive oil and gas to migrate to the crystals of adjacent reservoirs.reservoirs in inter-pores and fractures.②The excess pressure difference of the vertical upper source reservoir is the oil and gas charging driving force of different source-reservoir configuration relationships in the target layer in the study area.③The cap rock in the study area is mainly mudstone and gypsum salt rock with high plasticity.The comprehensive sealing effect of cap rock physical properties and overpressure maintains the sealing of oil and gas reservoirs.The good sealing ability of cap rock is the guarantee condition for the preservation of oil and gas reservoirs in the study area.