Study On Pore Pressure Prediction Method Of Compound Salt Layer In Front Of Kuqa Mountain,Tarim

Composite salt layer is widely developed in Tarim Oilfield.It may develop highpressure salt water layer in sand mudstone and limestone above,between or under salt,which brings great challenges to drilling.Because the dense gypsum and salt rock developed in the composite salt layer divide the formation into multiple high-pressure systems,the conventional pore pressure prediction method is not applicable.Pore pressure is mainly interpreted by P-wave velocity.Due to the compactness of the salt gypsum layer itself,the abnormal high pressure laws above,between and under salt are different,resulting in different P-wave velocity responses.In order to establish the pore pressure prediction model of composite salt layer based on logging data(Pwave velocity),this paper analyzes the acoustic logging response of composite salt layer,analyzes the limitations of calculating pore pressure by acoustic logging,and then establishes the P-wave velocity equation of composite salt layer based on the most basic theory of pore elasticity,so as to prove the factors affecting the P-wave velocity of composite salt layer theoretically,so as to provide a basis for predicting pore pressure.Because the composite salt layer is divided into multiple high-pressure systems,the accurate identification of high-pressure salt layer is the basis of pore pressure prediction of composite salt layer.This paper explores the identification of high-pressure brine layer by using traditional methods and clustering methods.Traditionally,the identification of high-pressure salt water layer is obtained by comprehensive analysis of logging and logging data.Although this method can identify high-pressure salt water layer,it seriously depends on the experience of staff and is time-consuming and laborious.Aiming at the problems of traditional methods in identifying high-pressure brine layer,this paper explores the use of Agnes algorithm to identify high-pressure brine layer,and the results show that the prediction accuracy is more than 94%.The key to the research on the abnormal pressure of composite salt layer is the accurate prediction of pore pressure.Starting from the theoretical mechanics of pore elasticity,based on the most basic theoretical mechanics of pore elasticity and the modified Gassmann equation,a new method suitable for the prediction of pore pressure of composite salt layer is established in this paper.Firstly,the longitudinal wave velocity equation of the high-pressure brine layer is established and the main factors affecting the high-pressure brine layer are analyzed.Secondly,the identification method of the high-pressure brine layer is explored.Thirdly,a new method for predicting the pore pressure of the high-pressure brine layer is proposed.