Genetic Analysis And Prediction Method Of Formation Pressure In Ledong Block Considering Diapir Structure

Under the influence of diapir structure,the distribution characteristics of formation pressure in Yinggehai basin are complex.The mechanism of formation overpressure in Ledong slope zone,which is located in the diapir spread area,is not clear,resulting in a large error in the prediction of formation pressure in this area.In the process of drilling,inaccurate prediction of formation pressure is easy to cause gas invasion and even blowout accidents,affecting safe and efficient drilling.Therefore,combined with the characteristics of diapir structure in Ledong slope zone,this paper studies the genetic mechanism of regional overpressure,the accurate prediction method of formation pressure and its distribution law.Based on the geological background and source reservoir cap rock combination characteristics of Ledong slope zone,the formation mechanism of regional diapir and its influence form on overpressure are analyzed.It is considered that micro fractures are the vertical transmission channel of regional formation pressure.The genetic mechanism of abnormal high pressure in the slope area is analyzed by using the logging method.The results show that the Yinggehai formation is a loading type cause dominated by under compaction,the first member of Huangliu formation is a composite cause dominated by fluid expansion,and the second member of Huangliu formation and below are unloading causes of pressure transmission.Based on the analysis results of overpressure causes,an accurate prediction model of formation pressure is established for non-uncompacted strata.For the first member of Huangliu formation dominated by fluid expansion,a modified Bowers method considering shale content is established.Considering the relationship between effective stress and acoustic velocity,porosity and shale content,a multivariable nonparametric prediction model based on machine learning is established for overpressure formation with the main cause of overpressure transmission.The prediction accuracy of the two formation pressure prediction models in the corresponding formation is more than 95%.Based on the Sequential Gaussian Simulation(SGS)interpolation method,the three-dimensional visualization model of formation pressure in Ledong slope zone is established by using petrel software,and its vertical and horizontal distribution law is analyzed.The results show that the formation pressure increases with the increase of formation depth.However,the vertical distribution characteristics are complex,and there are obvious differences between different horizons due to the influence of pressure transmission.Laterally,with the increase of depth,the formation pressure in the slope area increases gradually from northeast to southwest.The closer it is to the central diapir belt,the greater the influence of diapir and the higher the corresponding formation pressure.