Discussion on a Formation Pore Pressure Detection Method for Carbonate Rocks Based on the Thin Plate Theory

The current formation pore pressure detection methods for carbonate rock have shortcomings.In order to ensure drilling safety of carbonate rock in the F formation,Y Oilfield,the formation pore pressure detection method was studied.The geo-mechanical model of formation pore pressure was proposed under tectonic compression,based on the thin plate theory,considering the effect of bulk modulus and in accordance with carbonate rock characteristics.Based on the analysis of the geological structure,abnormal over-pressure and logging response of carbonate rock in F formation,combined with exclusive method,the generation mechanism of abnormal over-pressure was studied.When a formation pore pressure detection method was applied to F formation,Y Oilfield,the study showed that the minor faults were developed and the P-wave velocity is about 5 500 m/s in F formation.Formation pore pressure coefficient of FU formation and FL formation was about 1.45 and 1.30 respectively.The deformation of rock framework of FU formation was larger than that of FL formation,and the main generation mechanism of abnormal over-pressure was based on tectonic compression.The application results showed that the error of formation pore pressure detected value was less than 10% when compared with SFT measured value.Formation pore pressure increased with the increase of tectonic deformation curvature,formation pore pressure coefficient and elasticity modulus,and decreased with the increase of Poisson’s ratio,which was shown in the linear relationship.The study suggests that formation pore pressure detection method of carbonate rock based on the thin plate theory could be used to detect pore pressure of carbonate rock caused by tectonic compression.