Pore Pressure Prediction and Its Relationship with Rock Strength Parameters and Weight on Bit in Carbonate Reservoirs (A Case Study, South Pars Gas Field)

Abstract

Accurate pore pressure knowledge is particularly critical in drilling, such as drilling safety (avoidance of blowouts and well control lost-time incidents). Pore pressure prediction in carbonate reservoir due to the fact that the pore system and fractures are more complex than the clastic reservoir, also the effectiveness of pore pressure on drilling parameters like weight on bit that has direct effects on drilling rate is very important. As well as, the pore pressure and rock strength parameters have a special place in geomechanical studies. In this study, pore pressure was calculated using the porosity and effective stress in the carbonate reservoir. The porosity was calculated with three methods: neutron–density, neutron–sonic and sonic. The rock strength parameters (Bulk and Shear modulus) were calculated using P and S waves obtained from dipole shear sonic imager log. The calculated pore pressure was compared with modular formation dynamics tester (MDT), WOB and rock strength parameters. The result of the study showed that among available methods, predicted pore pressure with sonic porosity has the best matched to MDT data. Moreover, pore pressure has an inverse relationship to WOB and rock strength parameters, so that with increasing pore pressure of both WOB and rock strength parameters were decreasing. The comparison among predicted pore pressure, mud weight and MDT data was showing that the predicted pore pressure has high accuracy and can use it for geomechanical studies and having a safe drilling operation.