Prediction of pore and fracture pressure using well logs in Mishrif reservoir in an Iraqi oilfield

Formation pressure is the most critical parameter in hydrocarbon exploration and exploitation. Specifically, predicting abnormal pressures (high formation pressures) and subnormal pressure zones can provide valuable information to minimize uncertainty for anticipated drilling challenges and risks. This study aims to interpret and delineate the pore and fracture pressure of the Mishrif reservoir in the southern Iraq Oilfield. In addition, the other goal was to investigate the methods of calculating vertical stress. Several methods have been employed in the present work to predict the overburden, pore, and fracture pressure using wells log data. Overburden pressure was estimated using, Wendt-non-acoustic module, Traugott module, Miller module, Amoco module, average density input module, extrapolation module, and Gardner module. In addition, the pore pressure was predicted using Eaton Methods (resistivity approach and sonic velocity approaches), Bower's original, and Bower's sonic methods. In contrast, the fracture pressure was estimated by using only Eaton Methods. The data required to implement this study included deep resistivity, acoustic compression wave, gamma-ray, bulk density, and drilling events. Furthermore, supporting these models needs the pore pressure measurement from Modular Formation Dynamics Tester (MDT). Sixty-six measured values of pore pressure were used to validate the methods as mentioned earlier. Except for the Gardner module, all methods produce an acceptable estimation of the overburden, pore, and fracture pressures. The Miller module presented the more accurate to match the bulk density log. For the pore pressure, the results of sonic velocity approaches like Bowers original and Bower's sonic method are similar. The mean absolute percentage error (MAPE) was about 4% to 6% using sonic velocity approaches, Bowers original, and Bower's sonic method. In comparison, it was about 120% to 150% using the resistivity approach for Eaton's method. Finally, the fracture pressure results were fully consistent with the actual drilling report and drilling events.