Challenges and Uncertainties of Pore Pressure Predictions in Onshore and Offshore Exploratory Wells - A Case Study

Abstract

Geopressure modelling and wellbore stability analysis are of upmost concern, and a key task when designing exploration wells in the Saudi Arabian Red Sea region. Initial modelling is based on seismic, offset wells logs, drilling parameters, lithological distribution and geological history in the area. This paper presents case studies from two wells drilled in Red Sea region, where formation pressures encountered ranged from 75pcf to 140pcf. In the first example, while drilling 16” with 78 pcf mud weight, a kick was taken at 6500ft. Based on cuttings the lithology was reported as 100% halite. During well control operations, a sample was collected and described as 100% shale. Formation pressure was calculated to be 94 pcf, so the well was controlled with 104 pcf. In the second case, a water influx was encountered at base salt which is currently reported as the most intense kick in the area. These events required re-calibration of mud weight calculations and new equations to be applied that take into account the creep of halite in response to temperature. In addition, extreme overpressure and fracture gradients encountered within shale inclusion in salt required a real-time re-assessment of the casing design and casing shoe integrity.