Development of a pore pressure and fracture pressure gradient prediction model for few exploration blocks in Mannar and Cauvery basins, offshore Sri Lanka

Abstract

Availability of a pore pressure and fracture pressure gradient prediction model for petroleum well drilling is a basis for safety, cost effectiveness and the efficiency of the overall drilling program. Petrophysical data and measured pressure data of four wells previously drilled in the Mannar basin and Cauvery basin were reviewed to establish such a model for few petroleum exploration blocks in Sri Lanka. The pore pressure gradient prediction strategies used for the analysis are, Hottman and Johnson method, Ben Eaton method and D-exponent method. Hubbert and Willis method, Ben Eaton method and Matthews and Kelly method are the fracture pressure gradient prediction strategies used. Area specific variables including Poisson ratio and matrix stress coefficient were determined prior to fracture pressure gradient prediction. After a statistical analysis and comparison with well log data, a combination of Hottman and Johnson method and D-exponent (Eaton) method was selected as the best suited pore pressure gradient prediction model for the drilling area. The analysis of fracture pressure gradient strategies found that the Ben Eaton method is the best suited method for the area. After determining the suitable prediction methods, the Petrel software was used to visually interpret and analyze the results obtained. The research findings will help for future drilling operations and well planning in the specified area in Mannar and Cauvery basins.