An Applied Geomechanics Study of Pore Pressure and Fracture Gradient Model for Well “BEN-1”, Pre-Kujung Formation

Abstract

An exploration well of BEN-1 was drilled to total depth of 1275 m with main target of Pre-Kujung Formation. There were some problems during the drilling, such as caving and lost circulation. The lack of geomechanics study led the creation of a mud program cannot reach the wellbore stability. This paper discusses about the applied geomechanics study to predict pore pressure and fracture gradient model and evaluate the mud program. Wellbore stability can be achieved as the safe mud window follows the common rule of Pore Pressure < Shear Failure Gradient < Mud Weight < Minimum Horizontal Stress < Fracture Gradient < Maximum Horizontal Stress. Analysis results show the pore pressure and fracture gradient model can be predicted using Eaton’s method, minimum horizontal stress using pre-existing failure of Mohr-Coulomb method, maximum horizontal stress with tectonic constant of 0.5 (normal fault), and shear failure gradient using modified Lade criterion. Based on the PPFG model, the stable mud weight recommendations are 10.4 – 11.5 ppg at 0 – 540 m depth (20” casing), 8.33 ppg at 540 – 693 m depth (13⅜” casing) with blind drilling, and 9.6 – 11 ppg at 693 – 1245 m depth (9⅝” casing).