Increasing Effective Fracture Gradients by Managing Wellbore Temperatures

Abstract

Abstract Thermal effects on wellbore stresses can have a significant impact on effective fracture gradients. Changes in wellbore temperatures caused by various drilling operations provide for these thermal effects. For example, circulation on bottom usually results in lower bottom hole temperatures than the static geothermal temperature. This cooling effect reduces the wellbore stresses resulting in lower effective fracture gradients. Minimizing the cooling effect by increasing wellbore temperatures can increase effective fracture gradients and the corresponding pore pressure/fracture gradient margin avoiding costly lost circulation and additional unnecessary casing points. This paper presents results from leak-off tests taken at various temperatures which demonstrate the thermal effect on formation stress. This paper also examines the effects of operational factors on wellbore temperatures to minimize the cooling effect and/or increase effective fracture gradients. Software developed for thermal simulation of various drilling operations was used to perform the analysis.