Wellbore Cooling as a Means To Permanently Increase Fracture Gradient

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn recent years, several techniques have been proposed to increase the fracture gradient by inducing changes in the near wellbore region (Alberty and McLean, 2004;Sweatman, et al., 2004;Benaissa et al., 2005). This process, often called "wellbore strengthening", has most recently been implemented by adding specially designed proppant material to the mud before raising its pressure above the fracture gradient. The goal was to induce short tensile fractures in the vicinity of the wellbore wall which are prevented from propagating; thus, creating a "stress cage". However, this method has often proven ineffective in low permeability formations where mainly uncontrolled fracture propagation occurs.The purpose of this paper is to propose and evaluate the use of wellbore cooling, in combination with more classical stengthening processes, to permanently increase the fracture gradient without the risk of circulation losses inherent in the "stress cage" method, as it is currently applied. This approach involves lowering the temperature of the drilling mud; thus, reducing the hoop stress at the borehole wall and then 'setting' the stress cage in the standard manner. Tensile cracks can then be induced at significant lower mud weights. Given the typical thermal conductivity properties of rocks, the tensile stresses induced by cooling (and consequently, the created fractures) will tend to be confined to the near wellbore region.This work presents an evaluation of the effect cooling has on the stress profile of a "solid" material and compares it with a fully coupled thermoporoelastic solution. The results of such analyses may then be used to design a field application to test this novel idea.