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.

Wellbore Cool Down During Hydraulic Fracturing Simplifies Using Dissolvable Materials

“…An often over looked aspect of pumping fluids into a well bore, such as during hydraulic fracturing, is that the injected fluids will significantly reduce the temperature of the well bore. The cooling effect of circulating mud during drilling has been measured and numerically modelled [5] and has implications for borehole stability [6]. During acid stimulation, distributed fiber-optic measurements have demonstrated the cooling effect of the injected fluid [7] and have used this distributed measurement to determine where the acid is entering the formation [8,9].…”

Parametric Analysis of MPD Hydraulics

“…A simple means of determining this pressure jump due to YP is given by equation 2 7 dP/dL = YP/[200(d 2 -d 1 )]…………………………. (2) This pressure drop represents the last increment of choke pressure that must be imposed prior to shutting the rig pumps completely off the hole before making a connection and represents the first increment of choke pressure that must be bled off the annulus when the rig pumps are put back on the hole after making the connection. Any accurate hydraulics model can be used to calculate the friction pressure represented by any given increment of circulation rate.…”