Gas Well Stimulation with a Viscous Water-Base Fracturing Fluid

Abstract

Field experience with high-viscosity fracturing fluids shows that they are highly effective, particularly in stimulating wells with bottom-hole temperatures of 200 degrees to 400 degrees F. The propped-fracture length and fracture conductivity are greater than with low-viscosity fluids; consequently, productivity is greater. Also, abandonment pressures can be lowered, which means additional reserves. Introduction A viscous, water-base, non-Newtonian fracturing fluid has been used successfully to stimulate seven Wilcox (Upper Eocene) and two Vicksburg (Lower Oligocene) gas wells. The bottom-hole temperatures of the completions ranged from 240 degrees to 330 degrees F. The average gas production increase was 2.8 MMcf/D, compared with 0.7 MMcf/D for treatments performed on similar wells treated with low-viscosity performed on similar wells treated with low-viscosity fluids. The principal application of this high-viscosity fluid is in the stimulation of reservoirs with bottom-hole temperatures ranging from 200 degrees to 400 degrees F. Use of the fluid results in wider fractures, placement of proppant at higher concentrations, and better proppant distribution than is achieved with low-viscosity fluids. The improvement in response has been attributed to greater fracture conductivity and greater propped-fracture length. Treatment Results The total daily production of nine wells treated with the viscous fluid was increased from 16.6 to 40.6 MMcf, with the average Q/Qo being 3.2. (Q/Qo is the ratio of production rates after fracturing to production rates before treating.) In determining Q/Qo, increased tubing pressure and tubular friction were neglected. Depths of the completion intervals ranged from 8,000 to 12,000 ft. All of the treatments were performed on wells that were greater than 50 percent pressure depleted. Calculated closure stresses on the propped fractures ranged from 5,000 to 9,000 psi. Other pertinent well and treatment data are given in Table 1. pertinent well and treatment data are given in Table 1. Stimulation results previously obtained on comparable completions using low-viscosity fluids had been discouraging. Data on five such treatments performed on Wilcox gas wells are presented in Table 2. In the table below the average well data and results of these stimulations are compared with results of seven treatments on Wilcox completions using the viscous fluid. High-Viscosity Low-ViscosityFluid (7 wells) Fluids (5 wells) Net pay, ft 49 38 Bottom-holePressure, psi 1,390 1,550 Original bottom-holepressure, psi 3,900 3,900 Average productionincrease, MMcf/D 2.8 0.7 Average Q/Qo 3.6 2.2 Profitable operations 7 2 Profitable operations 7 2 Uneconomicaloperations 0 3 Stimulation treatments using the high-viscosity fluid have yielded greater response under similar well conditions than have treatments with low-viscosity fluids. Improved stimulation response is attributed to longer propped fractures and higher fracture conductivity than could be obtained with low-viscosity fluids. JPT P. 1385