In the Rangely Field in Colorado, five decades of fracture optimization can be traced. A 1992 update by Hejl showed the results of 198 recent refracture treatments, with current designs specifying pumping rates exceeding 80 bbl/min and 8 to 12 lb/gal sand. Pads have been reduced and FLA eliminated to maximize conductivity. The average incremental production from 85 wells restimulated in 1990 was 52 bopd during the first year, and over 1.66 MMBO incremental from March 1990 to January 1992
This paper presents the methodology used to optimize high rate refracturing treatments in a massive sandstone reservoir and associated incremental production response in a carbon dioxide (CO2) flood. Fracturing at high rates (70 to 100 bbl/min) using 10 lb/gal sand concentrations is necessary to fracture 700 ft of gross interval with 250 ft to 300 ft of net pay from six producing horizons.
Optimization of the work process reduced workover costs, fracturing costs, and contamination of the reservoir by fracturing additives and fluids. After the workover procedure was streamlined, fracture fluid additives and volumes for the pad, ramp, and final sand stage were examined.
It was hypothesized that fracturing in the area of the reservoir flooded with CO2 would accelerate CO2 breakthrough problems, causing increased CO2 production. Refracturing has increased the produced processing rate in the CO2 area of the reservoir, with little or no increase in CO2 gas production. Refracturing bypassed near wellbore damage caused by barium sulfate scale and asphaltene precipitation associated with the CO2 miscible flood. Incremental oil response attributed with refracturing for the full field and CO2 flooded areas since March 1990 has averaged 52 and 58 BOPD, respectively, on a total of 85 wells.
Author(s): Chevron USA Inc., K.A. Hejl
Paper Number: SPE 24346