Fiber Assisted Enhanced CO2 Foam Fracturing and Proppant Placement

Abstract

Low-pH fracturing fluid systems face a challenge to maintain rheological stability at elevated temperatures beyond 300°F. The objective is to have a reliable fluid system with high foam quality and viscosity demonstrating required proppant transport and retained permeability at the end of the treatment. To best balance the tradeoff, a solution that has been utilized for many treatments is to viscosify a novel biopolymer-based slurry gel fluid system with CO2. There are associated challenges with this strategy, though, in generating sufficient fracture width to place higher proppant concentrations. In this paper, we summarize a case study where enhancement of foam stability utilizing degradable fiber showed some improvement in proppant placement performance. Degradable polymer fiber with novel polymer rearrangement was utilized to enhance the performance stability and used with the base fluid. Foam half-life was measured by varying fiber concentrations from 0 to 32 lbm/1000 galUS. Static and dynamic proppant transport was also studied by varying fiber concentrations from 0 to 22 lbm/1000 galUS. Proppant utilized for this testing was high-strength ceramic proppant. After the laboratory phase, fracturing treatment was implemented in two wells with CO2-assisted foam fracturing with (Well-B) and without the fibers (Well-A) to analyze the impact on proppant placement. Three different fiber products made of different synthetic polymers were utilized in the initial phase to compare for proppant settling, and the high-temperature (HT) version was selected based on superior proppant suspension at high temperatures. For the next evaluation phase, the addition of HT fibers increased the foam half-life from 100 minutes to 200 minutes for 0 and 32 lbm/1000 galUS loadings, respectively. Similarly, the proppant settling time was increased from 59 minutes to 152 minutes for 0 and 15 lbm/1000 galUS loadings, respectively. Slot tests were conducted in a 3-mm slot to evaluate proppant transport in dynamic conditions and showed no sand banking effect with fibers. Tests were conducted with 0, 8, and 22 lbm/1000 galUS of fibers and show a clear impact of the fiber addition. During the field implementation, the HT fiber addition of 20 lbm/1000 galUS demonstrated 15% lower friction analyzed from treating pressure trends at the end of treatment. Also, no indications of near-wellbore bridging, or entry issues were observed in Well-B, similar to Well-A where CO2 foam was pumped without fibers. The implementation of this approach can be impactful for CO2 foam treatments and can also be easily extended to liquid CO2 or supercritical CO2 fracturing, which provides the worst case environment for friction and proppant transport.