A Novel Nano-Composite Fiber Laden Viscoelastic Fracturing Fluid for Coal-Bed Methane (CBM) Reservoir Stimulation: Laboratory Study and Test

Due to strong adsorption characteristic and extremely developed natural fracture system in coal, improper choice of fracturing fluid will result in two major problems: one is damage to the coal formation and hydraulic fracture; another is the ineffectiveness in hydraulic fracture creation and propagation. With the merits of small damage and easy flowing back, viscoelastic surfactant(VES) fracturing fluid is becoming a preferred option. A high surfactant concentration may be necessary to enhance the proppant-carrying capacity, but as a tradeoff, it has a bigger potential to increase the absorption loss in the seam and create barriers to rod micelle breaking in low temperature condition. By introducing nanoparticles in the conventional polyester fiber, a new kind of nano-composite fiber which has obtained major improvements in functional and structural properties was synthetized. A novel Nano-composite Fiber Laden VES(NFVES) fracturing fluid was developed. A series of evaluation tests were performed in laboratory. The results shown this fiber can disperse easily in the fluid and an addition of small amount(0.5%) can enhance the proppant-carrying capacity drastically. To achieve the equal proppant-carrying capacity, the surfactant concentration can be decreased from 2.5% to 1%, which not only reduces costs but also lowers the adsorption of the surfactant in the seam and rock surfaces greatly. The rod micelles can be broken easier at the same time. Friction can be cut by 20% via adding 0.7% nano-composite fiber under the shear rate of 5000s-1. Meanwhile, nano-composite fiber can prevent backflow of proppant effectively. Leak-off of fluid and aggregation of coal scraps can also be mitigated significantly. Continuous degradation of the fiber takes place with the passage of time under the formation temperature, thus reducing the potential damage to the coal seam. The excellent performance of the NFVES fracturing fluid in the laboratory evaluation enjoys great potential and vast development prospects in CBM stimulation.