Waterless Stimulation for Unconventional Resources: An Alternative to Conventional Water-Based Fracturing Techniques

Abstract

Abstract Compared with hydraulic fracturing, waterless fracturing can alleviate pressure on water resource significantly. Studies have been made to the LPG waterless fracturing, waterless fracturing with liquid CO2, high-energy gas fracturing and cold fracturing with liquid N2, to identify the feasibility of these technologies with lower operation costs. It is believed that new environment-friendly fracturing technology is expected in the future. Among the existing waterless fracturing technologies, waterless fracturing with liquid CO2 is the most feasible one with safe and efficient performance. CO2 is a kind of ideal fracturing fluid, which is easy to liquefy, safe and non-explosive. CO2 fracturing can efficiently stimulate the reservoir, without damage to the reservoir and with less water consumption. It is qualified for operation in view of energy conservation, emission reduction and environmental protection. This technology is significant for clean and efficient development of low-permeability tight oil reservoirs, and worthy of broad application. CO2 fracturing technology is one of the waterless fracturing technologies. It has the advantages of water free, low reservoir damage, and production increase by improving the reservoir pressure. However, the technology faces the challenges of low viscosity of liquid CO2 and difficulty to pump proppant. No conventional thickening agent can provide the required thickening in 100% liquid CO2. In this paper, the problem of thickening gelled liquid CO2 has been solved by developing a new surfactant and thickening agent. Surfactant additive agents can make the liquid CO2 gel by forming wormlike micelle or cylinder micelle structure. The cylinder micelles enhance the viscosity through entanglement inter-action above a critical concentration. By a high pressure pipeline rheological experimental device, the effective viscosity of liquid CO2 gel fluid is between 7.654 – 20.012mPa.s, and the viscosity of liquid CO2 increases by 95 to 498 times under the same conditions. The new liquid CO2 based gel fracturing fluid has been used in five wells of Jilin Oilfield in China, during the fracturing, 19.8 m3 of proppant was successfully pumped to the reservoir in one well, at a mean proppant concentration of 6.8%, as a result, the production of them has increased by over 100%. With low viscosity and high diffusion coefficient, supercritical CO2 is good for improving fracturing volume. Effective CO2 fracturing technology can improve stimulated reservoir volume, downhole monitoring results show that the cracks formed by CO2 fracturing is 2.6 times the size of those formed by water-based fracturing.