Pilot-Scale Evaluation of Natural-Gas-Based Foam at High Pressures, Temperatures

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201611, “A Pilot-Scale Evaluation of Natural-Gas-Based Foam at Elevated Pressure and Temperature Conditions,” by Griffin Beck, Swanand Bhagwat, and Carolyn Day, Southwest Research Institute, et al., prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5–7 October. The paper has not been peer reviewed. The complete paper presents recent results from a rigorous pilot-scale demonstration of natural-gas (NG) foam over a range of operating scenarios relevant to surface and bottomhole conditions with a variety of base-fluid mixtures. The NG foams explored in these investigations exhibited typical shear-thinning behavior observed in rheological studies of nitrogen- (N2) and carbon-dioxide- (CO2) based foams. The measured viscosity and observed stability indicate that NG foams are well-suited for fracturing applications. Test Facilities Two test facilities were used to explore properties of NG foams at a variety of relevant operating conditions to determine whether NG foam is a suitable alternative to typical water-based fracturing fluids. Pilot-Scale Foam-Test Facility. The pilot-scale foam-test facility (PFTF) is a single-pass pilot plant used to generate and characterize foams at conditions relevant to surface and reservoir conditions. The facility is capable of generating aqueous and oil-based foams using a variety of gases for the internal phase [e.g., methane (CH4), N2, and CO2]. Foams can be characterized at pressures up to 7,500 psi and temperatures up to 300°F. A key benefit of the PFTF is that it can be used to demonstrate new or challenging foaming processes before large-scale or field demonstrations. Further, these processes can be evaluated at conditions relevant to the final application. The test facility consists of three subsystems: a base-fluid system to pressurize and heat the liquid/viscosifier/surfactant mixture, a gas system to pressurize and heat the liquefied gas stream, and the foam test sections to measure various fluid properties of the NG foam. Laboratory Foam-Test Facility. Tests performed on the PFTF were limited to foams generated with pure CH4 and tap water. Additional laboratory tests were conducted to investigate the effects of multiconstituent natural gas mixtures and produced water on foam stability. For these tests, the aqueous base fluid for the foam half-life and foam rheology experiments was prepared from either de-ionized water, tap water, or a synthetic produced water based on a water sample from the Permian Basin. Foam fracturing fluids also typically contain a gelling agent and a foaming agent. The gel was prepared by slow addition of guar to a stirred water sample followed by 30 minutes of mixing to ensure complete hydration. The foaming agent was added and stirred in gently. Three foaming agents were used in this study: anionic Foamer A, nonionic Foamer B, and zwitterionic Foamer C.