The Evaluation of Proppant Transport and Cleanup of Foamed Fluids Used in Hydraulic Fracturing of Shallow, Water-Sensitive Reservoirs

Abstract

SPE Members Abstract The use of foamed fluids has become popular in coal and shale reservoirs due to their inherent non-damaging properties. Foam is generally considered to be a perfect transport fluid. However, the proppant transport properties have not been fully measured in the laboratory. This paper discusses the design and construction of equipment to generate stabile foams in the laboratory and in the field, as well as the measurement of proppant transport and cleanup of foams commonly pumped into shallow, water sensitive reservoirs. The equipment assembled for measuring proppant transport of foamed fluids includes a high pressure slurry pumping system, a choke system to generate field quality foams, a pipe rheometer to obtain in-line pipe rheology, a high pressure, see-through slot with remote video to observe proppant transport and a pressure control and exhaust system. Other equipment used includes a conventional sand column generator and core flow equipment to look at the impact of foam on coal permeability. Several tests have been completed including the optimization of mixing tube diameter and velocity to achieve a stabile foam in the laboratory and in the field. The impact of gel concentration and surfactant concentration on foam stability is measured to achieve minimum stability and maximum cleanup. Various surfactants are evaluated for cleanup. Their ability to avoid foam regeneration or blockage during flowback is also evaluated. Finally, the rheology, transport properties and half-lives of foams with and without sand are examined. Introduction The primary objective of most hydraulic fracturing treatments is to place proppant within the hydraulically created fracture. A secondary objective is to cleanup the transporting fluid such that the formation regains permeability and the proppant pack retains conductivity. In coalbed methane and shales the two objectives must be at least combined, if not reversed, for the fracturing treatment to be successful. Certainly the proppant must be placed within the zone of interest, but more importantly, a minimum amount of residual damage should remain in the fragile, cleated permeability system. The leakoff of common gelled fracturing fluids through the cleat system of coal has been shown to cause reductions in the coal cleat permeability on the order of 90%. The high damage potential of gelled fluids in coal has led to the use of foamed fluids to place proppant. P. 331^