The Design of Stable Foam Fracturing Treatments

Hydraulically induced fractures have been used to stimulate oil and gas wells for the past 25 years. Hassebroek and Waters" summarized the advancements in fracturing technology through the first 15 years. During this period, great strides were made in the understanding, engineering and mechanical aspects of hydraulic fracturing. In the last few years, interest in hydraulic fracturing has gained a renewed momentum. The combination of declining domestic reserves and increased prices for oil and gas has turned the petroleum industry's attention toward the recovery of hydrocarbons from tight reservoirs. In these low-permeability formations, hydraulic fracturing treatments are routinely performed upon initial completion. Successful stimulation depends upon creating a fracture, which can be propped for the desired length, using a fluid that does not substantially reduce the formation permeability next to the fracture. The selection of the fluid, therefore, is usually the key to designing a successful fracture treatment. One of the more recent innovations in fracturing technology is the use of foam as a fracturing fluid.2" Foam, which is a mixture of gaseous nitrogen, water and a surfactant, has been used for many years as a drilling and workover fluid. The properties of foam, such as low hydrostatic head, low water content and excellent suspension of solids, make it an ideal fluid for drilling into or working over low-pressure, water-sensitive reservoirs. These same properties led to the development of foam as a fracturing fluid. The viscosity of foam was investigated by Mitchell.7 His experimental findings confirmed the existing theories that foam flow could be predicted using single-phase flow theory. Blauer, et a1.8 extended Mitchell's work by investigating foam flow in oilfield-size tubulars. The results of their work have been successfully applied to the design of hundreds of stable foam fracturing treatments during the past two years. The properties of foam as a fracturing fluid have been well documented.2"3 In both Refs. 2 and 3, sections were included which discussed the design procedure for fracturing with foam. The purpose of this paper is to present a computerized approach to the engineering design of stable foam fracturing treatments. A computer program, which is available for industry use, has been written which calculates the behavior of the foam in the tubulars and the resulting fracture dimensions. The effects of specific changes in fracture treatment design can be easily analyzed, which allows the engineer to optimize the treatment design.