George T. Woo

A new gelling system for acid fracturing

Typically, the gelling agents used in crosslinked hydrochloric acid are available as polymer dispersions with a pre-blended inverting agent or gellant activator. An inverting agent increases the polymer dispersions viscosity initially and will further increase the polymer dispersions viscosity over the shelf life of the product. As a result, the polymer dispersions pour point and stability are adversely affected, thereby reducing the polymer dispersions shelf life. Additionally, the use of a nonylphenol ethoxylate, the inverting agent commonly pre-blended in polymer dispersions. has been banned in the North Sea due to environmental concerns. A new gelling system for crosslinked acid fracturing treatment has been developed. The system includes a microemulsion polymer gelling agent and a highly specific surfactant that is used as an external activator. The microemulsion polymer possesses very unique and more desirable properties such as a lower pour point and viscosity profile, a greatly enhanced dispersability, and a microscopic emulsion polymer particle. With a lower pour point and innate viscosity profile, the gelling agent is readily pumped directly from the shipping vessels to the blending unit even in cold weather. With such a greatly enhanced dispersability, the gelling agent is readily dispersed in the hydrochloric acid without the risk of forming unhydrated masses or fish eyes. Additionally, the microscopic emulsion particle greatly prolongs the shelf life of the gelling agent by virtually eliminating polymer settling. With the use of the special external gellant activator, the emulsion polymer could achieve 70% or more hydration within one minute. The characteristics of the gelling agent and the use of the external activator enable the gelling system capable of continuous mix or on the fly gelling operations. In addition, this external activator is biodegradable making it more conducive to environmental concerns. This paper describes the chemistry of the new gelling system, its enhanced gelling capabilities, discusses the results of lab testing leading to its development, and finally, the results of extensive field-testing.