Recently there has been a push to pursue a cleaner fracturing system. This includes using a fluid loss additive that is nondamaging. Conventional particulate fluid loss additives are usually made up of inert materials such as silica flour or clay. These types of materials are well known for their ability to plug pore spaces and enhance the formation of a filter cake. Once flow back is started, however, these materials can stay in place possibly causing reduced permeability. Since the materials are inert, they can remain in the pore space for a long period of time. To circumvent these problems, a non-formation damaging particulate fluid loss additive is needed.
This paper describes the development of a new non-formation damaging particulate fluid loss additive that is degradable under downhole conditions. This fluid loss additive is a blend of various starches and substituted starches with a broad particle size distribution ranging from 5 to 200 microns and with a portion of the starches being water soluble.
A synergistic effect occurs between the starches and modified starches that comprise the subject fluid loss additive. This is evident from results seen in standard API fluid loss tests. The blend provides significantly lower spurt losses and Cw values than any of the individual components.
Additional laboratory studies on the non-damaging aspect of this fluid loss additive have shown excellent degradation results with respect to time, temperature, and addition of an enzyme or persulfate.