Engineering Approach To Designing Fluid Diverters: Jamming and Plugging

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187433, “An Engineered Approach To Design Biodegradable Solid-Particulate Diverters: Jamming and Plugging,” by Mojtaba P. Shahri, Jian Huang, SPE, Clayton S. Smith, SPE, and Francisco E. FragachÁn, SPE, Weatherford, prepared for the 2017 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 9–11 October. The paper has not been peer reviewed. Fluids introduced into a reservoir for stimulation typically take the path of least resistance and, therefore, frequently go into areas with open flow paths. In many cases, those areas are not the targets of stimulation. To maximize contact between the fluid and intact rock, existing fluid paths must be plugged to divert the fluid. A typical fluid-diversion application can be divided into three steps: placement downhole, downhole plugging/diversion, and corresponding stimulation. The aim of this paper is to review and identify critical parameters controlling the downhole plugging/diversion step. Jamming and Plugging Efficiency Successful diversion can be designed and achieved upon full understanding of the jamming and plugging mechanisms that occur at the entrance of existing flow paths. An understanding of the underlying physics of this process allows a system to be modeled that uses the minimal amount of material to create temporary but stable seals that can withstand significant pressure differentials even at flow path openings that are several times larger than the mean particle size. Many complex factors affect diversion efficiency, and they all can be adjusted to minimize flow into existing and highly conductive flow channels. Two major mechanisms control the success of the diversion process: jamming and plugging. In the first stage of fluid diversion within an opening, a stable and jammed structure should be formed by the larger of the particles, which are progressively deposited from a flowing system. In the jamming stage, an initial stable structure is established around an opening (e.g., a perforation during fracturing, a natural fissure, or wormhole during acidizing). The so-called jammed state refers to a configuration in which relatively large particles provide support for one another, remain immobile, and do not pass through the existing opening. As shown in Fig. 1a, the passage of sheep through a gate and the possibility of jamming can be used as an analogy. The size, number, shape, and rate of sheep passing through the gate can determine the possibility of jamming for a specific gate size. Although the passing of relatively large particles (the sheep) is restricted in this stage, fluids and smaller particles (small lambs) can still move through the opening (gate) by using the space between the large particles. Therefore, jamming does not necessarily restrict fluid nor, hence, pressure communication.