Preformed-Particle-Gel Placement and Plugging Performance in Fractures With Tips

Abstract

Summary Preformed-particle gels (PPGs) have been applied for reducing excessive water production caused by fractures in reservoirs. A portion of the fractures existing in reservoirs is composed of a void part and a fracture tip. The PPG placement behavior and plugging performance could be mainly affected by the fracture tips. A fracture with a tip, called a “partially open fracture” in this paper, was designed to investigate the placement and water-plugging performance of PPG. Cylindrical sandstone cores were used to manufacture partially open fractures. Pressure data of PPG injection, post-gel water breakthrough, and stable injection were analyzed to investigate the PPG propagation and plugging performance with respect to water. Experiments with different PPG placing pressures were conducted to explore the effects of pressure on PPG water-plugging performance and dehydration. In the fractures with tips, the PPG injection pressure increased rapidly, and could reach any designed pressure with continued injection after gel filled the fracture. By setting the PPG placing pressure at 500, 1,000, and 2,000 psi, the blocking efficiency to water showed a growth with the increase of placing pressure. The reswelling experiments show that PPG samples dehydrated when exposed to a high pressure difference between fracture and porous rock. Moreover, the placed PPG dehydrated relatively evenly along the fracture. Some gel particles were found whitening and reducing the capability of reswelling at the placing pressure of 2,000 psi. Scanning-electron-microscope (SEM) images indicated that the distinct 3D network of the PPG was compressed or damaged in the whitish sample. In addition, a discussion about PPG dehydration and fracture-tip extension is provided. In general, this study experimentally characterized PPG placement and plugging performance with respect to water in the fracture with tips. The PPG dehydration and fracture extension in PPG treatment, which have not drawn much attention in the literature, are investigated in this paper.