Improved understanding of proppant embedment behavior under reservoir conditions: a review study

Proppant embedment, which occurs at depths in rock formations, is a key proppant downhole mechanism which can result in rapid decline in hydrocarbon production. The current review study reveals that both rock formation characteristics and proppant characteristics significantly determine the embedment mechanism. Importantly, the review shows that embedment can occur in any formation, whatever the type of rock, leading to conductivity loss in siltstone of 78.42%, in mudstone of 81.89%, in conglomerate of 91.55%, and in shale of 78.05%. The present study investigated the importance of the creep phenomenon (a function of confinement and temperature), the percentage of clay content, and surface roughness on proppant embedment. Other dynamics, such as time, temperature and fracture fluid, can also impact the rate of proppant embedment as they help to alter the softness (young's modulus) of the fracture surface. This study reveals that curable resin-coated sand (embedment of 44 μm) is very tolerant of the embedment process compared with lightweight ceramics (113 μm) and uncoated fracture sand (106 μm). Similarly, higher proppant concentration, greater proppant size, uniform proppant distribution and a greater number of proppant layers can minimize the embedment process to a great extent, ensuring the effective extraction of oil/gas from hydraulically fractured wells. This paper also reviews some existing numerical and analytical models on proppant embedment which enable forecasting of the fracture conductivity loss undergone in downhole fracture treatments. Finally, the paper summarizes some of the case studies emphasized on proppant embedment effect and various research recommendations are suggested to minimize the proppant embedment.