Crushing and embedment of proppant packs under cyclic loading:An insigh to enhanced unconventional oil/gas recovery

Crushing and embedment are two critical downhole proppant degradation mechanisms that lead to a significant drop in production outputs in unconventional oil/gas stimulation projects.These persistent production drops due to the non-linear responses of proppants under reservoir conditions put the future utilization of such advanced stimulation techniques in unconventional energy extraction in doubt.The aim of this study is to address these issues by conducting a comprehensive experimental approach.According to the results,whatever the type of proppant,all proppant packs tend to undergo significant plastic deformation under the first loading cycle.Moreover,the utilization of ceramic proppants(which retain proppant pack porosity up to 75％),larger proppant sizes(which retain proppant pack porosity up to 15.2％)and higher proppant concentrations(which retain proppant pack porosity up to 29.5％)in the fracturing stimulations with higher in-situ stresses are recommended to de-escalate the critical consequences of crushing associated issues.Similarly,the selection of resin-coated proppants over ceramic and sand proppants may benefit in terms of obtaining reduced proppant embedment.In addition,selection of smaller proppant sizes and higher proppant concentrations are suggested for stimulation projects at depth with sedimentary formations and lower in-situ stresses where proppant embedment pre-dominates.Furthermore,correlation between proppant embedment with repetitive loading cycles was studied.Importantly,microstructural analysis of the proppant-embedded siltstone rock samples revealed that the initiation of secondary induced fractures.Finally,the findings of this study can greatly contribute to accurately select optimum proppant properties(proppant type,size and concentration)depending on the oil/gas reservoir char-acteristics to minimize proppant crushing and embedment effects.     

Proppant Crushing Mechanisms Under Reservoir Conditions: Insights into Long-Term Integrity of Unconventional Energy Production

Proppant crushing, a major proppant failure mechanism, occurs in geothermal energy and oil/gas stimulation production stages when the level of net stress exerted on the proppant exceeds the actual crush resistance of the material. Loss of effective reservoir conductivity due to proppant crushing can result in significant loss in productivity, and so it is crucial to understand the realistic proppant mechanical performances under deep reservoir conditions. This review provides a comprehensive overview of proppant crushing at the micro- to macro-levels by analyzing single proppant breakage, as well as re-arrangement and breakage mechanisms of proppant packs under in situ fracture environments. The choice of an appropriate proppant type based on the fracture treatment plays a key role in effective geothermal and oil/gas recovery. In addition, injection of proppants with better characteristics (higher sphericity, lower size, better gradation and lower granular porosity) can significantly influence the reduction of the extent of proppant crushing. Moreover, this study compares the performances and responses of different types of proppants upon proppant interaction with geothermal and oil/gas reservoir environments. Furthermore, this paper discusses various proppant types and their enhanced characteristics, which can be utilized as controlling measures for proppant crushing during unconventional energy extraction.

     

Grain-scale analysis of proppant crushing and embedment using calibrated discrete element models

Acta Geotechnica - Proppant crushing and embedment in hydraulically-induced fractures is a major drawback to the recovery of unconventional oil/gas and geothermal energy production. This study...