Gravel packs are commonly used to minimize sand production in unconsolidated sandstone reservoirs. The migration of particulates and fines into the gravel packs often has a severely reducing effect on the permeability of the packs and the subsequent productivity of the well. Detailed laboratory studies were undertaken using 12/20 and 20/40 mesh silica gravel to ascertain the optimum gravel size to minimize formation damage to gravel packs in the Battrum field.
The Battrum field is a shallow unconsolidated sandstone reservoir located in Saskatchewan, Canada, producing a low API gravity crude oil over an area of approximately 3900 hectares with 180 active injection and production wells. Currently a large portion of the field is under enhanced recovery using a commercial scale in-situ combustion technique. The results of detailed laboratory studies, including detailed size and sieve analysis of the formation, classification of the different lithologies and detailed laboratory tests to investigate at reservoir conditions the flow of gravel and fines into different sizes of gravel packs are documented. Tests include detailed petrography and computerized petrographic image analysis on actual sections of gravel and formation sand interfaces and illustrate the mechanism of fines entrainment in the gravel packs and provide associated permeability reduction data. Details of field gravel pack treatments are also provided in the paper. Test results indicated an increased propensity for gravel pack plugging in the coarser (12/20) mesh gravel in comparison to the 20/40 mesh gravel. Simultaneous multiphase flow of both oil and water was also found to have an increasing effect on rapidity and severity of apparent plugging. The results presented provide insight into optimum gravel to sand sizing ratios for this field and have potential application to other similar reservoirs.