Abstract:

A four foot long pipe (ID 2") packed with silica sand was used to study the effects of formation damage caused by completion and work-over fluids in a high permeability reservoir. Pressures were recorded at five locations (1 foot apart) across the high permeability sand pack as different fluids at a permeability sand pack as different fluids at a rate of 5 ft/day were injected into it. Bentonite and salt concentration of the injected fluids were changed and their effects on the single phase permeability of the sand pack at different permeability of the sand pack at different filtration levels were investigated. Some runs were performed using field water from San Ardo field in California. Finally, effects of formation damage on oil recovery by water-flooding were also studied.

Results show that depending on the composition and the amount of the injected fluids, high permeability sand pack develops irreversible permeability sand pack develops irreversible permeability loss which in turn limits the permeability loss which in turn limits the ultimate oil recovery during water-flooding. Results also show that maintaining proper filtration level can minimize the degree of damage to the high permeability sand pack.

Introduction:

Although many works have been conducted in the past on the mechanisms and consequences of formation damage, high-permeability unconsolidated reservoirs did not receive a fair share of that attention. Recently, Meloy et al. reported on particle movement in capillary network through computer simulation. It is commonly believed, in the field, that these reservoirs can hold up very well against any solids invasion and plugging. It is true that these formations are more forgiving, however, the injection of fluids contaminated with oil and suspended solids can alter both the absolute and relative permeabilities of the porous media and adversely affect oil recovery.

In this study, simulated completion fluids and actual lease water samples were used to determine their formation damage potential in unconsolidated sands with 2.6 to 6 darcies. Invasions of suspended solids and oil emulsions and the extent of damage were recorded at different depths. Relative oil-water permeability ratios and oil recovery of damaged and undamaged sand packs were evaluated. Filtration levels necessary to prevent permeability impairment were also assessed. permeability impairment were also assessed. P. 523

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