Control of Unconsolidated Sands in Waste-Disposal Wells1
Sand-control methods were first used in water wells, and modified methods later were applied to oil and gas wells. The most recent application for sand control is in waste-disposal wells. The increasing use of unconsolidated sands as disposal zones has created a need for better sand-control systems.
We suggest that the primary causes of sand-control problems in disposal wells are (1) greater completion intervals, (2) intermittent operation of the well, and (3) chemical characteristics of the injected effluent. Therefore, in order to prevent sand production in disposal wells, consideration must be given to (1) formation characteristics, (2) completion fluid, (3) type of completion, and (4) completion method.
Two universally used methods of sand exclusion, with suggested modifications for disposal wells, are the method of in-place sand consolidation with plastics and fhe use of gravel packs in conjunction with sand screens. Sand consolidation has limited application because of the large completion intervals normally used in disposal wells and because of possible chemical reactions with injected effluent. However, a gravel-pack sand-screen completion generally eliminates the three primary causes of sand production in disposal wells. Factors of prime importance are (1) the drilling and completion fluids, (2) formation grain size and composition, (3) size and amount of gravel, (4) pumping rate, (5) pressure, and (6) gravel concentration.
Field and laboratory data show that the method of gravel-pack sand-screen completions can be used successfully over intervals as great as 585 ft (178 m) in unconsolidated Frio sands.