Sand production and solid control optimization in deep carbonate reservoirs

Key words:  carbonate rock  complex production of argillaceous sandstone blocks  solid control  precision optimization

Abstract:

Borehole wall collapse and sand production are of great concerns during oil and gas production process from carbonate reservoirs, in which rock blocks, cuttings and sands can be accumulated in wellbore, causing blockage and reducing the productivity of the oil well. In this study, a multi-functional sand displacement performance evaluation device was used to conduct experiments of borehole wall collapse and sand production in carbonate reservoirs. Metal mesh slices with precision of 250,350, 450 and 550 μm and sand samples from three typical unstable wells were used in the experiments. Sand retention and liquidity of sand retaining medium were quantitatively evaluated using the dynamic data of pressure and flow rate, and the feasibility of solid control was analyzed and its precision was optimized. The experimental results show that the metal filter with a precision of 250-550 μm can be used to effectively block sands with a medium size of 289.5 μm and cuttings/blocks or pure sands with a medium size of 40.3 μm. The sand passing rate of the sand retaining medium was less than 12% and the plugging equilibrium permeability was more than 1.3 μm², indicating that the solid control for carbonate unstable wells is feasible. The results of screen precision optimization show that for the composite production of sands with a medium size of 289.5 μm and cuttings/blocks in carbonate reservoirs, it is recommended that the screen precision should be of 0.5-0.6 mm, or the screen precision should be appropriately expanded on the premise of ensuring sand retention performance. For the production of pure sands with a medium size of 40.3 μm,the screen precision can be improved to 0.3-0.4 mm. Production with a moderate sand carrying or sand-out is recommended for high yield wells in carbonate reservoirs.