Mechanisms of crude oil-sand synergistic plugging of sand control media in heavy oil and unconsolidated sand stone reservoirs

Key words:  heavy oil reservoir  sand control media  synergistic plugging  plugging mechanism  alternating unblocking  steam stimulation

Abstract:

Regarding to the problem of sand control media blockage in sand producing wells of heavy oil, water and heavy oil mixed fluids were used to carry formation sands, conducting sand blocking displacement experiments with two modes of one-way displacement flow and thermal production alternating hubble-spit flow. The plugging mechanisms and flow behavior of heavy oil-formation sands were revealed with multiple sand controlling media, including three screens and gravel layers of slits, wire winding, composite screen, and multiple sand retaining media of composite screens under different conditions. A prediction model to evaluate the plugging degree of sand control media by heavy oil-formation sands was proposed. The results show that high viscosity heavy oils have an obvious blocking effect on the porous media of the sand control layer, and the permeability damage can be up to 70% depending on the viscosity and flow velocity of the heavy oil. In heavy oil sand control wells, there exist complex and synergistic plugging mechanisms of heavy oil and formation sands to the sand control media. Heavy oil can occupy the medium space in the form of binding oil, aggravate the blockage of internal separation bridge, which can cause a permeability damage of more than 90%, meanwhile the sand retaining effect can be improved. In the thermal recovery process of steam injection, the alternating huff and puff production mode can have an obvious plugging relief effect on the plugging of heavy oil and formation sands. However, with the increase of injection-production cycles, the capability of plugging removal and permeability recovery can be gradually decreased. The synergistic plugging of heavy oil-formation sands under different production modes is obviously related to the viscosity of heavy oil, oil production rate, flow rate and other factors, which needs to be considered to evaluate the dynamic productivity of heavy oil sand control wells. For the sand control medium precision design of heavy oil reservoirs, it is recommended to relax the sand control precision of conventional oil reservoirs by 1-2 levels.