Coreflood Testing of Gas-Blocking Agents: Selectivity in High-Heterogeneity Reservoirs and Efficiency in Low-Temperature Conditions

Gas breakthrough is becoming an increasingly common problem, with a growing number of gas-and-oil fields being developed. Gas-and-oil fields are usually characterized by a complex geological structure, high reservoir heterogeneity, low net-pay thickness, and large gas cap, which lead to gas breakthrough, especially in horizontal production wells. Chemical gas-blocking methods lately have gained more scientific interest and are becoming more applicable in the fields, the reason being the potential for adjusting the type and properties of chemical gas-blocking agents (GBA) to increase blocking selectivity. It is hard to numerically simulate the gas-blocking properties of GBA due to the complexity of their structure and behavior. Flooding experiments of GBA injection and blocking ability in zones with different permeabilities and saturations can provide reliable data to choose the right GBA. However, there are no studies with an experimental comparison of the several GBA with a variation of reservoir core permeability and saturation. In this work, blocking ability and selectivity of three hydrolyzed polyacrylamide-based GBA in the coreflooding experiments were compared: polymer-foam, foam-gel, and gel. East-Messoyakhskoye gas-and-oil field fluid and core material were used. This field faced a gas breakthrough in middle-stage development through high-permeability zones into long horizontal production wells. Coreflooding experiments were carried out in two stages (injection and breakthrough of GBA) with the simulation of four common reservoir zones: oil-saturated low permeability, gas-saturated high permeability, oil-saturated high permeability, and gas-saturated low permeability. Results show that polymer-foam achieved low injection and medium blocking selectivity. The gel showed higher damaging risks due to the lowest selectivity in both the injection and breakthrough stages. The best blocking selectivity and blocking efficiency were achieved by foam-gel due to low initial viscosity and the in situ generation of a rigid gas-blocking structure.