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,witha growing number of gas-and-oil fields being developed. Gas-and-oilfields are usually characterized by a complex geological structure,high reservoir heterogeneity, low net-pay thickness, and large gascap, which lead to gas breakthrough, especially in horizontal productionwells. Chemical gas-blocking methods lately have gained more scientificinterest and are becoming more applicable in the fields, the reasonbeing the potential for adjusting the type and properties of chemicalgas-blocking agents (GBA) to increase blocking selectivity. It ishard to numerically simulate the gas-blocking properties of GBA dueto the complexity of their structure and behavior. Flooding experimentsof GBA injection and blocking ability in zones with different permeabilitiesand saturations can provide reliable data to choose the right GBA.However, there are no studies with an experimental comparison of theseveral GBA with a variation of reservoir core permeability and saturation.In this work, blocking ability and selectivity of three hydrolyzedpolyacrylamide-based GBA in the coreflooding experiments were compared:polymer-foam, foam-gel, and gel. East-Messoyakhskoye gas-and-oil fieldfluid and core material were used. This field faced a gas breakthroughin middle-stage development through high-permeability zones into longhorizontal production wells. Coreflooding experiments were carriedout in two stages (injection and breakthrough of GBA) with the simulationof four common reservoir zones: oil-saturated low permeability, gas-saturatedhigh permeability, oil-saturated high permeability, and gas-saturatedlow permeability. Results show that polymer-foam achieved low injectionand medium blocking selectivity. The gel showed higher damaging risksdue to the lowest selectivity in both the injection and breakthroughstages. The best blocking selectivity and blocking efficiency wereachieved by foam-gel due to low initial viscosity and the in situgeneration of a rigid gas-blocking structure.