Abstract
Abstract The paper evaluates application of CO2 injection for the control of water encroachment from the aquifer into gascondensate reservoir under active natural water drive. The results of numerical simulations indicated that injection of CO2 at the initial gas-water contact (GWC) level reduces the influx of water into gas-bearing zone and stabilizes the operation of production wells for a longer period. The optimum number of injection wells that leads to the maximum estimated ultimate recovery (EUR) factor was derived based on statistical analysis of the results. The maximum number of injection wells at the moment of CO2 break-through into production wells for homogeneous reservoir is equal to 6.41 (6) and for heterogeneous – 7.74 (8) wells. Study results indicated that with the increase of reservoir heterogeneity, denser injection well pattern is needed for the efficient blockage of aquifer water influx in comparison to homogeneous one with the same conditions. Gas EUR factor for the maximum number of injection wells in homogenous model is equal 64.05% and in heterogeneous – 55.56%. Base depletion case the EURs are 51.72% and 49.44%, respectively. The study results showed the technological efficiency of CO2 injection into the producing reservoir at initial GWC for the reduction of water influx and improvement of ultimate hydrocarbon recovery.
Highlights
Rational development of gas-condensate fields under the active water drive is based on systematic control of aquifer water influx into the gas zone and water breakthrough to production wells [1, 2]
During CO2 injection into homogeneous reservoir model the duration of production well operation depends on number of injection wells and respectively equal for 4 wells – 44 months, for 6 wells – months, for 8 wells – months, for 12 wells – 40 months and for 16 wells – 34 months
Analysis of reservoir pressure behavior at the time of CO2 break-through into production wells indicated that increase of injection wells number from 4 to 8 in case of heterogeneous model leads to higher values of reservoir pressure in comparison to homogeneous one
Summary
Rational development of gas-condensate fields under the active water drive is based on systematic control of aquifer water influx into the gas zone and water breakthrough to production wells [1, 2]. During field development planning stage geological information is limited, and a special attention must be paid to the selection of well locations for maximum drainage of the reservoirs [1]. Non-uniform production well spacing with higher well-count in the crest of the gas-bearing zone is very common. These leads to selective water encroachment into the gas zone through high-permeable rocks and most depleted layers [4]. Selective water invasion causes decrease of gas relative permeability and well productivity due to liquid loading, when mixture velocity in the tubing falls below the critical value of 4-5 m/s
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