In-depth gel treatment has become an attractive technology for those water-flooding oilfields with thick heterogeneous net pay zones. Numerical simulation was run to analysis the effect of some geology characteristics and gel properties on gel treatment results. A typical nine-spot unit model was built in this paper, based on the reservoir characteristics and production history of X oilfield, which is characterized by high permeability, thick oil layer with severe heterogeneity and high oil viscosity.
Results show that gel treatment results is a function of injection volume, formation heterogeneity, ratio of vertical and horizontal permeability, gel strength, gel degradation rate, injection occasion, and injection methods. Gel treatment efficiency increases with formation heterogeneity and decreases with the ratio of vertical and horizontal permeability due to increasing damage of gel on low permeability zones. Gel treatment shows better efficiency in low water-cut stage thanthat in high water cut stage, but potential damage of gel on low permeability zones will limit gel application in early stage of oilfield development if gel is injected without zone isolation. The damage of gel on low permeability part of thick layer will be reduced if high permeability part of thick layer is isolated and gel is only injected from the high permeability part, even though no barrier in the thick layer. Gel treatment efficiency also depends on gel volume, gel degradation rate and gel strength. Combing technology of polymer and gel treatment shows better results for our model, and polymer flooding following gel results in better efficiency than gel following polymer flooding.
X is an offshore sandstone oilfield in China. The oilfield is characterized by high oil viscosity (about 50~100 mPa at the conditions of formation temperature and pressure) and high permeability contrast both in horizontal and vertical direction (from several md to more than 10,000 md). The total net thickness of oil layers is above 40 m for each well. Thick oil layers are widely distributed in the oilfield (from several meters to more than 15 meters). The porosity is high to 23~37%. The oilfield has been developed since 1993. The average water cut is about 37% until the end of 2001. Water cut of some producers are more than 80%. To control water cut and increase the oil production rate and oil recovery of the oilfield, some IOR (Improve Oil Recovery) methods are designed.
Until now, many technologies have been successfully applied to control conformance in water flooding, such as polymer flooding, foam flooding, and surfactant flooding and so on. Recently, injecting large volumes of gel to correct in-depth permeability for those reservoirs with high heterogeneity has become an attractive technology to control water cut and improve oil recovery [1–6].
This paper assumes gel treatment as one candidate for improving oil recovery and controlling water cut of the oil field. As we know, many factors influence gel treatment efficiency, including reservoir geology characteristics, well conditions, gel properties and operation technique during gel treatment [7–10].