Experimental research on novel oil displacement and profile control system for heterogeneous reservoir

Abstract

Polymer flooding and surfactant/polymer flooding (SP flooding) were mainly focused on the improvement in oil-water flow ratio and the reduction in oil-water interfacial tension. Preformed particle gel (PPG) flooding was mainly focused on the reservoir heterogeneity improvement. Each of these technologies has its own limitations. Heterogeneous system flooding (HS-PP flooding) was proposed as a novel flooding method aimed to improve oil-water flow ratio and reservoir heterogeneity at the same time. The HS-PP flooding system was composed of PPG and polymer solution. HS-PP flooding, polymer flooding and SP flooding as different chemical EOR methods were studied in laboratory in physical simulation heterogeneous model. Property of cubic expansion of PPG was researched by laser particle analyzer. The result shows that cubic expansion of PPG in simulation water is obvious and can be controlled. The effect of PPG on the diversion rate modification in double parallel sandstone model was obvious. The oil displacement experiments of the three different flooding systems with the same viscosity in physical simulation heterogeneous model were studied. The results show that the HS-PP flooding improves the oil recovery by 20.04%, comparing the result of 12.67% for polymer flooding and 16.66% for SP flooding, respectively. HS-PP flooding as a novel flooding method shows an excellent ability for stabilizing oil production and controlling water cut. The mechanism of the HS-PP flooding was discussed briefly. In addition to the viscoelastic displacement of polymers, the special circulation ability of "accumulating-deforming (collapsing)-accumulating again" of PPG is the main reason why the HS-PP flooding shows an excellent property for stabilizing oil production and controlling water cut.

Effects of residual resistance factor in the mobility control of the polymer flooding

“…Under a high-flow ratio, in accordance with the existing theory and technology, that is, improving the flow control by increasing the viscosity, on one hand, an improper matching of the reservoir permeability to the polymer molecular weight, 22 the polymer viscoelasticity, 23,24 excessive adsorption and retention in the near wellbore area 25 will cause the decrease of the injection capacity, thus restricting the upper limit of mobility control; on the other hand, to effectively reduce the ineffective circulation in high-permeability zones and large pore channels and spawn the dependence on efficient viscosity enhancement systems, the amount of displacement agent injected into the reservoir is increasing, thus increasing the cost and making it difficult to effectively use the remaining oil in nondominant channels and elevating the risk of technical failure. 26,27 Furthermore, even with treatment measures (e.g., parameter optimization, 28,29 good network adjustment, 30 profile control and water shutoff 31,32 ), the flow differences in the reservoir in the vertical and horizontal directions still cannot be eliminated, and the adaptation limits of the polymer flooding in complex reservoirs should be urgently improved. 33 In accordance with the classical theory, the equations of the "resistance factor and residual resistance factor (RRF)" suggest that a high-flow resistance can be established by increasing the solution viscosity, and the RRF can effectively increase.…”