Acid treatment of bottom hole area is one of the most frequently used methods for well stimulation. It is widely used for the stimulation of horizontal wellbore with hydraulic fracturing and contaminated wellbore. The purpose of the present work is to develop an approach for the acid treatment simulation to increase its efficiency.
The approach provided consists of the set of mathematical models based on the acid treatment simulation techniques on two-dimensional and three-dimensional grids. Acid treatment is described by the model which considers complex fluid composition, any number of kinetically controlled equilibrium reactions and minerals in rock. The use of three-dimensional Voronoi grids allows one to consider geometry features of complex well completions scenarios explicitly. The reservoir type dependent properties are taken into account including the dissolution of contaminations in case of sandstone fractions, heterogeneity of the reservoir, diffusion and mass advection in case of carbonates. The model allows one to simulate flow of multicomponent fluid as well as to consider rheology and temperature of the injected liquid.
Effects of filtration properties anisotropy, the high fracturing degree in carbonate reservoirs, variety of rock mineral composition, secondary and ternary reactions during the acid treatment of sandstone reservoirs were considered. Moreover, non-Newtonian rheology of the fluids in wellbore and reservoir were accounted for and temperature difference in injected liquid between wellhead and bottom-hole was evaluated. The influence of colmatant properties and the degree of bottom-hole and hydraulic fractures contamination on the treatment efficiency were researched. Retrospective analysis of several acid treatments was investigated with detailed simulation of the primary physical phenomena. Simulation results for acid treatment of complex completion well with previous hydraulic fracturing were demonstrated as well as the influence of well layout features and bottom-hole state on the acid treatment outcome.
The technique allows one to perform acid treatment simulation in case of the complex completion scenarios. Three-dimensional grid proposes explicit solution of completion geometry features and provides precise simulation of wellbore fluid flow. The model could perform the bottom-hole and fractures cleaning modeling and simulate the flow in the naturally originated fracture system using the effective media model.

The annual oil production is more than 10 million tons for 20 consecutive years by chemical flooding in Daqing Oilfield. The average oil recovery of chemical flooding is 57.1-64.9 % OOIP. Reservoir properties research has showed that the reservoir after chemical flooding has formed strong water preferential flow paths, although the thickness of which is only 15.9 %, the water absorption ratio is as high as 60 %. In order to further increase oil recovery after chemical flooding, a self-adapting conformance control enhanced oil recovery system which can plug the water preferential flow paths effectively was developed. As the self-adapting conformance control EOR system exhibits special flowing characteristics, it is necessary to develop a suitable mathematical model to accurately simulate the oil displacement process.
This paper has conducted a series of studies for the self-adapting conformance control EOR system, based on which, the mathematical model of the self-adapting conformance control EOR system was developed and applied in the field. Firstly, the 3D visualization porous media microfluidic model was applied to study the microscopic flow characteristics of the self-adapting conformance control EOR system, which showed that the migration process of plugging agent components in the elf-adapting conformance control EOR system is highly selective, driven by the pore and its own microscopic force, it can automatically enter the relatively large pores, so that the oil displacement agent components in the elf-adapting conformance control EOR system can continuously turn to the liquid flow in the pores to produce continuous flow and spread to more small and medium-sized pores. Secondly, the laboratory fractional flow experiment was carried out. The results showed that the self-adapting conformance control EOR system can effectively plug the high permeability layer and improved the fractional rate of medium and low permeability layers. Finally, according to the results of microfluidic 3D visualization experiment and fractional flow experiment, the mathematical model of the self-adapting conformance control EOR system was developed, which can accurately simulate the flow characteristics and oil displacement process of the self-adapting conformance control EOR system in porous media.
The developed mathematical model was applied to simulate a pilot test for the self-adapting conformance control EOR system after polymer flooding, optimizing the injection parameters of the self-adapting conformance control EOR system and predicting the oil production effect. The simulation results showed that the developed mathematical model has strong practicability.