Numerical modelling of salty reservoir waterflooding with fresh water
- Kirill Bogachev (Rock Flow Dynamics) | S. V. Milyutin (Rock Flow Dynamics) | V. I. Dzuba (TNK-BP)
- Document ID
- Society of Petroleum Engineers
- SPE Russian Oil and Gas Exploration and Production Technical Conference and Exhibition, 16-18 October, Moscow, Russia
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.5 Reservoir Simulation, 5.1 Reservoir Characterisation, 4.3.4 Scale, 1.6 Drilling Operations, 5.3.1 Flow in Porous Media, 5.4.1 Waterflooding
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In this article, a reservoir waterflood numerical modelling problem is considered for the case when injected water salinity is different from formation water salinity, and taking into account mass transfer due to reservoir salt dilution. Based on a multiphase isothermal black oil model, a new mathematical model is proposed, taking into account the basic physical parameters of the underlying process, such as maximum salt concentration (saturated solution concentration), viscosity and water density dependence on salt concentration, porosity and permeability changes during dilution. It is assumed that dilution speed is proportional to current and saturated solution concentration difference. This model was programmed in a commercial parallel hydrodynamic reservoir simulator  and was tested on real field models, showing high numerical effectiveness.
Oil reservoir waterflooding is a basic oil production technology. It consists of organizing waterflood systems that could support reservoir pressure by injecting water through injector wells drilled in the reservoir according to some specified order. Besides other numerous factors that influence waterflooding and determine its effectiveness, the most important one is injected water composition. Currently, each field has recipes and requirements for injected water (including it's salinity characteristics) and the conditions of injected and reservoir water compatibility are formulated. Produced water probes are taken and analyzed regularly, this is an objective and reliable means of field development control that can help with flow identification.
Since new fields with salinated reservoirs (porous media with high salinity 10-50%) are discovered, and there's not much waterflooding experience for such fields, it's of immediate interest to simulate development of such fields using mathematical models adequately representing physical processes. Known descriptions of such processes, claimed to be correct, require complementing usual porous media flow equations with dozens of new additional algebraic and differential equations. It is clear, that from a computational point of view, such "exact?? descriptions are unrealistic for simulation models of reservoirs with hundreds and thousands of wells. The other and more important point is the uncertainty of defining necessary reservoir properties in the interwell area, such as hydrolysis reaction parameters, salt composition etc. These parameters substantially influence the flow processes. Due to this uncertainty, together with the need to make existing models substantially more complex, it became necessary and relevant to look for more robust and universal approaches. This article proposes a numerical highly effective mathematical model, using such additional parameters to describe physical phenomena on the reservoir scale, which are minimally sufficient and can be measured.
It should be noted that currently in many commercial hydrodynamic simulators there is an option to allow tracing salt water in the black oil model framework, taking into account the water viscosity and density dependence on salt concentration, but ignoring reservoir salt dilution. Salt dilution can be modelled only in a compositional model framework, thus decreasing simulation numerical effectiveness (numerical stability decreases, calculation time goes up) and requiring a large number of additional parameters. The model and its implementation proposed in this article are complementing the existing salt water tracing option, and this defines it's practical attractiveness.
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