CASE STUDIES
The Application of Streamline Reservoir Simulation Calculations in the Management of Oilfield Scale
Tharwat Fawzy Ragheb Senior Petro-physicist & Reservior Engineer British Petroleum; BP
Abstract Inorganic scale precipitates in oilfield systems such as down hole in the reservoir, in the production flow tubing, and in surface facilities occur because of thermodynamic changes that affect the flowing brines. These changes may be induced by temperature or pressure changes, or by mixing of incompatible brines which may lead to the precipitation of BaSO4 or SrSO4. The objective of this paper research is to study the application of a streamline simulator that has the appropriate chemistry modeling capabilities to realistic reservoir scenarios. The calculations are performed to demonstrate where and under what conditions scale precipitates take place in the reservoir, and what will be the resulting impact on the chemical composition of the produced brine. Introduction Water flooding is a common method for providing pressure support for oil reservoirs, of which certain production problems may arise after water breakthrough. “The main problem arising from water flooding is that of scale formation caused by incompatible brines mixing, which more gradually occurs if the injected water contains ions that further react with ions in the formation water resulting in the precipitation of inorganic scale – thus making the brines incompatible” (Yuan and Todd, 1991). To understand the previous statement, take for example, if sea water which is rich in sulphate ions is injected into a reservoir with formation water that is rich in barium ions, this will eventually cause the formation of precipitates of barium sulphate in the formation and/or the production wells. “Understanding where and when the scale is more likely to form is very important, since the formation of scale close to or in a production well will reduce its productivity, and in the extreme cases will cause the loss of the well” (Mackay and Sorbie, 2000). 12
March 2011
ECHO
In this paper research, various scenarios will be considered where modeling of in-situ scale precipitation is conducted using the FrontSim reservoir simulation software (FrontSim 2000), this software includes a specialized brine composition and a scale precipitation model to enable such calculations to be made, whilst taking advantage of the reduction in numerical dispersion that may be obtained by performing streamline simulations as opposed to finite different calculations. Streamline Simulation Streamline simulation as stated by (Milliken et al, 2000 and Thierry et al., 1996) is an alternative approach to the conventional finite difference technique. The modeling of fluid flow in hydrocarbon reservoirs as stated by (Mattax and Dalton, 1990) is an Implicit Pressure Explicit Saturation method of simulation in which initially, as with finite difference models, the pressure field is solved implicitly over the whole grid. The next step is where the difference arises, in that the pressure field is then used to trace the path that a single fluid would follow as it flows across the reservoir producing streamlines. The saturations are
“Understanding where and when the scale is more likely to form is very important, since the formation of scale close to or in a production well will reduce its productivity, and in the extreme cases will cause the loss of the well” (Mackay and Sorbie, 2000)
