Different Methods of Modeling Tilted Free Water Levels and the Impact on Field Production

Abstract

Abstract This paper presents and compares the results of the creation of a titled Free Water Level (FWL) from two different modeling methods and the impact on field production. Worldwide there are examples of oil and gas fields with tilted FWL's. These can be generated by different mechanisms. This paper focusses on the modelling of a tilted FWL associated to a hydrodynamic system. There are several methods of modeling a tilted FWL, most of them emphasize on how to create a tilted FWL but lack the correctness of pressure distribution. Two modelling methods were investigated and their results were compared. One is a static method in which a tilted FWL surface is assigned and the respective water saturation (Sw) values are calculated in the model. The second approach is a hydrodynamic method based on the hydrodynamic principle that a tilted FWL is generated by lateral pressure variation related to a water flow below the hydrocarbon bearing interval. Both methods can generate a correct tilted FWL surface and the associated water saturation distribution, but the pressure distribution shows a significant difference depending on which method was applied. The hydrodynamic method delivers a correct pressure distribution in both the hydrocarbon and the water zone as it captures the physical principals of the tilted FWL and aquifer and therefore the corresponding pressure data. In the field-model a realistic stronger pressure support can be observed, leading to realistic recovery figures. The static method provides a correct pressure distribution in the hydrocarbon zone but not in the water zone, and delivers a nonrealistic weaker pressure support, leading to lower production figures. The fundamental difference in pressure distribution has a signiciant impact on a field production and therefore project economics. In conclusion, proper tilted FWL modeling should provide not only a correct FWL surface but also pressure distribution. In cases where a tilted FWL is associated to water flow below the hydrocarbon zone, the hydrodynamic method based on the hydrodynamic principle is recommended.