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Evaluation of the performance of physical model based miscible displacement modelling techniques

Tiptiris Ioannis

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Summary

The oil and gas industry has developed over the years powerful and reliable tools (e.g. reservoir simulators) to simulate the oil recovery process. Complex production scenaria, such as EOR projects, specifically CO2 injection ones, can be simulated in detail. Such tools however are very complex and require very detailed data as input which in many cases is not available. What is more significant is that time and resources (both human and economic) need to be spent to evaluate production scenaria that might prove to be not profitable at all. The need for the development of quick and low cost tools to make a first screening in order to decide whether the project is a potential, profitable candidate, or if no further research is required due to very low expected recovery, is due. The objective of this thesis is to combine two existing simulation methodologies, one relying on basic analytical relationships and the other on fundamental 2D-simulation techniques, into such an integrated screening tool which will allow the engineer to make a first sort and decide which projects require further detailed investigation.The first part of the integrated screening tool is based on Zero-Dimensional Mapping, a volumetric technique comprising of simple Material Balance calculations. The second part is based on Streamline-Streamtubes Numerical Simulation and is implemented by a commercial software developed by Texaco Exploration and Production Technology Department, named “CO2 Prophet”. Two examples referring to secondary and tertiary production respectively, both utilizing CO2 injection, were taken by the classic textbook of Green and Willhite for “Enhanced Oil Recovery” and used to verify the credibility of the developed screening tool. The results have shown that the developed tool predicts accurately both the form of the recovery curve and its values as the observed differences between the two methodologies are of the order of 4% OOIP which is a decent match.Although the integrated screening tool predicts successfully the two basic scenaria, real world projects involve uncertainties in many variables (e.g. reservoir heterogeneity) that the Zero-Dimensional Mapping model cannot “sense” due to its designed simplicity. However, “CO2 Prophet” uses such variables as inputs, which allows the user to test the sensitivity of the whole project to any possible uncertainty. In order to investigate the software capabilities on that arena further, three case studies regarding the Dykstra-Parsons coefficient (V), the number of reservoir layers and the minimum miscibility pressure (MMP) value were conducted. The results have shown that the V coefficient has a major impact on recovery giving huge differences in recovery for the different cases studied. On the contrary, the number of layers affects the recovery a lot less. As for the MMP estimate, the results have shown that the flow pattern (miscible, immiscible) which is defined by the MMP plays a significant role in recovery and while some uncertainty in the MMP estimation is tolerable, the flow pattern must always be ensured.

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