In an oil field development, the choice of the appropriate artificial lift method is extremely important to obtain the best financial return for the project. The most efficient artificial lift method for heavy oil is the ESP, in the perspective of lift capacity and flow assurance, but, due to its low MTTF (Mean Time to Failure), in some cases, the associated cost for the offshore workovers is prohibitive. An alternative to reduce the cost of the workover is positioning the ESP in the seabed, in a pumping skid (Subsea ESP / skid-ESP). Positioning the ESP in the seabed, however, reduces the initial well flow rate. Most commonly, the Artificial Lift Method is chosen based on the previews experience of the operator, not giving appropriate effort to a technical and commercial evaluation. This paper proposes a methodology to provide quantitative data to assist the decision of the best positioning of the pumping system, inside the well or on the seabed, in order to obtain the best financial return.
The methodology is based on three stages: technical evaluation, which is an eliminatory step, based on the GVF (Gas Volume Fraction) limit that the pump can handle without flowing problems; then, an economical and risk analysis are performed for both projects (ESP and skid-ESP). Three case studies were performed to evaluate the proposed methodology, and to confirm that it is a good tool to assist the decision of the best positioning of the pumping system.
The results show that the three stages proposed are important. One of the three cases show a scenario where the skid-ESP is declassified in the first step of the methodology because of the high GVF calculated for the project, above the limit for this specific well. In the other two cases all the three stages of the methodology were applied. The economical deterministic analysis was not enough to define the best positioning of the pumping system, in order to obtain the highest financial return, and the probabilistic risk analysis was essential to obtain quantitative data to support an efficient decision. In both cases the suggested positioning of the pumping system was the seabed (skid-ESP or subsea ESP).
In the literature, some works propose methodologies to choose the appropriate artificial lift method. Some of them offer an economical evaluation tool; but a methodology that includes the subsea ESP as an option for heavy oil deep water projects was not found in the literature. This paper proposes a methodology that can be easily applied with the software's commonly used in the industry, therefore adding information to the existing body of literature that can benefit practicing engineers.