Analysis of Operative Variables for Establishing a Procedure to Obtain Representative Fluid Samples in Gas/Condensate Fields

Abstract

During the exploratory phase, reservoir fluid analysis is an important tool for obtaining the hydrocarbon volume In-Situ, for understanding the behavior of fluids based on the field pressure changes, for defining a fluids production strategy, and as an input for production facilities design, among others. Due to the importance of this information, sampling procedures must guarantee that collected fluids are representative of reservoir ones to allow for reliable results which will be obtained during the PVT laboratory studies.In the ABC Fieldcase, located in Cusco Peru, a Gas-Condensate reservoir with a dew point close to the initial reservoir pressure, it was necessary to develop a detailed operative design in order to guarantee that fluid samples would be representative. This study allowed us to define some steps which must be present in the operative procedure in order to achieve an optimum sampling process.Additionally, it was possible to see the effects in the representativeness of the samples due to pressure depletion, condensate banking, and its compositional analysis. The behavior of the Gas-Condensate ratio, the turbulent flow effects in the formation face, permeabilities, the optimum time for sampling, and flow rates.Finally, it was possible to evaluate the sampling procedure effects and its influence in the representativeness of fluid. An equation of state tuning was carried out for two fluids which were sampled in the same well. In this case, the effects of the different sampling procedures and their repercussions in liquid recovery are analyzed.With the information contained in this study, we can identify the importance of selecting an exclusive sampling period outside of the normal transient pressure testing period and the effects of the main system variables. Keeping in mind the importance of this information and the costs associated with the project, failure is not an option.