Abstract

Infill drilling programs are one of several projects in place to raise ultimate recovery in Minas Oil Field and are designed to target bypassed oil accumulations between existing producing wells. It is important to learn from the infill wells that have already been drilled so that the success ratio of the drilling project can be raised. We have developed a method to do this called Post Mortem Evaluation. The purpose of this Post Mortem Evaluation project is to compare results of previously drilled infill wells with the criteria used to choose their locations, learn from those successes and failures and to apply that knowledge to defining new criteria for choosing infill well locations to optimize remaining oil recovery.

The basic tools applied were subsurface mapping, petrophysical evaluation (porosity and permeability) and construction of oil pay thickness maps. One primary goal of the evaluation of the previously drilled infill wells was to identify the facies that will not have been drained efficiently due to their heterogeneity. The evaluation was focused on a portion of the Minas field (called IRF) and the work was focused on determining lateral and vertical sand connectivity of the various facies. Stratigraphic cross-sections were built based on high-resolution sequence stratigraphy correlations where wireline log signatures have been calibrated to core data. Subsurface maps, including structure, facies isopach, permeability, water saturation and oil isopach maps, were then generated to understand facies distribution and their petrophysical properties.

The Post Mortem Evaluation indicated that IR-1 was the most successful infill well drilled in the study area, confirmed by the presence of significant remaining oil in this well. The study found that since the main reservoir facies (Amalgamated Channels 1 and 2) had been extensively drained, the prime candidates for remaining oil production were likely Transgressive Channel Fill (TCF) and Prograding Mouth Bar (MB) facies as well as Amalgamated Channel 2 which laterally changes into MB facies. At a higher structural position, oil could remain in Amalgamated Channel-1 facies. By combining stratigraphic analysis with subsurface maps and surrounding well production data, i.e., daily production rate, oil cumulative production and water cut, three new infill well locations were proposed in "IRF area."