--> Optimizing Effort in the Oil Sands: An Experiment to Determine the Relative Benefit of Additional Wells in a Seismic Quantitative Interpretation Case Study

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Optimizing Effort in the Oil Sands: An Experiment to Determine the Relative Benefit of Additional Wells in a Seismic Quantitative Interpretation Case Study

Abstract

Quantitative Interpretation (QI) is a process that results in the prediction of various geological properties (lithology, porosity, fluid, etc.) from seismic data. Although the prediction is ultimately derived from the seismic data, well information is critical to calibrate the analysis and translate the various seismic indicators to the aforementioned geological properties. A question often asked is: How many wells are necessary? For a process that prides itself on the quantitative nature of its analysis, this is one quantity that has so far eluded an answer. A satisfactory answer to this question could inform the efficient exploration and development of a play and provide confident expectations of the outcome. The experiment described in this presentation was intended to answer this question using a densely-drilled 3D seismic survey in the McMurray oil sands area of Alberta. The Cretaceous McMurray formation is a complex sequence of stacked, amalgamated estuarine channels capped by the marine deposits of the Wabiskaw formation. This complexity has necessitated dense drilling to fully characterize the reservoir prior to horizontal well planning for development. Seismic QI can result in a significant cost saving if it is proved accurate with a minimum number of well ties. This project was designed in four phases. A full QI workflow was applied to the seismic data using incrementally more wells in each phase. A total of 79 wells has been drilled on the 19km2 3D to date, however the first QI phase incorporating pre-stack inversion of the 3D seismic data was completed using only 7 wells. The choice of wells for each phase was determined, by the operator, in advance of the project (without any pre-conceived QI-related constraints), based on the order in which they were drilled and the ‘per section’ regulatory requirements. Subsequent phases incorporated an assessment of the prediction of the facies and fluids encountered by the new group of allowed wells, from the results of the previous phase. The new wells were then introduced to the workflow at various stages to assess not only the cumulative effect of additional well data, but also the stage in the workflow where they brought the most benefit. A separate dipole crossplot analysis included all 14 wells with available dipoles. The results will show visual and analytical comparisons of the facies and fluid predictions from each phase and offer an answer to the initial question: How many wells are necessary?