Abstract
Can management and partners be convinced to acquire a new 3D high-resolution survey (3DHR) less than three years after acquiring a high quality, conventional 3D? This is what was proposed in 1999 in the deepwater (>1300 m) Girassol Field, offshore Angola block 17—one of TotalFinaElf's largest deepwater projects. The business objective: To make a tangible impact on appraisal and development programs, and ultimately use the new seismic as a baseline survey for 4D monitoring. This article describes the key steps to prepare, acquire, process, and interpret the 3DHR. Preparation included a feasibility study to determine if a new survey was the best economic and scientific route and then to define the optimal acquisition design. CGG was awarded the contract for the 3DHR seismic acquisition and processing. Acquisition required enhanced onboard quality control by CGG and TotalFinaElf, optimal control of acquisition parameters because the source was at a shallow depth, and efficient logistics. Processing included a first pass, 300-km2 fast track volume of four million traces delivered five weeks after the last shot, and final volumes (near and far) with standard poststack time migration after DMO. Special attention was given to preserving the large frequency bandwidth at all stages of processing. Interpretation generated a reservoir model that was more heterogeneous than initially foreseen because the 3DHR nearly doubled spatial and vertical resolution, enabling the interpreters to construct a refined geomodel from inverted impedances and other seismic attributes. Impact: The design of appraisal and development wells was optimized in the field, reducing the total number of wells by 25% compared to field planning with the original 3D seismic. The key ingredients of this success are: (1) solid technical arguments and performance focused on operational and business issues; (2) close interaction between the operator and the geophysical contractor with a detailed QC …
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