Recent Enhancements for 3D Seismic Interpretation: Visualization, Image Processing and Attribute Analysis

Abstract

Abstract 3D seismic is becoming the standard tool for both exploration and production stages of development. To meet the increasing demands, new ways are being developed to quickly extract and analyze all the information contained in the 3D seismic data. Methods now exist to view large 3D seismicvolumes and quickly generate interpretations on key horizons, In addition, potential prospect size hydrocarbon volumes within the larger seismic dataset can be quickly identified for further analysis. Tools are also available to enhance surface resolution using image processing on prospective horizons. After volume and surface visualization is complete, mathematical waveform attributes are extracted from the key seismic horizons for statistical correlation to physical rock properties important to prospect success. These physical properties may include a wide range of reservoir parameters such as porosity or thickness. These interpretation techniques were used to evaluate a 3D survey at Fortescue Field (Gippsland Basin, Australia) before starting a 13 well infill drilling program in 1994. Drilling results indicate these interpretation methods were successful in three ways. First, new drilling locations were found that were not previously identified using more conventional methods. Second, identified drilling locations were more precisely positioned to maximize economic benefit. Third, the risk associated with each drill location was reduced allowing otherwise unattractive wells to be drilled. Adler 8 drill wells, the average error in reservoir thickness prediction was 0.43 meters. Introduction Oil was discovered in the top of the LaTrobe Group (Eocene) at Fortescue Field (Fig. 1) in 1978 (Ref. 1). Following appraisal drilling and platform installation, production started in 1983. To mitigate recent production decline and develop remaining reserves, a 13 well infill drilling program was proposed in 1993, Structurally, the field is a west-southwest dipping monocline (Fig. 2) with oil trapped stratigraphically beneath an erosional unconformity in 13 separate clastic reservoirs. An east-west seismic line (Fig. 3) over the field shows this relationship, The reservoirs dip approximately 2 degrees more steeply than the overlying erosional truncation surface, causing older sections to progressively subcrop in an easterly direction (Fig. 4). Ail the proposed infill wells relied completely or partially on oil being trapped structurally updip from existing completions. To effectively capture these reserves, wells were targeted to intersect reservoirs along the low-angle sand truncation face (Fig. 5). The ability to identify and map the top and base reservoir edges along the subcrop surface was critical for well success, Ideal well penetration points should be in the most updip location and still encounter the estimated 5-10 meters of sand necessary to yield economic daily oil volumes The goal of the study was to quickly and accurately identify 9 reservoir subcrop edges, determine the remaining reserves updip from existing completions and identify the geological risk associated with each drill well.