Borehole Image and Production Logging Drives Well Interventions in Horizontal Gas-oil Gravity Drainage Wells in a Giant Middle Eastern Carbonate Field
Edward Follows, Andrew Beck, Andrew Farmer, Saud Al Salmi, Gerbert de Bruijn, Livio De Pieri, Rudy Welling, 2010. "Borehole Image and Production Logging Drives Well Interventions in Horizontal Gas-oil Gravity Drainage Wells in a Giant Middle Eastern Carbonate Field", Dipmeter and Borehole Image Log Technology, M. Pöppelreiter, C. García-Carballido, M. Kraaijveld
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Some recent insights are presented into a fractured carbonate oil-rim development in Oman that is produced through both gas-oil gravity drainage (GOGD) and waterflood. Resistivity borehole image (BHI) data are used to characterize the matrix and fractures of the open-hole reservoir sections of the horizontal GOGD producers. Cores in vertical wells were used to calibrate image logs for matrix and fractures confirming, for instance, nodular fabrics seen in BHI. The BHI data are combined with mainly recently acquired production logging tool (PLT) dynamic data in GOGD producer wells to understand the dynamic behavior of matrix and fractures. Six case histories are used to show how this understanding has been used to relocate wells to reduce gas cuts, and through well interventions, isolate water influxes, and attempt to isolate gas influxes.
The BHIs show a conductive fracture population that was divided into three main types based on increasing apparent aperture. The distribution of fractures partly reflects a mechanical stratigraphy. The wackestone to packstone coarsening cycles carry increased numbers of fractures with reduced fracture spacing and wider apertures in the packstone reservoir sublayers. Attempting gas shutoff in these layer-bound fractured intervals has not yet been successful.
A general absence of fractures in the commonly underlying nodular wackestone layers of the GOGD system is observed. Well trajectories targeted specifically into these nodular wackestones, particularly in the lower Natih C2, have avoided fractures associated with overlying packstones with successfully reduced gas cuts allowing continuous instead of cyclical GOGD production.
In addition to the layer-bound fractures, through-going fracture networks impact individual wells. Both aquifer and water injection influxes through such fractures have been successfully shut off, suggesting that the fracture networks are relatively isolated. These shutoffs have allowed previously noncontributing matrix to produce oil.
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Borehole imaging is among the fastest and most accurate methods for collecting high resolution subsurface data. Recent breakthroughs in acquisition, tool design, and modeling software provide real-time subsurface images of incredible detail, from the drill bit straight to a workstation. Associated interpretation workflows offer the high level of detail that is needed to make operational decision and to increase the predictability of subsurface models. Many exploration and production companies have acquired a wealth of dipmeter and image log data. The data are readily available and provide, for example the orientation of fractures and fluvial channels in space. Further applications of borehole imaging technology include matrix and fracture characterization, pore-type partitioning, geosteering, and in-situ stress determination. Exciting new applications are found in enhanced oil recovery, carbon dioxide sequestration, and geothermal projects. In addition, borehole image data are paramount to unlocking unconventional plays such as shale gas and coal-bed methane. AAPG Memoir 92 portrays key applications of dipmeter and image log data across the exploration and production life cycle. (Continued)