Enhance exploration in high-uncertainty formations

The Arabian Gulf Oil Company (AGOCO) had exploration wells accessing the Memouniat and Acacus sandstone formations in the Libyan portion of the Ghadames basin. The geometry of these sandstone units is not fully demonstrated, and there are numerous uncertainties involving the reservoirs' lateral uniformity and continuity—even within a few kilometers' distance. Without accurate data for characterization and formation evaluation of the facies, determining their distribution and correlation was challenging.

In these formations, identifying facies based on traditional openhole logs is unreliable and cannot be used to construct a definitive facies model. Limited core data, from which sedimentological and directional information can be obtained, was recognized as a source of potential difficulty in creating a robust geological model. Previous-generation, conventional openhole logging techniques showed good agreement in log response between adjacent wells, but AGOCO wanted to know whether better-informed decisions based on higher accuracy petrotechnical data were possible.

Improve geological modeling with accurate data

The basic openhole logs indicated that the sandstone units of the Acacus and Memouniat reservoirs had no marked facies variations and therefore could be assumed to share similar depositional conditions. This conclusion could have led to suboptimal field development decisions. Advanced petrotechnical interpretation using recently acquired data proved that the sandstones had very different facies characteristics than previously thought.

Schlumberger petrotechnical experts collaborated with AGOCO to design a measurement-acquisition plan that included deploying the FMI fullbore formation microimager as a standard log in its exploration wells in the basin. FMI microimager details can be discerned down to 50 um and can help describe intervals where no coring and sampling data was obtained. After the petrotechnical team processed the microimages, they performed a detailed dip interpretation and integrated elemental analysis and elemental capture spectroscopy results. Finally, the team created a high-resolution microfacies log to construct and interpret a decisive 3D facies model of the wells in the Ghadames basin.

Microfacies interpretation is useful for describing the subsurface stratigraphy of clastic facies in basins with high vertical and lateral sedimentological complexity. Additionally, microfacies analysis describes sandstone reservoir properties that exhibit extreme petrophysical behavior and aid in determining different well-correlation methods for the Ghadames basin wells. The petrotechnical interpretation helped determine the specific positions in stratigraphic cycles in which sandstone facies with good-quality reservoir properties were more likely to occur.

Better understand subsurface variations with expert analysis

The AGOCO and Schlumberger team demonstrated the importance of applying detailed interpretation techniques to multiwell facies analyses for better-informed subsurface characterization and exploration decisions. This petrotechnical interpretation helped identify high-quality intervals for fracturing, testing, and perforation in the stratigraphically and sedimentologically complex basin. Optimizing the selection of these intervals saves money and time as well as increases production from the zones or facies. On the basis of the results of the in-depth petrotechnical evaluation, AGOCO decided to run the FMI microimager as part of its standard logging tools in exploration wells.