ABSTRACT:

The Al Jurf oil field, located in the Sabratah basin, offshore Libya, was put on stream in 2003, after having drilled only three exploration and appraisal wells since discovery date thirty years earlier. In order to fine tune the second phase of the development but also to identify potential upsides, it was necessary to tackle at an early stage the substantial subsurface uncertainties of the stacked carbonate reservoirs El Gueria and Chouabine. An appropriate drilling sequence combined with a targeted data acquisition was put in place to that effect. High Tech seismic re-processing (Preserved Amplitude Pre-Stack Depth Migration) was launched as well to address structural and reservoir uncertainties (such as porosity variations). The logging program included imagery logs as it was compulsory to avoid open fractures in well perforations programs but also because the impact of natural fractures on early water or gas breakthrough was poorly known. Production logs were performed in some strategic horizontal wells to understand reservoir heterogeneities (especially permeability variations) and assess the efficiency of the chosen well design. All newly acquired data has been integrated into a geological and reservoir model after drilling only a few wells. This early development data acquisition strategy, combined with the joined efforts of all involved geoscientists, appears to be overall a success: major uncertainties regarding the structural pattern or the reservoir heterogeneity are now better handled and new upsides have been identified (such as the increased potential of the Chouabine reservoir). However the impact of natural fractures on drilling feasibility and on the dynamics of the drainage mechanism is still uncertain: total losses were indeed encountered while drilling some wells. Linking the imagery log information to other data such as seismic attributes and dynamic behaviour, to predict fracture impact, still remains a challenge for the future

This content is only available via PDF.
You can access this article if you purchase or spend a download.