Evaluation of Natural Fractures and Their Impact on Gas Production Using Image Logs (Sirte Basin, NE Libya)

Abstract

The Cambrian-Ordovician Gargaf Formation, in the central part of Sirte Basin, is considered as one of the main reservoirs for gas production as in Alestiqlal field. The petrophysical properties of the reservoir revealed very low matrix porosity and permeability and can be classified as a tight reservoir. Auspiciously, the presence of natural fractures is considered as a vital element for the reservoir production. Therefore, evaluating such features becomes mandatory for Sirte Oil Company (SOC) for optimum reservoir characterization and management. Taking that into consideration, image logs were acquired by SOC in most of the drilled wells in the field. Integrated borehole case study was conducted for 10 wells to evaluate both natural and drilling induced fractures as well as the sub-seismic faults from image logs. The results represented by fractures orientation and intensity are used to examine the relationship and impact of natural and drilling induced fractures on gas production. The identified present day maximum horizontal stress indicated that a certain trend of the natural fractures relative to the maximum horizontal stress is controlling the reservoir productivity performance of Gargaf reservoir in Alestiqlal Field.