Tight oil reservoirs are of paramount importance for an operator holding several fields with important oil potential in Illizi basin, southeastern Algeria. Formation tightness, the presence of nonconnected sand lenses, and the lack of a geological model made it very difficult to maintain the oil production in the studied Devonian reservoir. Consequently, the service company and operator adopted an integrated approach to devise solutions that could restore production in a mature tight oil field that had been closed in 2011.
Construction of a geological model for the studied reservoir was challenging because of the high uncertainty in water saturation interpretation caused by the formation water properties (fresh water). A multifunction pulsed neutron service was proposed to provide standalone cased-hole formation evaluation and reservoir saturation monitoring. A unique modeling approaches was applied to characterize the studied tight reservoir and evaluate the reserves based on advanced uncertainty analysis. A hydraulic fracturing design workflow in a reservoir centric stimulation to production software was developed using an integrated approach (geological and geomechanical models) to place the fracture in the optimum reservoir quality and connect the sand lens bodies.
Two existing wells were selected to run with the pulsed neutron service, resulting in acquisition of comprehensive reservoir rock and fluid content data. The interpreted logs served to reduce the uncertainty in water saturation modeling and to enable perfect history matching of the producing wells. The constructed geological model was the basis for improving the stimulation designs and maximizing production for future wells. With significant oil initially in place (STOIIP) estimated from the model, the field showed more promise than the previous recorded recovery factor of less than 1%. The field development plan (FDP) identified the location of 20 new infill drilling wells targeting the sweet spots and considering the optimal well spacing. In addition, the plan specified a systematic hydraulic fracturing stimulation job for each newly drilled well to connect and produce the sand body lenses. Recently, a successful campaign of hydraulic fracturing operations was executed on four wells, allowing the operator to resume production from the field. The fracturing performance minimized water cut despite the water-oil-contact (WOC) proximity, and it enhanced the oil recovery.
The developed integrated approach has already shown its effectiveness in returning a field to production and improving oil recovery. The approach can be replicated on subsequent wells in the field as well as on similar tight reservoirs all over the world.