Critical Success Factors Identification to Develop Unconventional High Porosity Low Permeability Shallow Limestone Reservoir of Apollonia Formation, Western Desert, Egypt

摘要

The Apollonia reservoir is one of the unconventional highly porous and low permeability gas opportunities in Egypt that was not previously properly studied and is currently being appraised by Shell/BAPETCO. The characterization and evaluation of the Apollonia carbonate reservoir in well BED 9–3, of BED 9 field, Western Desert, Egypt was accomplished by integrating a multi-disciplinary dataset with production data to ultimately approach the key controlling indicators for future Apollonia reservoir development plans. Critical success factors for the Apollonia reservoir development in the BED 9 field are identified and assessed by using/integrating the openhole dataset (including triple combo, borehole micro-resistivity imaging data, mineralogical data, and nuclear magnetic resonance data). This information is calibrated with core data analysis, X-ray diffraction (XRD), and petrography analysis. This study was performed throughout three primary disciplines: geological interpretation (depositional rock fabric and textural analysis, fracture analysis, diagenetic processes, pore system identification and classification, and clay typing and its effect on reservoir quality), petrophysical evaluation (fluid typing, distinguishing moveable from immovable water, and hydrocarbon saturation), and production performance data. The Apollonia formation grades from clean chalky limestone to marl with occasional mudstone streaks, expanding on the lithofacies identification. The petrographic analysis shows that the Apollonia carbonates are generally classified as a mud-supported texture that commonly ranged between wackstone to mudstone; it also shows that reservoir properties are dominantly influenced by depositional processes, in accordance with the clearly identified original rock fabric and bioclasts with little diagenetic and fracturing influences. The pore system identification and classification shows that porosity is generally high with very poor connectivity (low permeability) in which the majority of pore spaces are microporous. The formation includes considerable amounts of smectite, kaolinite, and illite, generally identified using XRD analysis and scanning electron microscope (SEM) analysis that affect porosity and permeability. Extending the geological and petrophysical evaluation performed over the Apollonia formation, neither natural flow nor small scale fracture jobs were efficient enough to provide for commercial production rates; consequently, BAPETCO has performed large scale foam fracturing operations to maximize the well productivity and to improve the project economics. These fracture operations were considered to be the first successful implementations of foam fracturing in North Africa, as well as the second largest ever in terms of proppant volume. The well showed a significant improvement in productivity of more than 40 fold after the treatment. The Apollonia reservoirs in the BED 9–3 well were produced at a commercial and sustainable rate, after the reservoir properties were understood, using the optimum/convenient production job design. The fracturing work is considered to be required as a critical success factor for the Apollonia reservoir.