Unconventional resources in Saudi Arabia symbolize an opportunity to extend required gas plateaus in the long term, to substitute gas for liquid fuels, and to provide potential feedstock for the growing chemical industry. This paper aims to outline an integrated completion engineering and geosciences approach that was applied in the Jafurah shale gas play. The goal was to address complex unconventional reservoirs and their associated challenges, and to determine the optimum completion and fracture design. Sweet spot identification within the Jurassic Tuwaiq Mountain Formation in the Jafurah basin represents a major challenge as it requires a large number of wells drilled over a wide geographical area with high associated costs. This requires innovative drilling, completion and stimulation practices. In order to identify and maximize potential frac stages and placements, a comprehensive study was completed using an advanced workflow encompassing drilling, geophysics, geomechanics, reservoir characterization, completion and fracturing and microseismic monitoring. The targeted Jurassic Tuwaiq Mountain rocks are calcareous and interpreted to have been deposited in a restricted marine environment within an intra-shelf basin. This shale carbonate play shows a high Total Organic Content (TOC), low clay content, good matrix permeability, high gas saturation and high effective porosity. Scanning Electron microscope (SEM) images exhibit a dominant presence of organic porosity associated with the kerogen. Initial results from vertical wells drilled in the Jafurah basin proved that proppant fracturing can be successfully placed, and indicated the presence of a potential gas rich play within the same source rock. Subsequent horizontal wells were the first liquid rich/gas carbonate horizontal wells with ultra-low shale permeability in Saudi Arabia. The first horizontal wells had excellent gas production with significant amounts of condensate. By further building on experience from the drilled and stimulated wells, the lessons learned provide a foundation for the completion of future unconventional gas wells in the Jafurah basin.
POGC Rehman-1 discovered gas from the Pab sandstone in mid-2009. The well had low productivity primarily due to low reservoir permeability. In December 2009, the well’s Upper and Lower Pab zones were fractured, resulting in a four-fold increase in production. Post-frac testing of the zones discovered very little proppant flowback. This paper outlines the history of this successful hydraulic fracturing treatment in the Kirthar region. The document also discusses the detailed job design, fracture modeling, pre-frac production model calibration, and sensitivities to treatment size. A series of fracture designs was developed to evaluate the uncertainty in fracture geometry predictions. The successful stimulation of a low-permeability gas reservoir dictated placing a long conductive fracture. An important aspect of fracture design is fluid selection. The fluid must maintain excellent proppant transport characteristics throughout the pumping sequence, yet break rapidly and cleanly once the treatment is completed. Another important aspect of fracture design: proppant selection. The proppant is basically the life of the fracture and should maintain adequate conductivity throughout the designed exploitation life of the fracture and completion. The fracturing program and the main treatment’s actual execution are presented in the paper. Operational issues are also discussed. One-hundred mesh sand was used to minimize the risks associated with pressure dependent leakoff (PDL) into natural hairline fractures seen on the FMI log. Post-fracture well-testing data was recorded and analyzed. The results were used to quantify the fracture effectiveness.
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