Saudi Arabia's Emerging Unconventional Carbonate Shale Resources: Moving to Horizontals with an Integrated Engineering and Geosciences Approach

Abstract

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.

The Effect of Hydraulic Fracture Geometry on Well Productivity in Shale Oil Plays with High Pore Pressure

“…From published data, we deduce that total fracturing fluid volumes and proppant mass per wellbore are about 18,000 m 3 (∼113,000 bbls) and 3600 tons (∼7.2 MM lbs) [44,45,47,81]. The average horizontal wellbore length in the Jafurah basin is approximately 1500 m (∼5000 ft) [45,53]. Some mudrock plays are further characterized by high pore pressure and a small difference between the principal stresses.…”

Workflow for Probabilistic Resource Estimation: Jafurah Basin Case Study (Saudi Arabia)

“…Closure pressure in the TWQ ranges between 0.98 and 1.05 psi/ft, based on DFITs [35]. The direction of the minimum regional stress is directed NNW, prompting for development with laterals extending in a NNW-SSE direction.…”