Borehole Imaging of Natural Fractures and Stress Indicators in the Jurassic Carbonate Shale Plays, Eastern Saudi Arabia

Summary An operational geomechanics study has been underway to facilitate the unconventional exploration and appraisal of the Jurassic carbonate shale (mudstone) pay zones of Eastern Saudi Arabia. Part of the study involved the multi-scale imaging of natural fractures and stress indicators. Natural fractures are mainly of microscopic and mesocopic scale (individual fracture length ≤ several ft). No major faults occur in any of the tens of imaged long reach horizontal wells, and the imaged and cored vertical wells. Therefore, the natural fractures facilitate hydrofracturing. The absence of major fault zones or fracture clusters reduces the risk of pressure and fluid thieves during hydrofracturing, and minimizes potential damage associated with fracture hits. The natural fractures and current day stress regime is persistent regionally, and has been actively driven by the Late Cretaceous to present Arabian Plate tectonics. The current day stresses within the pay zones are characteristic of thrust to strike slip tectonics with the maximum horizontal in-situ stress trending ENE-WSW parallel to the current day Zagros stresses. These regional stress and fracture patterns facilitate well planning, completion and stimulation design with horizontal wells designed perpendicular to the maximum horizontal in situ stress.