Challenges on Well Placement in Thin Layers Targets in Central Oman, Rub Al Khali Basin

Abstract This paper highlights two successful cases of horizontal drilling, emphasizing the critical importance of precise and accurate development of these thin sweet spots. Geosteering has become essential for optimal well placement, especially in reservoirs where the target horizon can be as narrow as 1 meter, requiring placement within the top 0.5 meters of the reservoir. The cases discussed in this paper exemplify effective placement in two fields within a challenging Ordovician reservoir (clastic environment). The success of these placements was achieved through a combination of geosteering strategies, azimuthal measurements to determine proximity to the roof, and close monitoring using a robust software platform for real-time well positioning and field data, including oil and gas show indications. Data from azimuthal resistivities and triple combo from LWD were extensively utilized to avoid roof scratching and loss of the drilled hole. This data was effectively managed using specialized geosteering software, which helped identify roof proximity and supported decision-making in the directional drilling process, thereby increasing the contacted pay zone and maximizing expected production from the wells. The two cases had distinct objectives. The first case involved recovering a previously collapsed hole lost five years ago after penetrating the roof and intersecting the shales above. Production in the well ceased abruptly, and the deferred production due to the collapsed hole justified a new sidetrack. The previous well intersected only 150 meters of pay, with 100 meters into the shale. The new well achieved 605 meters of continuous pay zone, significantly impacting production. The second case involved a new horizontal well with a challenging trajectory due to wellbore stability issues during landing. This required constructing a 3D trajectory, changing azimuth along the path, avoiding severe dogleg changes, and maintaining steerability within the target zone. The well intersected a total of 973 meters of pay zone, confirming good oil saturation through the contacted sandstone interval. The final output from this well significantly increased field production and opened new opportunities in one of Oman’s lesser-known reservoirs. Without the proper combination of tools, software, data, and skilled professionals, placing wells in these difficult targets would be nearly impossible. Poor placement results in disappointing outcomes and additional costs for the operator, including sidetracks, deferred production, and undeveloped reserves.