Geosteering and Challenges of World's Longest Top 3 Horizontal Wells in Tight Carbonate Reservoir and its Benefits
Authors: Mohamed E. A. , Alyan M. , Jamal F. , Alhashmi M. , Hassan N. A. , Alqaydi N. , Alnayadi K. , Pace D. , Aljabri S. , Al Noukhatha J. , Alsuwaidi N. 
Published: November 2024

The paper describes the Geosteering methodology to optimize the well placement and performance of ultra-long maximum reservoir contact (MRC) laterals while reducing the drilling risks and costs and enhancing long term reservoir recovery and management. The case study details the Geosteering techniques and challenges involved in drilling the world's longest top 3 horizontal wells exceeding 50,000 ft total depth.

Geosteering ultra-long horizontal wells – in a target carbonate layer of 4-20 ft. in thickness is challenging especially with very limited geologic data. The well design process starts from planning a 3D well trajectory to meet the defined reservoir landing and total depth points as per the development plan. Then by utilizing the structural geologic model which includes input data from seismic and nearby wells, the well design is adjusted within target layer. For the execution phase, planned logging-while-drilling (LWD) tools are deployed along with measurement-while-drilling (MWD) to make real-time modifications during Geosteering for drilling the ultra-long lateral. Additionally, the well Geosteering process accounts for anticipated drilling challenges and uncertainties associated with petrophysical analysis to meet field development set objectives.

Horizontal lateral was drilled to the target total depth successfully. Before execution, drilling torque and LWD telemetry were expected to be the most likely limiters for achieving the well plan. For maximizing chance of success, it was critical to find the torque sweet spot inside the target layer and avoid scratching any stylolite formations while drilling the 8½-in hole section. Therefore, Geosteering flexibility in well placement has led to minimizing cumulative doglegs and avoiding significant torque swings which lead to exceeding torque limits and drill string failure.

In terms of dealing with data transmission at higher depths, downlink and signal telemetry settings were optimized to avoid excessive troubleshooting. Additionally, LWD tools were set up to maximize priority data for successful Geosteering which is directional density image and resistivity. In case of reduced or lost signal, the bottom 30 ft. interval of the stand was re-logged for Geosteering ahead. Additionally, effective Geosteering protocol between geologists and directional drilling led to achieving target even when angle control of rotary steerable system was lost. Post-drilling analysis of LWD data shows good agreement with geologic model.

Subject wells are the longest worldwide with more than 50,000 ft. depth and are the longest single laterals drilled in UAE with more than 33,500 ft. reservoir interval. Valuable reservoir properties such as porosity and saturation were obtained till TD for reducing uncertainty and de-risking future well planning. Moreover, the strategy of extending horizontal laterals led to a more sustainable way of development by reducing footprint required and maximizing captured oil reserves per well through reducing development wells count.