Formation Testing While Drilling Enables Successful Pressure Data Acquisition in Depleted Reservoir Zone Not Previously Possible with Wireline Logging in Kuwait: A Success Story

Abstract

Formation testing while drilling (FTWD) proved to be of great value to the asset team at Kuwait Oil Company (KOC) while recently drilling a deep, deviated well to target the Zubair sands. The deviated 8-1/2-in. hole section of the well had been planned to cut through more than 1,100 ft of true vertical thickness containing multiple reservoir units with varying pressures, lithologies, and formation characteristics, which posed a great risk for drilling operations and required the use of relatively high-density mud to maintain wellbore stability. The presence of highly depleted reservoir zones in this mature reservoir resulted in a challenging pressure overbalance in excess of 4,800 psi. Attempts to measure formation pressure in previous vertical offset wells in the same depleted zone in the same field/environment using wireline formation testers yielded either unsuccessful or erroneous results, indicating a tight formation, which conflicted with previous production and coring data available that suggested high-permeability sands were present. The high overbalance was suspected to be the primary cause of formation damage and blockage resulting from solids content in the drilling fluid and longer exposure time. KOC has historically opted for taking pressure points in wipe mode rather than dynamically while drilling in open holes containing unstable Zubair shales. Moreover, a large number of planned pressure points with the drilling assembly cutting across various sand zones posed several challenges. The asset team had plans to exploit such depleted zones through future horizontal drilling; however, an up-to-date pressure measurement was required to assess feasibility. This paper discusses the planning, design, and execution of this well. It also focuses on the use of the FTWD solution alongside other logging-while-drilling (LWD) and rotary steerable assemblies to overcome the drilling challenges and successfully follow the planned data-acquisition program to optimize the completion and production strategy and discusses how the solution affected the decision making for future wells.