Breaking New Ground in Reservoir Management: Kuwait's First Underbalanced Coiled Tubing Drilling Operation for Blowout Relief in West Kuwait - A Global Success Story
Authors: Martinez Sebastian Sierra , Slama Mohamed Hedi , Alkhateeb Ali , Al-Dossary Ahmed Faisal , Chaari Youssef , Ali Al-Mayyan Haitham Ebrahim , Al-Mohailan Mohannad , Safar Emad , Al-Mutairi Bandar , Al-Ali Khalid Sami , Malik Abdullah , Baqer Hussein , Regaey Mohsen , Alajmi H. , Wiranata K. , Alenezi Saud , Harami Khalid , Alomar Abdulrahman Ahmad Abdullah , ElNaggar Omar , Al-Azmi Ali Abdullah Dhawi , Hasan Abdulmohsen Hasan Askar , Alzarnogi Rayan Ahmed , Sebaih Mohannad Adel , Al-Shehri Talal Ali , Ujagar Utsav , Pochetnyy Valentin , Armendariz Rocio Reyes , Baranov Sergey , Youssef Mohamed Nabil , Gia Toan Pham , Nazzal Tuleen , Mansour Waleed , Al Ali Khalid 
Published: November 2024

Abstract
Kuwait's shallow water-bearing reservoirs, traditionally drilled with diverters and large boreholes (28" and 22"), often face partial to total losses due to their highly fractured nature and low compressive strength. These shallow wells are crucial as water sources during drilling and workover operations. Recently, one formation communicated with deeper hydrocarbon reservoirs, causing uncontrolled surface leakage. This issue was partially managed using a diverter and surface lines to flare the surfaced gas, but this method posed risks of fractures behind the casing and uncontrolled gas surfacing. Given the unknown origin and position of the gas source, safely relieving pressure while identifying the cause is crucial. This paper documents the planning, implementation, and outcomes of Kuwait's first Underbalanced Coiled Tubing Drilling (UBCTD) campaign for relief wells. This innovative approach successfully addressed the challenges of conventional drilling, ensuring reservoir pressure control and preventing additional uncontrolled surface leakage and subsurface blowouts associated with the overbalanced nature of traditional drilling methods.
Upon establishing the target reservoir and its approximate area, the UBCTD team designed well profiles to ensure safe paths for directional drilling tools. A well integrity analysis determined the appropriate casing and tubing specifications to safely transport hydrocarbons to the surface and enable rig relocation. Finalized well designs underwent comprehensive drilling scenario simulations to evaluate the hydraulic impacts of underbalanced drilling on well productivity, drillability, hole cleaning, wellbore stability, and local formation strength, aiming to avoid borehole collapse and stuck pipe incidents. Specific H2S equipment and local procedures were implemented to ensure operational safety. A detailed hydrostatic pressure review was conducted to maintain a maximum of 160 psi at downhole conditions, aiding the targeted reservoir to flow towards the new deepened trajectory.
The first UBCTD campaign in Kuwait successfully drilled three shallow wells and an attempt on a fourth existing well, each with several laterals, safely channeling reservoir water and gas to the X-mass tree and production lines. The campaign addressed several uncertainties, including deepening and geo-steering with high dogleg severities in low compressive strength formations, borehole stability with underbalanced flow in medium to high inclination wells, and the impact of new wells on overall reservoir pressure.
This first global UBCTD implementation in Kuwait to relieve a blowout well demonstrated how high dogleg directional drilling systems, underbalanced drilling at shallow formations, a closed fluid system enabling simultaneous drilling and production, and the ability to move the rig without well shutdowns offer an optimal solution for drilling through charged reservoirs. The in-house makeup and construction of such a UBCTD package serve as a headline for operators facing similar drilling challenges, highlighting UBCTD as the optimal technique for complex environments.