After suspending our operations in Azerbaijan in 2012, we are resuming our drilling program on the offshore Absheron Block with the stated goal of bringing this gas field onstream early – by 2020 – and at lower cost through a concurrent and dynamic appraisal of the reservoir extension with a view to future development phases. To meet that goal, it was decided to build a well with two “branches”, one for appraisal and one for development, which will eventually be tied into our partner SOCAR’s existing facilities.
Two wells in one
Located above a deeply-buried sandy reservoir, the operational zone features complex geology, which we had already encountered in 2011 when we drilled the ABX-2 exploration well (plugged and abandoned in early 2018). From that experience it made sense to opt for a two-in-one solution for drilling the high-pressure ABD-001 well to reduce the duration and hence the cost of achieving both appraisal and development objectives while also allowing to complete the well as early as possible.
Drilling began in May 2018 for a planned 379 days, thus shaving approximately 250-300 days off the time required to drill two separate wells (appraisal and development). Well ABD-001 consists of:
- An appraisal/downdip branch, targeting reservoirs Fasila B and D in the down-dip to the northeast to identify the fluids contact interfaces and better delineate the extent of the reservoir for subsequent development phases, down to approximately 7,500 m.
- A development/updip branch, kicking off from the existing well to the Fasila B and D reservoirs and drilled in the up-dip to the southwest, from a depth of 4,675 m down to approximately 6,900 m. This directional well will be optimized for condensate recovery.
Architecture of the highest complexity
Accordingly, the architecture of this well consists of no fewer than ten sections in the base case (when considering both branches), with extremely limited clearances and tolerances for the running of the various casings and liners.
To cross through a shallow pressurized “fizzy water” layer at approximately 900 m subsea, a dual gradient MRR (Mud Recovery without Riser) System was successfully utilized for drilling and for the subsequent 22-inch casing operations. The existence at approximately 3,000 m subsea of a barrier of poorly-consolidated creeping/flowing shale calls for rapid isolation to prevent inflows, loss of the drilling assembly and ensure the well’s structural stability.
In both branches of the well, variations in the reservoir pressure raise the risk of differential sticking of the drill string due to uneven pressure distribution around the drill pipe. To reduce this risk, specific mud properties are maintained and certain drilling techniques applied. In addition, for both branches the inclination is limited to approximately 30 ° to minimize this particular risk of differential sticking.
- The Caspian Sea is a landlocked body of water, and therefore there is a short supply in the number of rigs suitable for high-pressure drilling, available for a prolonged period, and able to operate to depths of 7,500 m. This constraint forced us to utilize a new build semi-submersible rig operated by a local rig contractor which we were not familiar with.
- With the project being fast-tracked, there was a tremendous amount of effort from the team to be ready for operations, including awarding as many as fifty new contracts and starting up a new logistics base ahead of equipment delivery.
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