Achieving long term well integrity in deep gas wells offshore Abu Dhabi has presented some unique challenges. Historically, cases of poor zonal isolations has led to pressures in annuli and even sea-bed seepages. In one case this had caused well-head movement, causing concerns about the integrity of well-head platforms and surface equipment. Corrective actions to remedy failures has cost the operator millions of dollars in addition to taking up valuable resources and rig-time.
The challenges were to ensure proper zonal isolations in these deep gas wells, where several stacked reservoirs have to be drilled prior to the target Khuff reservoir. Well-bore instability in shale formations and lost circulations into weaker, fractured carbonates presented significant complications, which seriously impacted the efforts of achieving zonal isolations in the multiple reservoirs. Thus, an integrated approach was undertaken to overcome these challenges. This encompassed well and casing design, drilling fluids formulations, cement designs, fit-for-purpose equipment, in addition to maintaining a stable well-bore and addressing the loss circulation issues that effectively raised the fracture gradients of weaker formations. The paper provides an overview of the optimization processes involved in the successful planning and execution of the wells.
The paper describes the development and application of drilling fluids for different hole sections to achieve well-bore stability as well as mitigation of lost circulation incidents. The particular fluids technique used to strengthen the weaker formations resulted in the ability to place the cement slurries in the well-bore as designed. As described in the case histories, the adaptation and application of various fluid technologies to arrive at fit-for-purpose solutions and the engineering of the total integrated drilling and cementing fluids solution was crucial in achieving the necessary zonal isolations to ensure long-term well integrity of the gas producer and injector wells.