Operators grappling with wellbore instability issues have sought to address them through a broad range of strategies. In conventional wellbore strengthening methods, for example, black powder and other lost circulation materials are added to the drilling fluid. Another approach is so-called ‘stress caging’, in which fractures are created and then sealed using specific concentrations of bridging agents. However, these tactics are typically reactive and often costly, requiring extra rig time and the management of multiple additives in the drilling fluid formulation.
Increasingly, operators are seeking ways to confront project-delaying wellbore instability problems before they occur. As this quest intensifies, an alternative, preventative approach – using Wellbore Shielding technology – was recently implemented for the first time in offshore Western Australia.
Wellbore Shielding technology is used in drilling fluids and spacer fluid systems where it generates a fast, effective seal, or ‘shield’, at the fluid-rock interface. This barrier against fluid and pressure invasion enables operators to successfully drill unstable, mechanically weak formations while mitigating losses. An important feature of this technology is its environmental compliance both in onshore and offshore environments. Wellbore Shielding technology has been used in producing fields around the globe, and most recently, in Australia.
Offshore Western Australia challenge
A major operator was planning a drilling campaign consisting of four gas and condensate wells in the Carnarvon Basin offshore Western Australia. Drilling engineers identified a significant risk of seepage loss and differential sticking in the lower part of the 12¼-in. intermediate sections due to high permeability. Additional challenges included high wellbore angles (up to 72 degrees) and elevated temperatures (139°C/282°F). These conditions put the operator’s advanced drilling tools, wellbore integrity and – ultimately – the entire campaign at risk. Adding to the complexity, any products deployed would have to meet the highest standards for ecological protection to fulfill the operator’s Environmental Agreement.
Wellbore shielding solution
Impact Fluid Solutions worked closely with the operator and a local university to conduct extensive testing on Wellbore Shielding products alongside other potential solutions, including commodity blends and specialty products from various drilling fluid companies. The team found that Wellbore Shielding technology offered superior sealing capabilities for pores and microfractures, quickly forming a strong barrier over simulated thief zones to minimise both fluid invasion and pressure transmission. In addition, while Wellbore Shielding products are available in a range of particle sizes, only one was needed to achieve the required seal – rather than a blend of multiple products – improving ease of management at the well site. Wellbore Shielding technology also offers greater convenience due to its low specific gravity (around 1.5 g/cm3 or 12.5 lb/gal). As a result, the products do not add significantly to the fluid density or equivalent circulating density, or affect the rheological properties of the drilling fluid.
Wellbore Shielding technology was added to the non-aqueous drilling fluid at the recommended concentration for approximately 200 metres (650 ft) prior to entering the troublesome zone. This was achieved by bleeding over a concentrated pre-mix into the active system while drilling was ongoing. Using API 80-100 shaker screens, the operator was able to minimise the loss of Wellbore Shielding additive over shakers while keeping low-gravity solids to an acceptable level (around 5 per cent).
Technology results
The operator reached section total depth (TD) in all four wells with no differential sticking events, mud losses or non-productive time, despite recording an overbalance of more than 2,000 psi (13,800 kPa). The deployment of Wellbore Shielding technology had no adverse effects on the operation, the functioning of downhole tools or surface equipment such as the solids control system and cuttings dryer.
Conclusion
Reactive approaches to wellbore instability issues can be extremely expensive for operators, driving up costs through fluid losses and additional rig time. Further complications may include sidetracks, unexploited reserves, loss of wellbores and—ultimately— abandoned wells. Now operators can implement field-proven preventative solutions such as Wellbore Shielding technology instead. These products protect the wellbore to prevent problems before they occur in the face of a broad range of drilling challenges.
