As operators plunge into deeper formations - many below 30,000 ft - ensuring hole size at total depth (TD) can be challenging. In the Gulf of Mexico, salt and sub-salt zones, pore pressure/frac gradient issues and over-pressured and depleted sands only add to the complexities and numerous drilling challenges.
Additionally, utilizing existing infrastructure to maximize capitalized assets is an attractive prospect. However, sidetracking or deepening out of an existing wellbore restrains inside diameter (ID).
This is where expandable technology becomes most beneficial.
SET® Technology Below 20,000 ft.
A perfect example illustrating the benefits of solid expandables is a well in the Gulf of Mexico shelf with a target depth below 20,000 ft. A sidetrack out of the 11-3/4 in. casing provided an optimal exit, but restricted options to keep the planned hole size at TD. By planning in a 7-5/8 x 9-5/8 in. expandable system, the operator extended the 9-5/8 in. shoe thereby adding the additional casing string needed. The well was completed with the proper ID to enable evaluation (discovering ~150 of pay). Not only was this the longest solid expandable installed to date at 6,935 ft, but it was also the first time swellable elastomers were used on the expandable system in the Gulf of Mexico (ensuring a successful leak-off test).
Another installation in a deepwater well provided assurance of reaching TD with the required ID. The well had been troublesome, requiring the 9-5/8 in. casing be set high. By installing a 7-5/8 x 9-5/8 in. expandable system, the operator was assured hole size for utilizing full-size logging tools. This particular installation is one of the deepest - the solid expandable shoe was set at nearly 30,000 ft.
Planning for Success
Because an expandable liner is often installed in challenging wellbores, the key to maximizing value lies in planning. In the two examples above, the operator and service provider partnered to ensure a successful installation in challenging wellbores. The first (shelf) well utilized the liner as a part of the wellbore architecture - reducing contingency costs and ensuring a successful installation. The second (deepwater) well planned the liner in as a contingency, thereby reducing the risk of not reaching TD with the required ID.
Future Systems, New Solutions
Enhancements to the standard expandable systems include high-performance technology which enhances the liner's burst and collapse ratings. This is especially important as operators push deeper into higher pressure and temperature regimes. For instance, an exploratory well might encounter unexpected formation pressure changes. Or a re-entry well may need to drill through a depleted zone with high differential pressures.
A high-performance expandable system recently installed provided a novel solution. An operator sidetracking through an existing wellbore had compromised 13-3/8 in. casing due to wear. The high-performance liner reinforced the weakened area, ensured pressure integrity and the operator's success in continued drilling.