Published on 28 June 2022
Casing patch relines worn sections to enable sidetrack.
Four patches successfully repair significant casing wear in overlap and restore the casing integrity to allow resuming sidetrack drilling operations.
Casing integrity is critical in drilling operations to re-enter and successfully sidetrack an old well. Working in a brownfield is full of surprises, which involves using versatile and reliable tools to fix integrity problems when they occur. The current case study below describes the successful installation in an overlap of four expandable steel patches to cover severely worn casing sections. The patch intervention sought to restore the casing integrity and enable resuming the sidetrack drilling operation.
The loss of integrity prevented the sidetrack operations.
A failing pressure test indicated a leak in the production casing. A multi-finger caliper run identified severe longitudinal casing wear from 1,699ft to 2,362ft [518m to 720m], more likely due to the localized high dogleg, with fully penetrating holes at 2204ft, 1,801ft, and 1,745ft [672m, 549m, and 532m] depths. The high dogleg did not help prevent the consequences of continued rotation while RIH of the drilling string against the casing wall in the deviated section. The repeated rotation of the string contributed to damaging the casing wall during the drilling. Casing wear is a considerable risk in deviated wells. Centralization is not always sufficient to avoid or mitigate any risk of damaging the casing while running in and rotating. The lack of casing integrity prevented the scheduled sidetrack operations from being carried on.
Unsuccessful cement squeeze jobs
Numerous attempts were performed to squeeze the worn casing section with remedial cement jobs. They all revealed unsuccessful. In other words, Schlumberger asked a second caliper to check if the cement squeeze jobs had helped reinforce the area. Surprisingly the zone appeared to be even more damaged, with a complete casing breach. The planned solution seemed impossible to implement and presented a high risk of failure.
The mechanical repair was the last option
The mechanical repair was the last remaining option to save the well. From the initial caliper log, Schlumberger designed a solution to cover the long interval with four customized casing patches of 13m. The products were manufactured while the operator moved to the other wells of the program.
At that time, the planned solution looked impossible to implement with a high risk of failure.
Further examination and cooperative engineering led to completely redesigning the solution. It involved changing both the length and position of the patches and scheduling one of the patches as an inner reinforcement to a previously installed outer patch (See the scheme at the right, Patch#4 in Patch#3). The final design (as described on the bottom page in the new patch placement) included four expandable steel patches: 15.6m + 15.6m + 8.2m + 15.6m, instead of 4*13m in the initial patch placement.
The patch installation
The objective of installing the casing patches was to re-instate intermediate casing integrity to allow a secondary barrier when drilling the 8-1/2” hole. A casing pressure test of 650psi was required. Note: Minimum secondary barrier requirement to contain and circulate out a 25bbl kick given kick intensity of 0.12sg (1ppg). Also, a minimum ID of 8.60” was required to allow for an 8-1/2” Drill Bit to resume normal operations. The client had set the whipstock before installing the casing patch due to the ID limitation of the casing patch.
See also ‘casing repair techniques‘