Abstract
Remedial operations on high permeable und underbalanced reservoirs can become risky. Lack of an exact liquid level, tight clearances leading to a high ECD and old unreliable reservoir characteristics can result in a fast liquid loss situation occurring out of view. Good mud properties can handle this issue but an instable filter cake can quickly lead to a situation where the formation will be filled with cement while your secondary liner is still uncemented. This situation is irreversible and in the worst case may even stay unnoticed.
Casing patches, which are thin steel liners tightly pressed against the inside wall of a casing and designed for zonal isolation and casing leak treatment, can be an efficient remedy for these type of problems. Used on perforated reservoirs they provide a stable and reliable temporary barrier during a workover. The reservoir is reopened using conventional perforating guns once the workover is finished. Since the patches are non-invasive, no additional reservoir damage can be expected.
Within the fields of GDF SUEZ Germany Exploration & Production (DExPro) this technique has been used successfully on three wells in 2011. Two of these wells required a secondary liner and one needed to be hydraulically fractured in order to overcome strong reservoir damage. All three had significant issues that made a conventional workover approach risky. The casing patch technology provided reduced contingency in the workover plan and provided an excellent protection of the fragile reservoir environment.
