Highly depleted zones could represent a major challenge for well completion or intervention because of several issues, including high losses, crossflow, and low fracturing pressure. However, nowadays, there are several options to treat or isolate depleted zones to allow further well completion or intervention.
A major North Sea operator had plans to perforate in Formations B and C formation on a well after determining that they could still be at original pressure and separated from the already producing and depleted Formation A. Following a second perforation run on wireline, tool lift was measured. This tool lift correlated with crossflow from the newly perforated zone to the existing depleted A zone, and did not allow the perforation guns to reach the required total depth (TD).
The service company proposed a three-dimensional rigid gel system comprised of an organically crosslinked polymer (OCP) conformance sealant with particulates. The system, deployed with coiled tubing (CT), was designed to be squeezed into the near-wellbore matrix. The depth of penetration is controlled by adjusting the particulates concentration in the gel system and squeeze volumes. Fluid volumes were calculated to achieve 6 in. of formation penetration. Laboratory tests suggested that the polymer would cure after 12 hours at bottomhole static temperature (BHST) and excess in the wellbore could be jetted out using CT.
A total of 30 bbl of gel system were pumped in two separate batches, with partial isolation and reduction in fluid loss achieved after the first 20-bbl batch. An additional 10-bbl batch was pumped to help ensure isolation. Pressure tests and fluid loss after the second treatment indicated almost 90% of the open perforations in the depleted zone were isolated with minor losses observed compared to a loss of more than 80% in the wellbore before the treatment. The operator was satisfied with the results and, after jetting the excess gel from the wellbore, perforation operations were performed successfully.
This paper discusses in detail the job execution, including CT and pumping equipment which were selected specifically for this operation, and including cleaning and pumping, bottomhole assemblies, running in hole procedures, the pumping schedule; fluid recipe used, and laboratory testing performed to define curing time and rheology.
This paper also highlights challenges faced during execution caused by high depletion, techniques used to overcome these challenges, and methods used to evaluate the success of the isolation while CT is still in hole.