Overcoming Cased Hole Logging Challenges to Assess Waterflood Conformance in Clair Ridge Segment 2B

Clair Ridge is the second phase of the Clair area development situated west of the Shetland Islands in the North Sea. The Devonian sandstone reservoir is relatively tight (around 10 md on average) and contains a relatively viscous 24 API oil that provides low oil flow rates unless the natural fracture network within the rock can be exploited for productivity and injectivity. Pressure support and oil sweep are achieved through LoSal (reduced salinity) injection, enabling recovery through a combination of viscous drive, gravity drainage, and imbibition, with the reduced salinity also limiting H2S development. Long horizontal openhole wells are drilled to facilitate access to natural fractures. Each reservoir section is completed with a liner, swell packers for annular isolation, and timer inflow control valves (ICVs) to facilitate sequential startup. Communication between the liner and sandface is often limited to two to three ports per reservoir zone. While this completion style is necessary for a successful well, it does pose a challenge for cased-hole (CH) data acquisition as there is no direct access to the sandface. B16 (injector) and B15 (producer) are an injector-producer pair within segment 2B of the Clair ridge field. Good injector conformance was vital to oil recovery within the segment. Injection into each reservoir segment can be controlled using the ICVs (open/closed), but first, the well performance and swell packer integrity need to be confirmed using in-well surveillance. Since the completion allows no direct access to the sandface, the team needed to get creative with logging techniques. An all-in-one logging string was used to assess flow diagnostics per reservoir zones, flow diagnostics at the sandface, three-phase matrix saturation, and swell packer integrity. The data were assessed in real time to allow for adjustments to downhole flow control. The string included traditional production logging tools, a pulsed-neutron tool, and passive acoustic tools to achieve these goals. A combination of CH interpretation techniques was used to understand well performance, well integrity, and matrix sweep. These included traditional production log analysis, water flow logging using oxygen activation, nuclear attribute response, acoustic analysis, and warm back analysis. The team also took one step further to integrate this data with the image logs, fracture presence, completion design, and well startup. The CH surveillance data indicated that good injectivity conformance into the segment had been established and that no adjustments to the downhole flow control were required. The team was able to achieve insight into injectivity at the sandface and matrix sweep and confirm swell packer integrity. The surveillance also confirmed that the well startup methodology was successful in establishing conformance along a horizontal well with varying fracture intensity.