Abstract

A 1575m [4922-ft] offshore horizontal 4-½-in. liner cemented using a mud-sealing cement system (MSCS) resulted in an outstanding cement bond log result. The decision to use the MSCS was taken after realizing that four offset liners, previously cemented using conventional cement systems, did not yield acceptable cement bond log results despite following oil and gas cementing industry best practices, including pipe rotation. This paper documents a comparison of six offset horizontal liners, focusing on the impact of the MSCS technology.

The paper focuses on several 4-½-in. liners in the same field. The wells were drilled by a similar rig and had similar well profiles. The drilling bit, directional drilling tool, drilling fluids system, logging tool, centralizer type and pumping sequences were comparable across all wells. In addition, the logging company performing the cement bond log evaluation was not the same company performing the cementing service. After the first MSCS-cemented well, the subsequent well used a conventional cement system to isolate the 4-½-in. liner and tighten the cementing best practices. This was initiated to irrefutably confirm the impact of MSCS technology on the quality of cement bond log recorded on the earlier well.

The cement bond log recorded from the well isolated with MSCS is easily identified among the six comparison wells even though the cementing operation faced several well challenges, including

  • a single dart liner system implementation (for all liners), which can promote the intermixing of slurry with fluid ahead while travelling down the pipe

  • mud losses in the drilling phase, which resulted in a reduction of the displacement rate to control ECD during cement placement.

The bond log results of the other wells were qualified as poor or fair, even though significant precautions were taken to optimize zonal isolation. These efforts included batch mixing the spacer and slurry, using more than one centralizer per casing joint, and implementing pipe rotation during pre-job circulation and job execution when the torque limit allowed.

This multi-well comparison based on field results brings solid evidence of the MSCS technology interacting with the residual layer of nonaqueous fluid (NAF) when well conditions reach or exceed the practical normative limitations for mud removal. This in-situ interaction generates a viscous paste that positively impacts the bond log response and bolsters the isolation between zones of interest. The result has yielded a step forward in the provision of a dedicated barrier technology for horizontal or highly deviated sections.

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