Abstract

In recent years, a project was initiated to identify a safe and practical alternative to conventional silica-based cement slurries. The objective was to eliminate exposure to respirable crystalline silica (RCS) in oilfield cementing operations. RCS, as well as being linked to various respiratory illnesses (1), has now been identified as a human lung carcinogen (2), implying there is an established link between exposure to RCS and lung cancer.

When cementing well sections with a bottomhole static temperature (BHST) of over 110°C [230°F], a cement powder containing silica flour must be used to ensure the set cement matrix is stabilized to be able to withstand persistent exposure to these temperatures over time (mitigating against strength retrogression). A certain proportion of the silica within these conventional cement blends is classified as RCS.

The newly developed system, known as zero respirable crystalline silica blend or ‘ZRCS-blend’, was successfully applied on numerous occasions on a Norwegian rig. Interestingly, the system found successful application in a batch-drilled conductor campaign on a high-pressure/high-temperature (HPHT) field where the potential exposure during production exceeded 110°C [230°F]. Whilst being a safer alternative to conventional cement systems, the ZRCS-blend was able to deliver a top of cement (TOC) to the seabed on each and every occasion during the campaign, thus eliminating the need for any remedial operations.

As shown by proven success of the ZRCS-blend offshore on the Norwegian continental shelf, the system provides an alternative to silica-based cement for operations worldwide, to comply with regulations and health, safety, and environmental guidelines.

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