Effects of storage upon the cementing properties of Class G oilwell cement plus 8% bentonite blends
- BP International Ltd., Middlesex (United Kingdom). Sunbury Research Centre
G + 8% blends of bentonite were similarly stored for up to 1 1 weeks. Blue Circle Class G cement was used for these investigations. Two beneficiated bentonites and two natural Wyoming bentonites were employed. Operating free fluid (free water) tests (API Schedule 5) showed that free fluid (free water) for the G + 8% blends tended to increase with storage time. The blend with beneficiated bentonite was particularly bad in this respect, giving much higher and rising free water contents with increased storage time. Thickening time data performed up to 2 weeks storage backed up this data. The longest Schedule 5 thickening times were obtained with the G + 8% bentonite 1 blend. Increases in free water and thickening time with length of storage of the four G + 8% bentonite blends can be attributed to increased aeration (exposure) of the cement from the bentonite moisture. There was no correlation between bentonite moisture content and the development of high free water values or longer thickening times. Indeed the lowest moisture content of the four bentonites was that of the beneficiated bentonite. Thermal analysis data suggested that the particularly poor results of the G + 8% bentonite 1 blend was due to poor performance of this impure bentonite. In this particular instance there was most likely a breakdown of the beneficiating polymers with length of storage by alkaline hydrolysis in the cementitious medium as a result of increasing aeration (exposure to moist air) with storage time. It is necessary to recommend that when bentonite be used in G + 8% blends, quality control be carried out on the blends for appropriate operating free water and thickening time. API Specification 10A tests for bentonite are mostly irrelevant for quality control in these circumstances.
- OSTI ID:
- 7207918
- Journal Information:
- Cement and Concrete Research; (United States), Vol. 24:2; ISSN 0008-8846
- Country of Publication:
- United States
- Language:
- English
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