Immobilized enzymes: a comprehensive review

Background This article is a comprehensive review of the events recorded in the history of enzymology from twentieth century to the recent work of author’s groups on different biochemical aspects of the immobilized enzymes. The review differs from those presented before on the basis that it is not limited to one or few aspects. It extends its spectrum to a large number of aspects from the definition to biomedical applications of immobilized enzymes. Main body The author and his associates have proposed modification of classification of immobilized enzymes by Enzyme Engineering Conference 1971. His groups have worked on cell bound proteases of medicinal seeds and have given them the name of “naturally immobilized enzymes”. Thus, the author proposes that the enzymes may be basically classified into “naturally immobilized enzymes” and “artificially immobilized enzymes”. The artificially immobilized enzymes may be further sub-classified as done in 1971. Conclusion The classification suggested above sounds logical and thus acceptable to the author and his associates. The author and his associates also suggest some applications on the basis of their results on naturally immobilized enzymes.

Rotating Cement Heads Improve Results of Zonal Isolation in Colombia

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 198970, “Casing Rotating Cement Heads: A Custom-Fit Solution To Improve Zonal Isolation Results In Colombia—A Field-Proven Case,” by Jose Vela, SPE, Henry Arias, and Edwin Sanchez, Ecopetrol, prepared for the 2020 SPE Latin American and Caribbean Petroleum Engineering Conference, held virtually 27–31 July. The paper has not been peer reviewed. In the current challenging drilling environment, effective annular zonal isolation is required for long-term integrity. Among proven cementing practices, casing rotation has been widely applied to liners but not as commonly to full casing strings. The complete paper describes the use of custom-fit rotating cement heads (RCH) to improve cementing results. Cementing Practices in Colombia The following methods of cementing, described in detail in the complete paper, are applied currently in Colombia: - Preflushes and spacers - Slurry design - Casing standoff - Borehole conditioning - Mud circulation and conditioning - Casing movement during the cement job - Monitor job parameters compared with design - Pressure testing and surface-equipment installation Most of these best cementing practices have been followed on a daily basis for all production and intermediate casing. Rotation practice has been widely applied to liners but not for casing strings. This observation led to the introduction of RCH, a technology that arose as the most- appropriate link to connect the top drive or rig prime mover with the casing so that rotation for a full string of casing could be achieved. RCH Use and Implementation Before the implementation of RCH, cement evaluation logs did not show the expected response. Evidence of fluid channeling and fluid contamination was very common, and fair casing to cement bonds was a concern, particularly in washed-out sections and very long cement columns. RCH provides a technical solution for the need to rotate the casing strings while maintaining best practices common to all cement jobs. Rotation has shown to be mandatory for intermediate and production casing to obtain a better log response by enhancing displacement fluid efficiency and mud removal. Well-design and cement objectives vary according to regional sedimentary basins around the country. In the Llanos Basin, the intermediate casing shoe integrity and the isolation of the T1 sand unit are primary objectives; the most-common wellbore problems are the presence of very washed-out sections in front of the E3 and E4 shale formations. The T1 sand unit is located between them and is prone to water or gas influx. Next, the production section is drilled with a lighter mud so that a high negative differential pressure is induced around the casing shoe once the shoe track is drilled. If shoe integrity is not suitable, an influx can be promoted when drilling the productive zone.