Abstract
Chemical and physical modification of a sustainable, derivatized-cellulose polymer has created a single material capable of replacing several different cement additives. This slowly-hydrating, hydrophilic biopolymer is capable of performing as a fluid loss agent, suspending agent, free water control agent, and extender for use in wells up to 225°F and in some conditions up to 250 °F.
The single, new cement additive effectively and economically replaces separate fluid loss additives, free water control, and slurry stabilizers as well as reduces retarder loadings. Laboratory and field results, operational aspects, and slurry design simplification are conferred in this publication. Standard API test results using Class H ordinary Portland cement slurries with densities ranging from 13.5 ppg to 15.5 ppg including a 14.5 ppg cement blend containing 50% fly ash at multiple temperatures are presented.
The biopolymer works best with the lower and middle density cements. Unlike most fluid loss polymers, this new additive doesn't produce the high initial viscosities, thereby reducing pumping horsepower requirements and equipment wear and tear. A field case in an 18,000 ft horizontal well (8k ft vertical, 10k ft horizontal) confirms the polymer's effectiveness. Preventing fluid loss is critical in maintaining the proper amount of water to give the cement proper density and mechanical properties. Without adequate suspension and free water control, cement particles will settle at the bottom of the slurry resulting in poor zonal isolation. Slurries containing the cellulose biopolymer performed equal to or better than slurries containing multiple, traditional additives. These additives can interact with each other both antagonistically and cooperatively so that a minor change in one can cause unwanted ripple effects to the slurry properties. This makes slurry design complicated and time-consuming. Replacing several of the commonly-used additives with this modified cellulose minimizes and even removes these complicating ripple effects.
The polymer's ability to serve different roles at the same time leads to smaller additive inventories, easier logistics, less time spent on slurry design iterations, and simplified field operations which all add up to improved economics and reduced chance of error during placement of the cement.
