Use of Water Base Spacer with Thixotropic Cement Systems Improves Cement Jobs

Abstract

Abstract Cementing has been improved by application of a new water-base spacer ahead of thixotropic cement systems. Weight differential between the spacer and drilling mud can be easily controlled to provide good mud removal. The spacer helps control water loss of the following cement thus permitting use of a thixotropic system with expansive and proper rheological properties. Both bond logs proper rheological properties. Both bond logs and stimulation results have confirmed better cementing jobs using this new cementing technique. Introduction Past field Experience and laboratory studies have led to the identification of several factors which contribute to better cement jobs. Some of these factors are: use of a spacer to separate mud and cement, use of a low fluid loss cement system, and use of a cement that expands. In many areas, it has also been found desirable to use a thixotropic cement. In the past it has seldom been possible to make use of all these factors in a single application. For example, known fluid loss additives could not be used with thixotropic cements since they dispersed the systems. Repeated failure to find a fluid loss additive for the thixotropic systems led to a new approach to this problem. It was decided to develop a spacer which would lay down a filter cake to control the fluid loss of the cement that followed it. In addition to providing fluid loss control for the cement, such a spacer would have to meet other requirements. Some of these are:It should be compatible with drilling muds.It should be compatible with the cement systems.It should have low fluid loss.It should be a water-base material, rather than oil, to facilitate disposal. Such a spacer has been developed. For the purpose of simplicity, it will be referred to purpose of simplicity, it will be referred to as WBS (water-base spacer) in this paper. WATER BASE SPACER The water-base spacer consists of gelling agents and fluid loss additives. Actual development, however, required extensive research. The most difficult phase was finding the proper fluid loss additive.