The production of wells in fields where thermal recovery techniques are in use, or will be in use in the future, is especially sensitive to the overall cement quality. Reliable evaluation of cement integrity is recognized as fundamental to the analysis of future production procedures or problems. Previous evaluation techniques have not fully addressed the parameters associated with thermal wells.
Recently, the cement quality in wells in the Celtic Tangleflags area of western Saskatchewan has been evaluated with two acoustic logging tools operating on sonic and ultrasonic frequencies, the objective being to optimize cementing procedures in the area. The refining of cementing techniques through the project has resulted in improved apparent cement quality, as indicated by the logging instruments. The benefits of improved cementing techniques will be discussed in light of the measurable results.
Some of the economic benefits of this procedure are outlined. Conclusions and recommendations for future work are given.
References and illustrations at end of paper.
Typical completion practices in the Celtic Tangleflags area of western Saskatchewan have resulted in poor predictability as to quality of cement bond and whether or not annular gas migration would occur. Although the wells studied are presently on primary production, buttress casing and thermal grade cements have been used to allow the operator the option of going to an enhanced recovery system in the future. Generally, all of the wells in this area are thermal candidates. Basic criteria for successful cementation would include the following:
no annular gas migration to surface,
adequate zonal isolation, and
uniform bond quality, and thus uniform casing support, throughout the well.
Figure 1 shows the location of the study area. Prior to this project, completion practices included the use of sonic and ultrasonic logging tools, but no correlation between cementing practices and logging results had been established. As a result, there remained significant potential for improvement in the cementation success ratio.
Concern by the principals involved regarding the effectiveness of the cementing procedures in use brought about a cooperative effort between the operator, the cementing company and the logging company to improve cementations in this area.
It was decided to complete a series of wells using the same monitoring methods. Despite the recognized difficulties in evaluating extended thermal cements, the sonic/ultrasonic logging suite provides the best data currently available for critical analysis. This suite allowed the operator to identify problem areas and to act to improve subsequent cementations. This program of monitoring and modification would continue only until an acceptable success ratio had been achieved.
This paper outlines the procedures followed throughout the project, including a brief discussion of cementing practices for thermal completions in this area, along with a discussion of logging theory and tool resolution in relation to lightweight thermal class cements.
This project successfully demonstrates that refinement of cementing practices (as indicated through the use of the sonic and ultrasonic logging tools) can result in significant improvements if the need is recognized and acted upon.