Incompetent shoe tracks are typical in oil well cementing and cost many hours of lost rig time for remediation. An incompetent shoe track results from unset, severely contaminated, or no cement inside the casing section between the float collar and shoe after a primary cement job. This paper will address several case studies where a systematic and engineered approach was utilized to apply various solutions that helped to improve the shoe track integrity.
The wet shoe has been of the utmost attention to oil and gas companies, as expensive remedial cementing operations are needed to repair the deficiency in shoe track integrity. After a thorough process review, many opportunities were identified to improve the cementing basis of design, such as lead and tail slurries for liners and multiple stage jobs, increased length of shoe track, the addition of bottom wiper plugs, and the use of lost circulation material in the spacer and cement slurries. This paper illustrates the case studies where the above-stated methods were successfully applied to improve the shoe track integrity.
Some of the major contributing factors to incompetent shoe track integrity were identified as attempting to cement the long sections with a single slurry, excessive thickening time requirements to accommodate the operation of liner hangers and stage tools, over-displacement of cement during placement, overestimated bottom hole temperatures, severe or total losses during cement placement, cement slurry contamination by the lack of a bottom wiper plug, and picking weak casing point. It was also observed that the consequences of poor shoe track integrity were amplified in challenging drilling environments where formations were either reactive, hard and abrasive, abnormally pressured, high downhole temperature, or prone to lost circulation. As a result, an increased effort was put in place to eliminate the poor shoe track integrity by implementing the opportunities identified during the process review. Cement inside the shoe track was found to take more weight on bit and have a slower penetration rate during drill out. Also, the required casing and formation integrity tests were achieved even in areas historically prone to compromised shoe track integrity. This confirmed the success of this systematic cementing approach and helped revise the basis of design.
This paper presents a detailed study of the novel engineering process that was successfully deployed to plan and execute the primary cement jobs with the assurance of shoe track integrity. In addition, this paper highlights the systematic approach utilized to eliminate or mitigate the occurrences of incompetent shoe track integrity with observed improvement in field deployment results.