While using conventional surface launch cementing plugs during cementing operations performed on large diameter surface pipe, significant costs are incurred during the pumping of cement and displacement fluids because of the large volumes involved in the job. Additionally, high differential lifting pressures sometimes exceed the safe collapse load that can be applied to the large casing; thereby preventing the operator from checking the float valves after displacement is complete.
For several operational reasons, the operator elected to cement subsequently installed surface pipe using the inner-string method of displacement.
To help reduce overall job execution time and provide safer means of checking the floats after displacement is complete, a versatile surface packoff was incorporated into cementing operations on many large-diameter surface jobs. The time required to run the work string and install the surface packoff was easily justified with reduced costs associated with actual job execution. This paper documents the operators cost analysis along with operational benefits realized from the use of inner-string cementing and surface packoff methods.