The practice of deep-well drilling (i.e., reaching depths of 15,000 ft or more) has been increasing for more than three decades with well costs increasing as record depths are continually challenged. The demand for gas has generally supported this drilling activity, nevertheless the pursuit for drilling the most economical well continues. This paper presents a case history of cementing a long, intermediate casing string. Such casing strings are strategically placed covering a large section of the drilled hole straddling as close as possible between the lowest fracture gradient and the highest pore pressure in the drilled section. Such a design helps minimize the number of casing strings required for the well, thus helping to reduce the well cost. While it might be possible to drill the hole by maintaining a balancing act between flow and loss situations, the cementing challenges remain to be tackled.
The use of foamed cementing has addressed the issue of cementing in a lost-circulation situation and controlling the flow from a gas zone found within the same interval. When compared to conventional cement jobs, foamed cement was not only superior in technical design but provided several cost-saving benefits that many potential users might be unaware of. For example, the bulk cement-volume requirement dropped by a factor of 1.72, provided a cost saving of approximately 35 to 40%, and reduced the bulk equipment footprint from 1,560 ft2 to 936 ft2. The job-time also decreased by three hours. These discrete savings combined are significant.
Though this solution brings much benefit to operators, it is still regarded as an unconventional cementing solution. This paper provides a case history, economic analysis, physical properties, and developmental background of foamed cementing that should help operators see its benefit and use.