The CBM process is an amalgam of oilfield and coal-mining practices that have merged and often require the investigation of parameters that were previously ignored. Production of coal bed methane (CBM) in a short time has become an important industry, providing an abundant, clean-burning fuel in an age when concerns about pollution and fuel shortages preoccupy the thoughts of many Indians.
This paper excerpts the successful use of high strength & low density cement slurry used for primary and remedial cementing jobs in Coal Bed Methane wells in the Raniganj block of Eastern India.
Cement is placed as a sheath across coal seams in coal bed methane wells primarily for hydraulic isolation and to support the casing. Designing a cement job for coal seam wells requires contemplating factors beyond those considered in cementing conventional oil & gas wells.
The successful cementing job in coal seams faces several challenges, viz. cement invasion into coal seams, losses during jobs, low fracture gradient and low formation temperature. Since, most of the CBM wells need to fracture the cement sheath between casing and formation, thus the set cement should not only have high compressive strength, but high tensile strength as well.
The unique advantages of high strength & low density cement slurries are:
Reduced density to take care of low fracture gradient of coal seams.
Prevent invasion and loss circulation.
Eliminate the need for stage cementing.
High compressive strength.
The paper also explains the importance of flush-type spacer for better hole cleaning. It is also be used to cure loss circulation zones.
This paper shares case histories and best practices developed for successful cementing operations in CBM wells; and experience of designing, simulating and real time data acquisition.
With the application of real time data acquisition, downhole ECDs (equivalent circulating densities) of fluids can be monitored and kept in check.