STUDY ON UPGRADING OF CONVENTIONAL CEMENT FOR ZONAL ISOLATION IN COALBED METHANE (CBM)WELLS BY USING FOAMEDCEMENT

Cementing gas wells in coalbed methane (CBM) formations can present a cementcirculation challenge because the coal formations tend to have low fracture gradients
and break down under the hydrostatic pressure of the cement column. The use of
conventional lightweight cement slurries and/or foam cement significantly increases
the prospectof maintaining circulation throughout cement placement. However, wells
with exceedingly low fracture gradients can suffer either partial or complete loss of
circulation during cement placement even with lightweight slurries. Both
conventional lightweight cement slurries and foam cements have restrictions.
Conventional lightweight cement systems use low-density materials (i.e. hollow
spheres, gilsonite) and high water-to-cement ratios as a means of reducing the
equivalent circulating density (ECD).