This paper presents a new process for development of a novel cementing composition to provide ductility and thermal stability to the cement sheath in thermal recovery wells subjected to high temperature cycling during ISC process. In this novel composition a carbon-containing natural mineral fiber and an aluminum silicate additive are introduced along with Portland cement to perform effectively in wellbores having conditions prone to stress-induced cement failure.
ONGC's heavy crude oil-fields in north Gujarat, India necessitate the inroduction of thermal recovery process for improving the oil recovery. However the durability of the cement sheath consisting of API Class G cement admixed with silica is endangering the success of EOR process. The developed composition with carbon-containing natural mineral fiber (graphite) and an aluminum silicate additive (metakaolin) because of its durability at high temperature thermal cycling (<4500C) and compatibality with of Portland cement is an ideal composition for application in thermal recovery wells. The formulated thermally stable cement slurry with graphite and metakaolin has no significant effect on compressive strength and liquid permeability at high temperature thermal cycling (<4500C), thereby making it suitable for placement against combustion zone.
The field evaluation of this cement system in ISC wells of Balol & Santhal fields of ONGC in Mehsana asset is under-way. The developed novel cement system will solve the problem of charging of the subsurface shallow layers because of cement sheath failured during the in-situ combustion process.