Successful cementation of low fracture gradient reservoir sections poses its own challenges for the operators. Such cement systems shall be competent enough to endure the stresses being imposed throughout the life cycle of the well ( cycles of pressure and temperature changes imposed by perforations, well testing, work-over operations and etc.) and at the same the existence of relatively low fracture gradients formations will limit the upper range density of such systems.
Blended light weight cement systems by adopting a new approach to designing cement slurries effectively decouple the physical properties of set cement from the slurry properties and density, resulting in high performance lightweight cement slurries. Conventional blends have some components with limited pressure rating that will collapse trader high pressure and therefore the slurry properties can change dramatically to the point where the cementing job objectives can be jeopardized. The before mentioned challenge becomes more evident when the case is related to the cementation of a deep and low fracture gradient reservoir section.
Rajian oil field in north of Pakistan have been put into regular production since 1994 with reservoir section total depths of 3850 m ( +/ -). Recent development wells required the operator to use light weight cement where conventional light weight blended solution could not be utilized due to the excessive down-hole pressures those system would be subjected to during the cementation operations.
This paper will briefly review the existing methods to achieve light weight cement slurry and will focus on the high-pressure light-weight blended slurry system through a case study in Rajian field.