Maintaining Well Integrity in Underground Gas Storage Wells in China Using a Novel Cementing Technology
Underground gas storage (UGS) wells have become the national strategy
for natural gas storage and supply throughout China. PetroChina is building UGS
facilities throughout the country, with planned construction extending from
2011 to 2015. The Chongqing gas storage well project in Central China is one of
the constructed facilities. Because the life expectancy of gas storage wells is
at least 50 years, long-term maintenance of well integrity is one of the major
challenges faced during the construction and operations phases of UGS wells.
The wells must bear the injection pressures, temperature changes, and frequent
cycling of injection during production. With conventional cement, the pressure
and temperature change during the injection and production phases can result in
cement traction, compression, or microannulus failure. This leads to gas
migration through the damaged cement sheath, which means the well will fail its
mission as a UGS well.
To maintain well integrity, a novel engineered flexible and expanding
cement system has been introduced for UGS cementing in the Chongqing project,
whereas past service companies have failed to deliver the fit-for-purpose
solution. The optimized mechanical properties of this novel cement allow the
cement to remain intact under extreme pressure and temperature changes.
To prove the ability of the selected flexible and expanding cement to
withstand the pressure change, logging was conducted at various times during
the construction and after the casing pressure test cycle. The logs show
Since its implementation, the flexible and expanding cementing system
has become the standard solution for China’s UGS wells, in which
long-term well integrity and sustained casing pressure are required. This paper
discusses the challenges for cementing UGS wells, which case histories describe
the successful implementation of the FEC solutions.