Technology Focus: Casing and Cementing (May 2009)

Technology Focus

The current trend in well construction technology is focused on reducing the risk associated with capital-intensive wells in deeper and/or increasingly hostile environments. With a water depth between 4,000 and 11,000 ft, total depth approaching 30,000 ft, and a total cost per well of USD 200 million to 300 million, the deepwater projects being developed around the world are a prime example. One significant design error or oversight can lead to well failure and have serious effect on a company’s bottom line. With mudline temperatures as low as 34°F and production temperatures as high as 250°F, annular temperatures may increase by more than 100°F during production cycles. As the annular fluid heats up, it expands. If that fluid is in a confined section of casing/casing annulus, the annular pressure can exceed 10,000 psi. This phenomenon has led to rupture or collapse of casing strings and loss of some wells. One approach to mitigating this phenomenon is to use vacuum-insulated tubing to limit heat transfer to the trapped fluid. Another is the novel use of a new annular fluid that shrinks rather than expands as the annular temperature increases.

A greater proportion of our future energy will come from more-hostile environments as we increase the pursuit in deepwater, high-pressure/high-temperature, geothermal projects while using CO₂-storage wells to reduce CO₂ emissions. These wells may contain high levels of H₂S, CO₂, and/or chlorides and have temperatures in excess of 350°F. Proper selection of tubulars, anatomic seals, and cement will be critical to reducing total well cost and environment and commercial risk. 

I asked one of Chevron’s cementing experts (Robert Carpenter) for help with current cementing technology. With the growing concern about “carbon emissions” and “carbon capture,” CO₂ injection for geological storage is our next big area of activity. The success of this industry segment is predicated on very-long-term isolation of injected CO₂. We are in the investigational stage of this rapidly growing industry segment, and the primary issue is ensuring the long-term integrity. 

There is extensive debate and conflicting laboratory and field investigations into the suitability of Portland cement for a CO₂-rich environment. Recent investigations indicate identifying and preventing existing cement defects as the primary concern, and the CO₂ attack on Portland cement as less of an issue.

Casing and Cementing additional reading available at the SPE eLibrary: www.spe.org

SPE 115638 • “Advanced Cement Systems Used to Improve Geothermal-Well Reliability in Java” by K. Ravi, Halliburton, et al.

SPE 119504 • “The Effect of Carbonic Acid on Well Cements as Identified Through Lab and Field Studies” by A. Duguid, SPE, Schlumberger.