2nd Well Bore Integrity Workshop Princeton, NJ, 28-29 March 2006

Publication Overview

There were a number of reports that indicated that well integrity may be a current issue within the oil and gas industry. A detailed study on production wells in the Gulf of Mexico indicated that up to 60% of wells had casing pressure problems, which could indicate that the integrity of the wells had been compromised. Experience from the Permian basin in the USA indicated that when fields were changed over to CO₂ flood that significant remedial work was needed to pull and re cement wells that had not seen exposure to CO₂. It was considered that many of the problems in both the Gulf of Mexico and the Permian basin resulted from poor well completions at the outset. This may be due to cases where the casings were not cleaned properly prior to CO₂ injection and the presence of residual mud in the wells led to poor seals between the cement and the formation and the cement and the casing liner (steel). Similar issues could arise due to too rapid curing of the cement, or poor cement squeezing. Where poor seals occur ingress of saline water from overlying aquifers can results in chlorine induced corrosion of the steel casing liner. The API has recognised this as a major problem and in response it is developing a new set of standards for well completions. A further set of standards for wells in CO₂ floods us also being developed but this is at an early stage.

Publication Summary

1. There is clearly a problem with well bore integrity in existing oil and gas production wells, worldwide.  The main cause of this problem appears to be poor cementing practices.  This problem has been recognized by the industry and new standards are being introduced to reduce this problem in the future.  However, this leaves a legacy of old wells in oil and gas fields which may need extensive reworking be fore they can be considered suitable for use in CCS operations and to ensure their long term integrity.
2. It is established that cement can be degraded by CO₂, however the degree of degradation observed in laboratory tests and from the limited field samples available show large differences.  Laboratory experiments infer that the cement in the wells will be degraded in a matter of days, whereas field data shows some degradation has occurred but nothing like as severe. More field based samples are required and better correlation between reservoir conditions and the laboratory experiments are needed.
3. Whilst cement is one issue, potential corrosion problems with the steel casing and elastomer failures should not be overlooked as possible causes of leakage in wells.  Improved well completion practices may help by reducing CO₂-brine access to the metal casing, by improving cement integrity within the well.  However, for the long term i.e. after abandonment it might be best to remove the tubing and fully seal with cement.
4. New CO₂ resistant cements are now coming onto the market, but we need to establish cost issues and the suitability of these cements to provide good casing and rock seals in real applications