Results of record-setting deep core operation in the southern region of Mexico by PEMEX Exploration and Production showed that efficient deep core recovery-is possible in a difficult formation, even at depths exceeding 22,000 ft (6700m).

The complexity of coring limestone can involve such problems as coring jamming, which lowers recovery ratios. In addition, limestone may have fractures which can complicate core recover/ by causing jamming or restricting entrance of the core into the inner barrel.

However, in this instance, a 97% core recovery rate was obtained using a conventional 4-3/4" coring assembly with aluminum inner tubes, and a 5-7/8" × 2-3/4" natural diamond core head.

Performance data, operational details, and economic analysis concerning use of this type of coring assembly is presented. The data describes the overall success of coring performance in limestone at extreme depths.

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