Obtaining good-quality sidewall cores in unconsolidated formations has been always a challenge due to the nature of the rock. For an operator offshore Mexico, core recovery in highly unconsolidated rock had a low 25% success rate, with most of the usable cores recovered in shaly zones. In-depth analysis of sidewall coring showed that debris removal and lack of core protection were the main reasons for unrecovered cores.
To improve core recovery, SLB used a tailored approach including the SureRock enhanced sidewall coring solution, the AutoCore™ automated sidewall coring system for adaptive cutting control, and core detection capabilities that enabled dynamic adjustment of the coring operation as well as confirmation of core recovery.
The first descent showed good recovery in rocks averaging a few hundred psi UCS. Advanced technologies built into the SureRock solution enabled recovery of extremely low UCS rock (<10 psi), preserving the core in good condition.
The well was drilled ahead using lost circulation material (LCM) additives to control mud loss and the SureRock solution using the AutoCore system recovered 100% of attempted sidewall cores in rocks with an average 600-psi UCS, including a fully recovered core of only ~350-psi UCS.
In this lower section, coring time was reduced to an average of 11 minutes per core while maintaining excellent core integrity and full core length (2.5 in). Overall, the project completed three runs with a combined recovery rate of 81% (39 of 48).
Ultimately, the solution even recovered intact cores that could be crushed between fingers like “beach sand.” The SureRock solution—which works in abrasive, unconsolidated, and highly overbalanced conditions—is now available to the global E&P market. Digital and hardware enhancements, along with detailed prejob modeling and on-the-job insights, enable the SureRock solution to capture cores in any oilfield environment.
