Coring reservoir rock has been an integral part of any oil & gas operator. With a vertically stacked multiple reservoirs in Kuwait stratigraphy cores are thus taken in various depth ranges from few hundred feet to higher than ten thousand feet. Wireline Coring technology, which has been successfully applied in various parts of the world, was found to be an alternative to cut down on rig time and maintain good quality of cores. Heavy oil shallow unconsolidated reservoir of Lower Fars was chosen to be tested with this innovative technology. This reservoir is as it is challenging for coring due to its highly unconsolidated nature with high intergranular porosity coupled with the issue of gravity settling of heavy oil which limits the individual core intervals.

The CorionExpress® technology of NOV uses a PDC core bit which has a wireline- conveyed drilling insert to convert the core bit to drilling mode in matter of minutes. This helps in taking multiple cores with intermittent drilling without the need to take the string out. 140' of core was cut in continuous runs with drilling of intermediate shale and drilling to the final depth of the well successfully without any need to take the assembly out of hole. There was substantial time saving of about 30% in rig operation for coring and drilling even in this shallow reservoir where normal tripping time is much less. Recovery percentage was satisfactory considering the technology was applied without a huge advantage of past experiences and lessons for the conventional coring for the same reservoir.

Gaps and lessons learnt indicated further scope to streamline the catcher and bit design for better recovery. It also requires rethink on operating procedures particularly in wireline rig up & rig down and core handling rig up & rig down for time saving. However, each of these factors need to be tailor made to the reservoir quality that is to be cored. This paper illustrates the thoughtful mix of technology, innovative techniques and proper coordination by aligning all concerned has helped in meeting the challenge of coring unconsolidated sand and it's processing to deliver a geologically acceptable core for laboratory studies.

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