Technical Paper: Ream-On-Demand System Eliminates Dedicated Trip to Enlarge Rathole in Deepwater Gulf of Mexico Operation

Society: SPE
Paper Number: 166127
Presentation Date: 2013
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Hole enlargement while drilling (HEWD) is a frequent and well established practice in deepwater Gulf of Mexico operations. The most common BHA design positions a concentric underreamer above the complex MWD/LWD string to enable activation, increase stability and to ensure the enlarged borehole does not degrade LWD image quality. However, this conventional BHA configuration for HEWD results in a rathole of approximately 160 ft at TD. To open the rathole to an adequate size to accommodate the subsequent liner string, the operator is forced to trip the drilling BHA back to surface and perform a dedicated hole-opening run. This procedure is costly and can add a day or more to the well construction timeline. In a recent offshore well, the operator wanted to eliminate the trip to enlarge the rathole and land the liner shoe closer to the section TD. 

To accomplish the objective, a dual reaming BHA system was developed with a conventional 12 1/4 -in x 14 1/2 -in expandable underreamer deployed above the MWD/LWD and a new ream-on-demand (RoD) system positioned between the RSS and MWD. The RoD tool is equipped with an innovative hydraulic system that can perform multiple activations/deactivations of the cutting blocks. Because the RoD system does not require a ball drop to engage, BHA design flexibility is greatly enhanced. 

Optimal tool configuration was determined by modeling the BHA with an FEA-based engineering system. The directional response of the RSS was also modeled to ensure the placement of the RoD system did not interfere with RSS directional capabilities. The RoD cutter blocks were configured to be passive when retracted to enable the underreamer to act as a control stabilizer providing a pivot-point for the push-the-bit RSS. At section TD, the plan was to pull the RoD tool above the rathole, activate the RoD cutter blocks and enlarge the 12 1/4 -in hole to 14 1/2 -in as required. 

The new tandem underreamer BHA was deployed on the deepwater project and drilled 1221 ft of section in 14.45 hrs at an average ROP of 110 feet per hour, while opening the 12 1/4 -in pilot hole to 14 1/2 -in with the conventional underreamer. After reaching TD, the RoD system enlarged the 153 ft rathole from 12 1/4 -in to 14 1/2 -in in only 3.5 hrs. The utilization of the dual hole opening system, in conjunction with an MWD/RSS eliminated the need to perform a dedicated rathole run to achieve the desired liner shoe depth. This paper covers the application the RoD system, tool design and pre-job risk assessment which saved the operator 16 hrs of rig time and reduced project costs by approximately $625,000 USD.

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