Technical Paper: Solving Deepwater GoM Pore Pressure Puzzle: Multiple Activation Reamer Eliminates Trip Prior to Running Coring Bottomhole Assembly

Society: SPE
Paper Number: 167916
Presentation Date: 2014
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The nature of pore pressure profile on deepwater Gulf of Mexico wells dictates the need for hole enlargement while drilling (HEWD) on several intervals. HEWD is a well-established practice in deepwater GoM and allows casing programs with smaller ID clearance between consecutive casing strings. 

Although the reservoir section is typically drilled as a single diameter, HEWD is required for many of the larger upper hole sections. However, in some cases drilling conditions require the operator to deviate the casing program from plan. On a recent deepwater Gulf of Mexico Lower Tertiary well, pore pressure anomalies, high mud weight and associated equivalent circulating density (ECD) required the operator to raise Formation Integrity Test (FIT) to the maximum limit while drilling the 14 1/2 by 16 1/2-in section. To solve the problem required premature setting of a 14-in casing string. 

The subsequent 12 1/4-in section was initially planned as a single diameter drilling interval. However, to account for pore pressure variations experienced on the previous section and to avoid narrowing of the producing casing size the plan was modified to incorporate a contingency liner. The 12 1/4-in section would have to be enlarged to 13 1/2-in case a contingency 11 7/8-in liner was needed. Adding to operational complexity, the original drilling program included a plan to core the 12 1/4-in section. To stabilize the coring BHA would necessitate a minimum of 250 ft of 12 1/4-in rat-hole. To achieve all 12 1/4-in objectives, would require an extra unplanned trip. 

To solve application intricacies, the operator elected to use a new-type ream-on-demand (RoD) system in the 12 1/4-in section and eliminate multiple trips to change out BHAs. RoD technology is equipped with an innovative hydraulic mechanism that can be opened and closed multiple times as required while drilling. 

After risk assessment and pre-job planning, the 12 1/4-in section was successfully undreamed to 13 1/2-in diameter with the RoD tool. The pressure regime was carefully monitored and it was determined the 11 7/8-in contingency liner was not required. The reamer was then closed at the top of the coring section and a 12 1/4-in borehole was drilled an additional 250 ft offering the required stabilization for the subsequent coring run. Utilization of the RoD technology eliminated a round trip prior to using the coring BHA significantly increasing operational efficiency while enhancing project economics.

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