Advanced FEA Modeling Produces First Directional Tandem Reamer BHA: Eliminates Trip on Deepwater Exploration Well
Authors: Jardinez Agustin , Guzman Gumaro , Karrer Cesar , Murillo Ricardo , Verano Fernando , Araujo Juan C. , Lopez Juan Ramon 
Published: June 2014

The deepwater region east of the Mexican state Tamaulipas remains virtually unexplored despite its close proximity to prolific oil production in the USA portion of the Gulf of Mexico. To locate new reserves, PEMEX launched an initiative to outline a deepwater exploratory strategy, assess risk and classify hydrocarbon type by area. A comprehensive geological modeling study was funded to analyze Upper Jurassic and Tertiary strata with 2D/3D seismic, well logs and to map naturally occurring gas seeps and oil shows. The project enabled geologists to accurately identify several key play elements including reservoir presence/quality in addition to hydrocarbon source rocks, migration patterns and trapping mechanisms. The study characterized the area's sedimentary environments and complex structural features including growth faults and downthrown rollover folds that created multiple anticlinal features in addition to typical gulf coast salt/shale diapirs. The study concluded the offshore basin has high potential for hydrocarbon accumulations in a variety of trap styles.

To test the hypothesis, the Caxa-1 exploratory well (150km offshore) would kickoff from 3.67° and build to 6° inclination, then drill tangent for 400m. The wellbore would penetrate shale overburden to evaluate Miocene sands at 3400-4000m before reaching TD (4474m). The shale/sand section between 2900-3400m has low UCS, but engineers wanted to drillout the 18-in casing shoe without tripping for BHA change-out and still have adequate clearance to run the subsequent 16-in string without NPT. This technique would eliminate the requirement for extra 12¼-in pilot hole significantly reducing rig-days. The challenge was to build an industry-first tandem reamer directional BHA. The objective would be to complete the section in one run, deliver all directional requirements at fast ROP with minimal vibrations to allow the use of advanced MLWD.

The provider recommended a 12¼ x16½ x20-in tandem reamer BHA including an RSS driven 12¼-in PDC bit, a 12¼x16½ fixed-blade hole opener followed by an expandable reamer. The BHA would prevent ID damage to the 18-in casing and allow the operator to set 16-in casing in the next run while 20-in hydraulic opener would create adequate clearance for cementing. Real-time MLWD would be used for formation evaluation and accurate well placement. An engineering analysis was performed to balance the cutting structures, minimize vibration potential and set optimum operating parameters. Based on the simulations a 716-type PDC was selected.

The BHA drilled out the 18-in casing shoe and a 382m of section in one run at a fast ROP of 18.6 m/hr. No vibrations were recorded resulting in high-quality MLWD data. The 18-in casing was undamaged and the 16-in string was set on the first attempt. The BHA was pulled at section TD in excellent dull condition with no wear on the three tool's cutting structures. The technique was used on Trion-1 exploratory well with a similar BHA (12¼"x17½"x22"), Sumpremus-1 (12¼"x14½"x17½") and Maximino-1 (12¼"x16½"x20") with comparable results.