The Eagle Ford Shale was a major contributor to the shale boom that changed the economics of the E&P industry during the past decade. Drilling activity is picking up again in the shale play after the recent downturn, but operators face ongoing well construction challenges that threaten to lower drilling efficiencies, increase nonproductive time and raise costs. Representing one of the most geologically complex unconventional plays in North America, the Eagle Ford runs the spectrum from oil in the northwest to condensate and NGL in the central area and dry gas in the southeast.

Wells in the region are increasingly drilled to a total depth (TD) of 6 km (3.72 miles) or greater, with laterals extending more than 3 km (1.86 miles) from vertical. Kicking off from the vertical to the lateral often requires drilling out highly curved sections with dogleg severities of 8 degrees per 30 m (100 ft) or more. The lateral section is then typically drilled through dense limestone and sandstone formations with ambient temperatures exceeding 155 C (310 F).

These depths and temperatures make it difficult for operators to find the formation’s so-called sweet spot— the section of the reservoir with the highest production potential—and then drill out to TD without veering off course. Conventional directional drilling technologies such as mud motors equipped with bent subs attempt to stay in the target zone by sliding: rotating the bit downhole while halting rotation of the drillstring. This technique not only reduces the ROP and drilling efficiency but also fails to deliver the high precision required for drilling complex, tortuous well paths.

Improved directional control

The industry’s need for improved drilling efficiency in long-lateral high-temperature wells prompted the development of Weatherford’s comprehensive directional drilling and MWD program. One component is the replacement of mud motors with a rotary steerable system (RSS) for directional control. The RSS includes several stabilizers placed around the tool that effectively “steer” the bit for precise drilling of high-angle curves, deep kickoffs, extended laterals, parallel vertical sections and sidetracks.

The RSS focuses the cutting force to the face of the polycrystalline diamond compact bit, improving ROP while ensuring a smoother wellbore. The system uses high-viscosity oils and high temperature-rated seals to maintain hydraulic integrity while reliably drilling vertical, curved and lateral sections at temperatures exceeding 171 C (340 F).

The bottomhole assembly (BHA) includes an MWD system designed for hostile environments that monitors downhole vibrations such as stick/slip, whirl and lateralaxial torsional dynamics. It includes a bore and annular pressure sensor to measure downhole pressures and temperatures during drilling, wiping or tripping out of hole. This sensor provides an early warning of wellbore instability problems in drilling environments in which a narrow window exists between the pore pressure and formation fracture pressure.

Near-bit inclination and high-temperature azimuthal gamma ray sensors installed in the BHA obtain realtime measurements while drilling, and a bi-directional communication system transmits the data to the surface via mud pulse or electromagnetic telemetry. If the azimuthal data indicate the wellbore is deviating out of the reservoir’s sweet spot, the operator can send control signals downhole to the RSS in a matter of seconds. The RSS then makes steering adjustments that get the drillbit back into the target zone.

Taken together, these tools can effectively drill out tortuous extended-reach laterals to TD with greater efficiency and accuracy compared to conventional directional drilling tools. A mud motor might be able to drill out a long lateral section but with more course corrections and at much lower speeds that might add days to the drilling process.

Breaking single-run records

This high-temperature directional drilling solution has set multiple lateral length drilling records for operators across the Eagle Ford. The current record holder is a well drilled to a TD of 6.9 km (4.3 miles) and with an ambient downhole temperature of 168 C (334 F).

The operator followed an established drilling methodology developed while drilling hundreds of wells in the region. But given the long lateral planned for this well and its proximity to neighboring wells, the operator needed more precise directional control. It believed that a conventional mud motor would add too much time, risk and cost to the drilling operation. The desired solution would avoid collisions with nearby wellbores, stay in the target zone and reach TD as quickly as possible while withstanding the high-temperature environment. Because the operating company had a history of successful high-temperature directional drilling projects with Weatherford, it approached the service company for assistance.

Together with the operator, Weatherford drilled the well in two runs, beginning with a standard vertical hole section drilled to the surface shoe at a depth of 1,248 m (4,094 ft). The second run, from the surface shoe to TD of 6.9 km, was conducted with the high-temperature RSS, MWD and azimuthal gamma ray tools configured into the BHA.

The system’s real-time directional control removed any uncertainty regarding the drillbit’s location in the lateral section, allowing the operator to successfully navigate the wellbore through tight spacing and remain in the target zone. The constant rotation of the drillstring allowed more efficient hole cleaning and helped achieve an ROP of 52.87 m/hr (173.47 ft/hr) for the RSS run.

The comprehensive solution successfully drilled 5.6 km (3.52 miles) from shoe to TD in a single run. Not only did this surpass the previous single-run RSS drilling record by more than 640 m (2,100 ft), it also helped the operator reach TD in eight days and meet a tight scheduling window for completing the well. The operator was pleased with the results and is continuing to work with Weatherford to efficiently drill other high-temperature directional wells in the field.

Extending efficiency gains

The application of this high-temperature directional drilling solution is certainly not limited to the Eagle Ford. Based on its recent record of success, Weatherford’s approach is attracting the attention of other operators interested in maintaining high drilling efficiency while navigating high-temperature tortuous well paths to TD.

Increased operational efficiency is always an important criterion for selecting drilling technologies in extreme-temperature extended-reach wells. But when rig rates eventually start climbing again, the need for technologies that boost ROP and drive down the number of days on a well will be even more critical. When that day comes, RSS-based directional drilling systems stand ready to deliver wells to TD with an efficiency and precision that mud motors cannot reach.

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