Readers will find several game changers in this year's edition ofOffshore's annual Rotary Steerable Systems Survey. Rotary steerable systems (RSS) provide the best answer to geologic steering, or geosteering. Operators seeking formation "sweet spots" need to be guided by real-time geologic information - the kind provided by today's sophisticated logging-while-drilling (LWD) strings. Integrating accurate steering with precise formation measurements enables drillers to hit challenging reservoir targets with high quality wellbores and maximum drilling efficiency. Geometric steering, of the sort provided by extrapolation of geologic data obtained from vertical pilot holes and drilled using mud motors with bent subs, may be less expensive, but as the saying goes, "You get what you pay for."
Tight curves and high rates
Recent factors in well construction have tilted the scales in favor of RSS techniques. The ability to deliver high dogleg severity enables drillers to land their wellbores in target formations quicker and more precisely. Plus, the ability to steer long laterals into the most productive formations far offsets the cost of the technology.
Two of the systems catalogued in the annual survey address these factors. The Baker Hughes AutoTrak Curve system has drilled 3 million ft (914,400 m) of hole over the past 22 months. According to the company, the system allows drillers to land the well sooner, improve production by increasing exposure to the reservoir sweet spot, and ensure accurate well placement. High buildup rates of up to 15°/100 ft characterize this latest addition to the Baker Hughes arsenal.
The Schlumberger PowerDrive Archer RSS is designed to deliver high build rates from any inclination. Recently offshore Thailand, the system was used to steer accurately through soft formations where sediment washouts from mud flow can reduce steering capabilities. Using an integrated bottomhole assembly (BHA), the company drilled out of a milled casing window and steered an 8 ½-in. hole section in a single run at a penetration rate of 186 fph, landing the borehole within 6 ft (2 m) of the reservoir top as planned. The event marked a 66% penetration rate improvement over offset directionally drilled wells that used positive displacement motors.
An integrated drilling solution was designed that incorporated the EcoScope multifunction LWD system, a PowerDrive Archer high build rate RSS, and an application-specific PDC bit from Smith Bits, a Schlumberger company. Bit compatibility with the designed BHA was validated using the IDEAS integrated drill bit design software. Analysis showed how the bit, BHA, drillstring, well profile, drilling parameters, and geology would affect steerability, stability, durability, and penetration rate.
According to the company, the PowerDrive Archer RSS provides extra assurance that well profiles can be drilled as planned. Its increased dogleg capability gives better trajectory control in unconsolidated formations and punches through hard stringers. Finally, the ability to make directional open-hole side tracks reduces time on multilateral wells, and deep kickoff points enable reduction of inclination in unstable formations and reduce footage to reach the reservoir.
Getting off to a good start
To reach a tough target, one must ensure precision from the outset. That is why Halliburton's Sperry Drilling uses its Geo-Pilot XL RSS system to kick off large diameter vertical holes. Globally, the company has made an estimated 75 runs for 24-in. and 26-in. Geo-Pilot systems. Using a closed-loop feedback system, drillers are able to maintain a precisely vertical cruise mode to hold inclination within 0.2° or less using their ABI at-bit inclination sensor. The point-the-bit system is ideal for the soft sediments typically encountered in surface holes because it does not use pads to push against the borehole walls to make steering corrections. According to the company, the system delivers unprecedented penetration rates and up to 20% reduction in non-productive time.
In the deepwater Gulf of Mexico, the Geo-Pilot XL 9600 series RSS has been revised to accommodate 26-in. hole sections. One particular feature is a 7 5⁄8-in. box-down connection that allows direct make-up of 26-in. bits without the need for crossover subs. Sperry will use the system to drill 24 wells of which 21 are vertical. Two wells have already been drilled integrating the Geo-Pilot RSS with LWD services. Four runs comprising 114 circulating hours, 38 drilling hours, and 3,168 ft (966 m) have been tallied using the 26-in. BHA, meeting all requirements as batch drilling continues. Requirements are tight: wells must stay within a 10-ft (3-m) diameter circle to avoid adjacent wellbores, steering must be precisely within 1° of hole angle in soft sediment formations, and dogleg severity cannot exceed 1°/100 ft.
Weatherford features its Revolution RSS point-the-bit system. The system made its debut in a slim 4.75-in. size with the idea that upscaling is more efficient than downsizing. Recently, emphasis has been placed on developing the ability to drill wells all in a single run. To do this the Revolution RSS has the capability of drilling with a high degree of verticality, then drilling the build section with up to 10°/100 ft of dogleg and a smooth catenary curve. The system can then geosteer the lateral. These attributes produce high quality wellbores with low degrees of tortuosity. Three automatic drilling modes are available: vertical hold, tangent hold, and 3D autopilot.
The new system uses a long gauge bit for greater directional stability, but minimizes side cutting for maximum rate of penetration. The entire BHA rotates to minimize drag forces. Inclination and azimuth sensors are located close to the bit for timely directional feedback, and real-time vibration sensors warn drillers about potentially destructive vibration: axial, lateral, and torsional.
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