Coiled tubing use extends offshore productivity

New uses for present technology with new equipment to further effectiveness

The Coiled Tubing and Well Intervention Conference, sponsored by ICoTA, the Intervention and Coiled Tubing Association, was held in late March in The Woodlands Conference Center north of Houston. Speakers presented a range of operational experience, practices, and well intervention improvements using coiled tubing and other techniques.  Sessions included electric line, slickline, and wireline operations, fracturing and stimulation using coiled tubing (CT), as well as offshore and subsea well intervention. Among the highlights:

Velocity strings

In the North Sea, older fields are being brought back into production by installing coiled tubing as velocity strings to unload excessive fluid from gas wells. Speakers from Netherlands-operator NAM (Nederlandse Aardolie Maatschappij)presented SPE 163905, “Extending the operation life of mature North Sea assets by big-scale offshore installation of large-diameter chrome coiled-tubing velocity strings.”

NAM installed 2 3/8in. and 2 7/8in. 16-Chrome coiled tubing in 20 wells, using a dedicated, self-propelled jackup during a two-year, field-life extension project. The crew installed the pipe in wells on small production platforms and unmanned installations after a careful evaluation process to identify wells that would best benefit from deliquification. Gas production after the workovers increased by 1.7–5.3MMcf/d per well, returning the wells to profitable operation and extending their economic life.

Clean cutting

Welltec won ICoTA’s seventh annual Intervention Technology Award for a new tool, the Well Cutter, and was presented with the winner’s trophy, the Quaich cup, which it later displayed in its booth. The electric-line conveyed tool is a mechanical cutter that uses grit-embedded pads to cut tubulars. The pads are expanded outward at the bottom of the tool to contact the inner pipe wall, and then are rotated to sever the pipe. 

The tool’s operation was explained in technical paper SPE 163890, “Electric-line pipe-cutting operation optimizes completion removal, offshore Russia.” During the operation, the tool successfully cut a 4½-in., 12.6lb/ft tubing below 2,133m, in a 57° deviated well off the east coast of Russia. Cutting time was about 80 minutes.

Metal filings produced by the pads were easily flushed out of the wellbore, unlike shards from explosive cutting, or metal chips and curls from a milling tool. Because the cut was clean, no additional trip to collect junk or dress the top of the remaining pipe was required. The cut left a smooth, beveled interior surface to the pipe, which was easily fished, and the remaining pipe pulled.

The operator Sakhalin Energy, realized significant cost savings because no explosives were used to cut the pipe. They did not have to pay for explosives permits, follow special procedures, provide additional security or special storage, limit radio or vessel traffic, or spend extra rig time on secondary runs to dress a flared, ragged pipe end.  The tool can be used on drill pipe, liner, tubing, packers, or casing.

Vibration-enhanced drilling

Traditional mechanical water hammer systems operate at frequencies of 12-40 Hz, are generally preset for a given drilling mud circulation rate, and are not adjustable. The programmable pulse technology in the new tool allows the pulse amplitude to be varied without tripping out of the hole.

Another new tool at the event was presented by TeleDrill Inc. in SPE 163883, “Low frequency water hammer for extended-reach applications.” The CT-MWD (coiled tubing-measurement while drilling) tool sits behind the bit and uses an actuator system to create low-frequency vibrations in the drilling mud stream that serve two purposes. First, the vibration excites the coiled tubing (CT) to keep it moving through tight sections or when lying against the bottom of the hole while drilling lateral sections. Second, the induced fluid vibrations can be used to transmit data uphole from other sensors in the bottom hole assembly.

The tool modulates circulation pressure in the 1.5-2Hz frequency range to vary load on the bit, creating axial oscillation in the tubing. This “ballooning effect” reduces friction along the pipe, prevents helical buckling, improves weight transfer for milling and drilling operations, and increases CT reach. The tool is continues under development and additional field tests are scheduled later this year. OE

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