May 1999 Vol. 220 No. 5  Drilling

Robert E. Snyder,  Editor

Some more new technologies

Schlumberger says it is about to release a completely new approach to coiled tubing called CT Express. Now being tested in Alberta’s oil fields, the service reportedly rolls up to the wellsite on two trucks instead of four, rigs up in less than one-half hour instead of three, and can be operated more safely, with fewer people and at lower cost than traditional CT units. Initial units have been built for the shallow to intermediate land market (20,000-ft depth), and systems suited to offshore and deep land segments are "not far behind."

Some parts of this new unit may look familiar. The company says it hasn’t lost the curved injector head (although its design is new), the CT reel, or the tubing itself, but little else remains the same. One of the key players in the development, W. Van Adrichem, says the product team, "Purposefully analyzed the traditional CT process, which is essentially 1960s technology, to determine which areas were most hazardous, inefficient and costly. This data then drove the new design."

The new service includes a single CT vehicle and a single pumper truck, both featuring improved road handling and stability — there is no need for a crane truck. The vehicle includes the CT reel, tubing, a self-erecting mast, a prethreaded injector head, and an ergonomically advanced control cab. Reportedly, the single largest CT safety hazard — rigging up and handling the injector — has been eliminated by incorporating the new mast and prethreaded injector head.

The developer says a single pumper truck takes care of N2 and liquids storage and pumping functions. Further, all hydraulic connections, and potential human error associated with securing all of these connections, have been eliminated. More reliable process control technology (electronics and computers) has taken their place.

One person operates the CT process from the control cab, using two computer screens that bear icons illustrating the functionality of all subsystems involved. One or two other people are needed on the ground to aid rig-up and troubleshoot. Van Adrichem says there was some resistance in the field to the move away from the familiar hydraulics and CT process, "but it hasn’t taken long for our crews and the operating companies to get used to the electronics-based system and appreciate its advantages."

Testing in Canada will be completed in May, at which time, a second unit will be undergoing trials along the U.S. Gulf Coast. Commercialization should take place during the third quarter.

New mud helps shallow water flow problem. In March, Vastar reported a significant oil discovery on its Mirage prospect in Mississippi Canyon Block 941, in 4,000-ft water in the U.S. Gulf, 80 miles SE of Venice, Louisiana. Drilled with Diamond Offshore’s Ocean Victory semi, the well encountered nearly 300 ft of oil pay. The company said the Mars basin, in which Mirage is located, is a "notoriously challenging area to drill," and another operator reportedly had problems there due to shallow water flows.

Baroid has announced that it had something to do with drilling Mirage that helped solve the shallow water flow problem. The company’s new process, which had not been attempted before, involved a new, solids-free, drill-in fluid composition that created the needed formation control weight without high volumes of solids.

A shallow gas zone was encountered and a unique procedure was developed to drill this portion of the well riserless, using large volumes of a specially formulated Dril-N fluid. The logistics involved to provide the large volume needed to overcome these zones made the steady supply of fluid by barge impractical. Since returns from this riserless program were released at the seafloor, the rig had to carry all the fluids needed to complete the program.

For this project, the fluids were stored in the legs of the semi rather than being brought out on a barge. Roughly 26,000 bbl of the dense fluid was stored in the ballast tanks of the vessel, since the fluid contains no solids to clog pumps or make it difficult to remove from the legs.

The drill-in fluid was mixed with 5 lb/bbl of calcium carbonate while being pumped from the legs at 20 bpm. Shallow gas containment was made possible by N-VIS HB suspension agent additive, which suspended the calcium carbonate in the fluid. This allowed the fluid to achieve a high enough weight to contain the gas and allow the first casing string to be set. Conventional drilling fluid and a riser system was used after the string was cemented.

Conventional muds would have required addition of large amounts of clays and other solids to reach enough weight to hold back the gas. It would not have been possible to add such a high volume of solids at the required pumping rates, the mud company says. The additive uses a heavier brine as a base fluid so it reportedly does not require such a high volume of solids.

Directional drilling success. Baker Hughes Inteq reports that its AutoTrak Rotary Closed Loop Drilling System (RCLS) achieved a significant milestone in February, when the technology accumulated 300,000 ft of hole drilled. The system achieved this mark on the extended-reach Well 31/5 J-11AH in Norsk Hydro’s Troll field, where it precisely geosteered an 8,586-ft horizontal section in only 8.9 days, compared to 14.3 days for conventionally drilled offsets.

Triple Combo formation evaluation LWD sensors, a custom-engineered bit, and a downhole thruster contributed to this performance, which saved the operator an estimated $1 million in rig time. In the past two years, the system has recorded a number of other notable runs in the North Sea. RCLS, developed with ENI’s Agip Division, is the first commercial rotary steerable system. After field trials in Italy and Scotland, it was introduced to the market in 1997.

The system controls the well’s course during continuous drillstring rotation, combining downhole steering, automated control, LWD and two-way communication. And it reportedly overcomes limitations of steerable motor systems. With improved rates of penetration, ability to place horizontal wells accurately within geologic targets, and creation of "smoother" bores, potential benefits include the ability to develop fields with fewer wells and fewer platforms.

Copyright © 1999 World Oil
Copyright © 1999 Gulf Publishing Company