Drilling Report

New offset stabilizer allows rotary steerable system full 3D rotary control

The new technology has seen six jobs. Here are some experiences from the Middle East.

Malcolm Greener, Andergauge

The drilling industry might remember when Andergauge entered the market with a 2D control stabilizer, which is still widely recognized. It is a natural evolution from that proven technology to the recent commercial launch of the DART – a purely mechanical, 4-3/4-in. control stabilizer tool that provides full 3D rotary control in 6-in. to 6-3/4-in. hole.

The company firmly believes that a two-tier market exists for rotary steerable technology, and sees its niche in smaller hole sizes in the lower-cost land markets of the Middle East and US. With this focus, the Middle East has been the site for the initial launch, and the company’s tool fleet, spares inventory and engineering support has been centered at its operations facility in Dubai. Since its launch in Dubai, the new technology has seen six jobs and drilled in excess of 8,000 ft over 200 hours.

TOOL DESCRIPTION

The new stabilizer drills a curved path by using an offset stabilizer and three-point geometry to achieve the desired well trajectory. Orientation of the control stabilizer is maintained by an eccentric mass, which hangs to the low side of the hole. Changes in direction are achieved by a quick downhole adjustment of the orientation between the mass and the offset stabilizer.

Research and development on the tool started in 1996, leading to prototype testing in early 2001, field trials through 2002 and 2003, and the commercial launch in mid-2004. The development was helped greatly by the creation of a model that was used to drill over 160 ft of 1-3/8-in. hole, in concrete, to prove the concept and fine-tune the stabilizer offset. Development was further accelerated with the purchase of a river crossing rig, which proved invaluable in allowing instant feedback from horizontal test drilling. Before launch, the new stabilizer had successfully drilled over 2,500 ft and clocked up 260 circulating hours.

CASE HISTORY, DUBAI

The first operator to commercially embrace this technology was the Dubai Petroleum Co., Fig. 1. DPC had successfully drilled a previous horizontal well to a total depth of 22,117 ft using conventional steerable motor, sroller cone bits and AG-itators (an Andergauge product that creates an oscillation in the BHA, improving weight transfer to the bit), all aided by the addition of mud lubricants and glass beads. An ambitious plan for a lateral sidetrack of another existing well, to a record depth of 23,300 ft, indicated different technology was required.

Fig. 1. Crews ready to go in the hole with the new control stabilizer on a Dubai Petroleum Co. well.

Halliburton’s Sperry Sun was to sidetrack the 6-1/8-in. hole, off a whipstock set in the 7-in. casing. It was realized that a PDC bit would be required to facilitate the economic drilling of the well and this would preclude the use of steerable motors. DPC, therefore, explored the use of a rotary steerable system, and opted to run the DART to maintain the 6-1/8-in. horizontal section and geosteer well trajectory in rotary mode to TD, as dictated by geology.

The new stabilizer and PDC bit were run in the well at 19,116 ft. Previous runs to this depth had used an AG-itator and a Sperry Sun SlickBore motor with a roller cone bit, so reaming the PDC to bottom was not necessary. The stabilizer was used from 19,116 ft under full rotary directional control over the entire 691-ft interval, until shale was encountered at 19,807 ft, necessitating the assembly to be replaced with a steerable motor. The stabilizer was cycled 11 times, with each tool face alteration taking about three minutes, and averaged an ROP of 39.26 ft/hr over the 691 ft drilled.

A rock bit, with a slick steerable motor and an AG-itator, was used to perform an openhole sidetrack, and subsequently drilled 1,925 ft at an average ROP of 27 ft/hr. The assembly experienced difficulty sliding, even with the addition of lubricants, and was pulled at 20,975 ft.

A second DART assembly followed, and required light reaming to bottom over the entire interval drilled with the slick motor. The new offset stabilizer continued to accurately geosteer as per the target requirements, passing the previous record of 22,117 ft and intersecting the target at 23,300 ft. The well was extended 678 ft farther, beyond the primary target before geology called final TD at 23,978 ft, Fig. 2. The stabilizer was cycled 40 times over the interval, with each tool face alteration taking about four minutes. An average ROP of 58 ft/hr over the 3,003-ft run was recorded. It was also noticed that reductions in torque and pump pressure demonstrated that the well could easily have been extended much further.

Fig. 2. DPC well plan, showing footage drilled with the new offset stabilizer in red.

The operator realized savings by running the new tool. Savings and benefits noted were:

• Improved ROP
• Elimination of a bit trip
• Marked reduction in torque and pump pressure
• Ability to geosteer along the extended section.

The above benefits from the new tool have resulted in firm plans for DPC to use it in future, similar applications.

CASE HISTORY, OMAN

Following a previous successful field trial, an operator in Oman selected the new stabilizer as the preferred directional control method to geosteer a 2,300-ft lateral section. In addition to ROP gains, the operator was hoping to improved hole quality. During the field trial, the stabilizer had been followed by a steerable motor, prior to the hole being calipered at TD. The caliper log clearly showed the smooth, 6-1/8-in. wellbore produced with the new stabilizer, Fig. 3.

Fig. 3. Caliper log in lateral section.

SECOND WELL

The main objectives for the second well were to complete the section in one trip, maintain the well path within the required TVD and directional tolerance, and achieve an ROP increase over conventional motor-drilled offsets.

The horizontal section was successfully geosteered from 4,900 to 7,300 ft (Fig. 4), with a 25% increase in ROP. The trajectory was maintained within a tight target corridor by cycling the tool face 32 times over the course of the section. The cycling of the new stabilizer merely involves coming off bottom, shutting the pumps off, and rotation; each tool face change took less than three minutes. The tool’s performance and predictable 3°/100 ft steering resulted in the operator wanting the tool on contract for future lateral applications.

Fig. 4. Actual versus planned well path.

FUTURE PLANS

The company’s short-term plans are to continue to build a 4-3/4-in. DART tool fleet, and to support Middle East operations to the point of self-sufficiency, before entering the US land market.

The new stabilizer requires a hole inclination in excess of 45° to maintain orientation of the mass, so hole sizes in excess of 8-1/2-in. are of limited potential. The company has prototype drawings for a 6-3/4-in. tool, but further R&D is being directed at smaller tools. The 1-3/8-in. working model, which proved the DART concept, indicates that the tool can be slimmed down substantially for the emerging in-field drilling re-entry market.

In addition, it is anticipated that the continued development of the company’s AG-itator and Hydraulic Anderreamer will realize component life improvements in excess of 100%, similar to earlier products, and that this same process will benefit the new stabilizer over the next five years. The company believes that the purely mechanical DART will become one of the lowest-cost rotary steerable systems available. 

THE AUTHOR
	Malcolm Greener joined Andergauge in 1994, after following a progressive career, through surveying and directional drilling, into the operational management of numerous international locations with Eastman Whipstock /Baker Hughes INTEQ. At Andergauge, he has progressed from European operations manager to managing director, holding the latter position for the past nine years during which he has directed the dynamic international growth of the company. He holds a BSc in engineering and management, from Brunel University, and is a member of SPE.