Temperature and pressure challenges still frustrate operators and service companies working on deep and ultradeep wells.

“Equipment needs haven’t changed for onshore deep wells,” said Hermann Sporker, head of well engineering for Austria’s OMV E&P. He knows what he’s talking about. OMV drilled Europe’s first 19,686 ft, 22,967 ft and 26,248 ft (6,000 m, 7,000 m and 8,000 m) wells. It has drilled to 28,000 ft (8,540 m), and its program found a well in the Vienna Basin with an initial potential of 40 MMcf/d.

Conducting an impromptu poll of audience members at a session during the annual meeting of the International Association of Drilling Contractors, Sporker found only five people in the room who had been involved in a well drilled below 25,000 ft (7,625 m) in the past 10 years. No hands were raised when he asked if anyone in the room had a rig prepared to drill 30,000-ft (9,150-m) wells.

The industry has been doing a good job with extended reach wells to 6.8 miles (11 km), but they’re all shallower than 10,000 ft (3,050 m). “Contractors and operators will have to relearn techniques and come up with new equipment if they want to go as far vertically as they have horizontally,” Sporker said.

Deep wells present a shopping list of challenges, including drillstring torque and hydraulic requirements, well path design, catenary curves, casing setting and narrow fracture gradients. According to Sporker, the challenges are more physical than mechanical.

Sour gas can be a problem for large and deep casing strings, particularly at rock compressive strengths of more than 30,000 psi and temperatures around 500°F (260°C). The industry still needs rigs that can handle casing strings in the weights required for ultradeep wells. Sporker said he’s seen 3-million-lb designs. “The rig would need sufficient racking for casing strings, and the rig would have to be ready to handle flow rates generated by extreme pressures. At 25,000 to 30,000 ft (7,625 to 9,150 m) the well would need a choke manifold with a 20,000 to 25,000 psi capacity.”

Topside, better mechanicals will be needed to speed up the drilling process. As society asks for smaller footprints for operations, operators and contractors will have to figure out how to meet those requirements when 16,405 ft (5,000 m) of 13 3/4-in. or 22,967 ft (7,000 m) of 9 5/8-in. pipe in double layers requires 1,000 cu m of space.

Power needs call for six generators, larger rigs and mud tanks sizes dictated by high mud volumes. On the plus side, newer generators produce lower emissions, and the industry has better mud and solids control systems with fewer cuttings and liquid discharges. New rig designs even include soundproofing.

Sporker states that the real challenges are:

  • Controlling the pressure gradient;
  • Managing downhole pressures higher than 20,000 psi;
  • Managing the well control system;
  • Drilling a well with more than 6,000 psi of standpipe pressure;
  • Designing fluids that work at 500°F (260°C);
  • Managing drillstrings with the strength to support to pipe and be compatible with sour gas; and
  • Designing drill bits and understanding rock behavior under 30,000 psi of stress, when rock turns plastic.

The industry still is on uncertain ground in some mechanical areas. Measurement-while-drilling and logging-while-drilling equipment and downhole motors may not be reliable at temperatures higher than 500°F. On the seismic side, 3-D and 4-D information may not present needed resolution at 23,000 ft (7,015 m).

For these ultradeep wells, the industry will have to relearn good drilling practices such as stabilizer placement and drillstring dynamics in vertical holes. Drillstring treatment can make a big difference if a twistoff loses the well.

Sporker also said only a couple of wells per year go below 25,000 ft (7,625 m), and the industry needs five to 10 of them to learn enough to bring down costs. If learning remains scattered, costs will remain high, he said, particularly when land rig contractors are reluctant to build rigs with that capacity for only a couple of jobs a year.

As several high-pressure/high-temperature articles nearby indicate, progress in this area is not entirely stagnant. And ultradeep wells have been drilled for scientific purposes; the German KTB project and the Russian superdeep Kola SG-3 project come to mind.

But he has a good point. In order to routinely drill ultradeep wells for commercial oil and gas production, Sporker believes industry players should team up and share information about well challenges in ultradeep and superdeep wells. “They should share successes and train wrecks and create an information platform for ultradeep wells.”