Managing loss-of-control in deepwater drilling

A shortage of rigs to drill relief wells and lack of knowledge are two drawbacks to managing well control in deepwater.

Deepwater exploration has become a multi-billion dollar industry, not only in terms of potential returns to oil and gas companies but also in terms of the number of semisubmersibles and drillships under construction, conversion or modification to supply the industry with the necessary deepwater tools.

One major concern among oil companies and drilling contractors is how the industry would be able to handle well control events or potential hazards as it approaches the ability to drill in 10,000 ft. of water. Publicly, at least, most well control specialists are confident of their ability to control a blowout or other drilling hazards in deep water. Their main concern is whether a qualified rig will be available to drill a relief well.

Oil and gas companies usually know the geology of the area in which they are drilling, unless it is in a wildcat area. They can determine to a certain extent through seismic interpretations whether a well will encounter high-pressure formations.

Experience and information from other wells in the area also aid the drilling engineer. This is done as a matter of course through the well planning phase. Mariner Energy, for example, uses consultants to interpret seismic data and to perform a drilling hazard analysis on its wells before drilling.

If the company does not have seismic information for the particular area in which it is planning to drill, Mariner will contract for a special limited 3D shoot of the area typically to about 6,000 ft. below the seafloor. "A lot of the well control issues are at shallow depths in deep waters," said Clint Smith, vice president of operations at Mariner Energy.

Deepwater sediments also result in less pressure than other shallower areas. "Deep water has less pressure because it is a colder environment and it is fairly sandy, so the pressure leaks off," says John Desantus, an engineer with Phillips Petroleum in Houston. "A lot of operators were surprised to find low pressure in deepwater areas." Desantus also said pressure gradient can sometimes be determined from the seismic velocity when interpreting seismic data. This can be done from 2D and 3D seismic and also is a function of how well the velocities are analyzed in conjunction with reference wells.

Interpretive software

Interpretive software is available to the drilling engineer to determine pore pressure and fracture gradient in a formation. Measurement-while-drilling (MWD) and logging-while-drilling (LWD) technology aids the drilling engineer with real time data to determine whether formation pressure is rising or falling.

One company that has developed such software is Knowledge Systems in Stafford, Texas. Among the company's clients are many of the largest international oil and gas companies along with several independent operators, including Shell, Chevron, Norsk Hydro, BP, Statoil, Amerada Hess, Conoco, Santa Fe Energy Resources, Occidental and Mariner Energy.

"Our business is accelerating because of deepwater activity," said Steve Hobart, director of applications engineering with Knowledge Systems. Knowledge Systems' DrillWorks/ PREDICT software is an interactive engineering system that aids the drilling engineer in predicting pore pressures and fracture gradients.

Drilling engineers have been predicting pore pressures for many years utilizing seismic information and other well information, but the software makes the process much quicker and establishes a database of well information, allowing the engineer to make changes in the well model.

The drilling engineer begins by collecting all of the relevant data for a well to be planned and enters the data into the DrillWorks/PREDICT planning database. The engineer can quickly perform functions including placing shale base lines on lithology curves, such as the SP or Gamma Ray, and trend lines on the derivative shale data from porosity logs.

Lithology curves can be viewed simultaneously with porosity curves to interactively set a normal pressure trend line using the derived shale data. The software can also help determine casing setting points based on user-defined kick tolerance and differential sticking considerations.

Geopressure Systems, a division of Knowledge Systems, provides all of the services covering all aspects of formation pressure work involved with well planning and drilling. On a typical project, geopressure engineers work with the customer to collect data and review the drilling, geological and pore pressure plans for the well. A pore pressure prognosis is then generated for the proposed well using DrillWorks/ PREDICT with any available combination of seismic and offset well data.

Upon arrival at the wellsite, the geopressure systems engineer installs a computer system with the software, loads all of the relevant prognosis and offset well data and then connects the system to the MWD/LWD contractor using a simple RS232 connection. While drilling is underway, a foot by foot computation of pore pressures and fracture pressures is generated and continuously compared with the forecast.

"Despite the many recent advances in drilling technology, accurate geopressure analysis remains a challenge," said James W. Bridges, President and CEO of Knowledge Systems. "In these days of escalating rig rates and problematic deepwater exploration, we have demonstrated the ability to substantially reduce drilling costs for our customers."

More important than cost is the risk to human safety from inaccurate geopressure estimates that can result in fires and blowouts, the company said.

Well control services

Unfortunately, as more wells are drilled, the higher the likelihood that a blowout or other major well control event will occur. Virtually every operator has an agreement with one of the top well control specialists - including Boots & Coots International Well Control, Wild Well Control, and Neal Adams - that ranges from consulting during well planning to controlling a kick to controlling a full-fledged blowout.

Boots & Coots International Well Control, for example, recently signed a framework agreement with Shell International Exploration and Production BV to provide well control services for the group on a worldwide basis. The agreement covers contingency planning, prevention services and training drills for all of Shell's rigs and platforms worldwide in addition to environmental cleanup, well control and production restoration operations necessary in the event of a well blowout.

Wild Well Control Inc. also signed the exact agreement with Shell, according to Pat Campbell, Vice President for the company. The only difference is that Shell would call Boots & Coots first should a well control event occur, and then Wild Well Control if Boots & Coots was unavailable, according to Larry Flak, Engineering Manager with Boots & Coots.

Should a significant blowout occur in deepwater, nearly all well control companies appear confident they could handle any situation. However, Paul Saulnier, Manager of Cudd Well Control, said the industry does not have the ability or equipment to control a full-fledged blowout in deepwater. "Well control companies don't have the money for R&D," Saulnier said. "The oil companies are concerned but don't have the time for R&D."

But other well control companies say they do have the ability to control a full-fledged deep water blowout. The first thing to do is to begin drilling a relief well in order to provide a conduit from the rig to the wellhead to begin pumping operations to try and control the well.

"The only prudent thing to do is begin drilling a relief well," said Campbell (Wild Well Control). "But you also look at all other methods and options for direct intervention of the well to determine if there are other things to do to control the well."

Flak agrees: "The first thing to do as a matter of course during a sustained blowout is to begin drilling a relief well. In some conditions, you can get the rig directly over the well blowing out. But, if it's a great flow, then you can't see to stab into the well."

One of the top concerns of Boots & Coots and Wild Well Control is having a rig available to drill a relief well. Virtually every deepwater rig is under contract. The rig drilling the original well could be used, but what happens if it is damaged during the blowout or sustains damage from riser recoil when disconnecting from the well. In some cases, the rig could be in a shipyard from several days to several weeks to repair such damage before it could return to the blowout.

Once a rig is available, drilling a relief well in deepwater would not be any more difficult than drilling one in a few hundred feet of water. "There would be no problem intercepting a well in deep water," said Campbell. "It's no different than drilling in shallow water. Directional control is much better today. MWD technology makes steering the relief well to the blowout well easy."

"Drilling a relief well in deepwater is not more difficult than drilling the original well," Flak says. "With today's directional and ranging technology, we can very precisely run a logging tool that will find the steel in the original well."

Controlling the flow

Deepwater blowouts, while potentially disastrous, have certain advantages over blowouts in shallower waters, says Flak. First, hydrostatic pressure in deepwater helps control the flow. Hydrostatic pressure in shallow water could be 70-100 psi, but in water depths of 10,000 ft, hydrostatic pressures could be as high as 4,000 psi. This allows the well control specialist to reduce the volumes and pump rates of fluids necessary to kill the well.

"High pump rates are limited by high hydraulic friction rates as the fluids are pumped into the well," Flak said. "Reactive fluids could be pumped separately into the wellbore that, when combined, solidify quickly to form a plug and close off the flow." Such reactive fluids have been patented since the early 1960's, says Flak, but they have never been applied to deepwater before because there has not been an occasion to use them.

Ocean currents are another advantage. In deepwater, the ocean currents would move the column of oil and gas away from the rig as they rise to the surface. As the hydrocarbons begin their ascent in mile-deep water, for example, ocean currents could move them hundreds of yards or even miles from the rig, reducing the chance of gas accumulating under the rig. And as the oil and gas break the surface, they would dissipate in a larger area, also reducing the chance of explosion and fire.

Task force establishing deepwater well control guidelines

The offshore industry is taking a proactive stance with regard to deepwater well control with the formation last year of a task force to develop and publish guidelines specifically relating to well control issues and practices in deep water drilling operations. The Deep Water Well Control Task Force is headed by the International Association of Drilling Contractors in conjunction with the Offshore Operators Association.

"First and foremost, safety has to be our primary responsibility," said Moe Plaisance with Diamond Offshore, who is Chairman of the task force steering committee. "Increased operational efficiency goes hand in hand with safety," he said.

The task force consists of the steering committee and five subcommittees. The well planning subcommittee will focus on deepwater wellhead designs, shallow water flows and their mitigation, drill string considerations, mud requirements, severe weather conditions, when to secure for a storm or hurricane and the regulatory issues to be considered in planning a deepwater well.

The well control procedures subcommittee will examine shut-in procedures, balling formations, BOP stack clearing, dynamic positioning and conventional mooring systems, and kick detection and kill techniques. The equipment subcommittee focuses on BOP arrangements, riser design, riser configuration, how to handle riser gas, when to divert and different considerations with BOP control systems such as multiplex, discrete hydraulic and fast response hydraulic. The emergency response subcommittee focuses on pollution control and well intervention, and the training subcommittee will examine additional training above the current norms to address issues raised by other subcommittees.

"The guidelines that will result will normalize safety related procedural issues among operators and contractors," said Plaisance. "The guidelines are going to make us more consistent in the way we handle our operations. It is not our intention to mandate specific remedies, but to point out differences and highlight potential problems to be avoided." The task force intends to publish the guidelines for industry distribution in September.

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