Revolutionizing Deepwater Drilling

During the drilling of an oil well, crews set and cement in place a series of concentric pipes, or casings. These casings prevent the collapse of the geological formation into a well and also prevent potential leaks either in or out of a well. This structure results in a series of annuli (an annulus is the space between two concentric objects, such as between casing and tubing, where fluid can flow) generally filled with a heavy spacer fluid and/or packer or drilling fluid used to balance the pressure from the geological formation.

In the upper reaches of a deepwater oil well, casings are typically in a relatively cold portion of the geological formation (near freezing). The lower portions, where the oil is located, are as much as 25,000 feet below the ocean floor. These portions are extremely hot as a result of the natural geothermal gradient.

When crews first produce the oil well, the hot oil comes up from below, warming the whole casing string assembly (a long series of connected casings). Such heat causes the formerly cold drilling fluid in the annuli to undergo thermal expansion. In the industry, this phenomenon is known as trapped annular pressure or annular pressure buildup. The resultant pressure can lead to the collapse (or bursting) of the casing(s).

On land-based wells, crews can use a relief valve to manually alleviate pressure buildup. In deepwater locations, such valves are impractical, given that the actual wellhead at the sea floor can be as deep as 10,000 feet underwater. Moreover, there is no access to individual annuli, so it is not possible to relieve pressure simply through relief valves or through the use of a remotely operated vehicle.

Rather than rely on relief valves or other similar technologies that address pressure once it becomes critical, scientists at Los Alamos National Laboratory have developed a technology that avoids the problem altogether. The trapped annular pressure shrinking spacer, known as TAPSS, is a type of specialized fluid that shrinks—rather than expands—when heated. Such shrinkage eliminates the problem of thermal expansion, thus eliminating the issue of pressure in annuli.

To develop TAPSS, Los Alamos scientists worked with scientists from Chevron Energy Technology Company, Baker Hughes Incorporated, and Lucite International Ltd.

Oil Well diagram

Preparing TAPSS for Drilling

TAPSS uses methyl methacrylate, the same commodity monomer (a molecule capable of combining with other molecules to form a polymer) that makes the plastic used in latex paint, hot tubs, taillights, and giant aquariums. When emulsified into a water-based drilling fluid and placed into the appropriate annulus of an oil well, the microscopic monomer droplets polymerize into solid microscopic particles. This process reduces the volume of the methyl methacrylate droplets by 20%. When a drilling engineer determines the pressure requirements of a particular annulus, it is possible to calculate the amount of methyl methacrylate needed for the appropriate amount of shrinkage to compensate for any potential pressure problem.

TAPSS is mixed offsite and transported by an offshore supply vessel in large tanks. On the deepwater oil rig, crews will pump TAPSS from the tanks as a spacer into each annulus of the casing string that is being treated.

First the spacer is thoroughly mixed with an initiator; the completed mixture is passed to a high-pressure pumping unit, and the fluid is pumped so that it is placed in the desired part of the annulus when the cement portion of the process is complete.

When exposed to heat inside the annuli, deep in the well, the initiator triggers the TAPSS monomer's polymerization—and shrinking—process. The spacer is formulated with enough methyl methacrylate to ensure adequate shrinkage to offset the thermal expansion of all the fluid in the annuli.

Then, when the desired quantity of water-based TAPSS has been pumped, crews clear the line to the rig floor with water and close the valves on the manifold, thus isolating the high-pressure TAPSS pump skid. Crews then pump the cement down the drill pipe to seal the annulus and set the casing.

Revolutionizing the Oil Industry

Although seemingly simple, TAPSS stands to revolutionize the way worldwide oil industry drills and completes deepwater oil wells. By using TAPSS, oil companies might avoid pressure-caused oil spills, thus saving them the time and effort of repairing or shutting down such wells. Moreover, companies will avoid lost revenue as a result of unproductive wells.

TAPSS can also help eliminate the disastrous environmental consequences related to oil spills. Such spills cause both immediate and long-term environmental damage—some damage can last for decades after an oil spill. Oil spills damage beaches, marshlands, and fragile marine ecosystems. Spills destroy plants and kill marine life, birds, and even mammals. Moreover, the oil contaminates many fish and smaller organisms that are essential to the global food chain.

By making deepwater oil wells safer and less likely to produce an oil spill, TAPSS may serve as a catalyst in ultimately reducing the United States' dependence on foreign oil because it will be much safer to drill for oil off America's own shores.

As the world's reliance on oil as an energy source continues to grow, it is our responsibility to develop technologies that keep the oil-drilling process as safe and profitable as ever. With TAPSS, companies such as Chevron will be able to drill deepwater locations safely and cost effectively without having to worry about thermal expansion, which to this day has been the bane of the world oil-drilling industry because of its potential to cause casing failure that leads to catastrophic oil spills.

–Robert E. Hermes and Octavio Ramos Jr.

Oil ship photo

Drill ships such as the one shown here are used for exploratory offshore drilling of new oil or gas wells in deep water. The greatest advantage of such drill ships is their ability to drill at water depths in excess of 12,000 feet.

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