Drilling & Production

Sept. 1, 1997
Sometime in 1993, while considering shale conversion and the suspension of slag in fluid until activated, Phil Rae wondered aloud if the same couldn't be done with cement. "Of course, you immediately heard ten reasons why it wouldn't work," recalls Rae's colleague, Dan Mueller. "But Phil went back and worked on it and came up with a method to mix cement, put it to sleep, and then some time later - a week, a month, later - activate it and have it harden and assume properties

Cement: pump now, activate later

Sometime in 1993, while considering shale conversion and the suspension of slag in fluid until activated, Phil Rae wondered aloud if the same couldn't be done with cement. "Of course, you immediately heard ten reasons why it wouldn't work," recalls Rae's colleague, Dan Mueller. "But Phil went back and worked on it and came up with a method to mix cement, put it to sleep, and then some time later - a week, a month, later - activate it and have it harden and assume properties consistent with Portland cement."

The fruit of Rae's efforts, dubbed "Liquid Stone" by BJ Services, was put to its first field test in 1995 by an Australian operator who needed a cement job, but not badly enough to pay the rent on $750,000 worth of mixing equipment. According to Mueller, BJ's man in Singapore, "cleaned old tanks and went in with Liquid Stone mixed before being transported to the rig and pumped the job with on-site equipment."

Since then, it has been used on more than 50 jobs in and around Indonesia and recently to staunch a blowout off Taiwan that had raged at about 40 MMcf/d for nearly a year.

Though it has obvious, significant weight disadvantages in transport, under the proper conditions, liquefied cement also has distinct advantages over traditional dry cement. Since it is mixed in a laboratory setting, at relative leisure, rather than in the harried "on-the-fly" mode of the rig, quality control is easier.

Also, since it arrives on location with all additives in mixture, Liquid Stone can be pumped using rig pumps and at considerably higher rates than traditional slurries whose pump rates are limited by the speed with which additives can be effectively added. Control of the Taiwan blowout, for instance, was made possible by rig pump rates equivalent to three cement pumps at 18 bbl/min - an impossibility in the available space.

The mixture is kept in the liquid state by retarders, and is time and temperature sensitive or can be brought to harden with activators depending on the application. If properly formulated it can be set to harden at depth or in a prescribed time without activators. How long Liquid Stone may be kept in the liquid phase has yet to be defined. To date, BJ has kept it in slurry form as long as three months.

Since it need not be accompanied by pumps, additives, and silos, Liquid Stone leaves a smaller footprint and requires smaller capital expenditure than conventional jobs. It is also meterable and can be dispensed to location in small batches for such applications as external casing packers, as is being done in the North Sea.

Multilateral re-entry - with a difference

It seems no matter the operation, with the addition of the adjective "subsea," the technical challenge clicks up a notch or two. Often, that is a function of the vertical and horizontal movement inherent in the semisubmersibles and drillships from which the work is done.

Milling is especially sensitive to the influence of rig movement.

The ability to eliminate the effects from the ship's rise and fall is pivotal to accurate placement of a casing window for instance, which, in turn, is critical to any sidetrack plans. In a late-July press release, Halliburton and Norsk-Hydro announced successful re-entry of a Troll Field (North Sea) well to install a lateral with full lateral liner connectivity, a hydraulically isolated lateral junction, and full-bore lateral re-entry access with a single casing-size reduction.

Such laterals are not groundbreaking in themselves. A number have been placed around the world by Halliburton and others. The interesting technology in the Troll job, mentioned about four paragraphs into the Halliburton press release, is in the form of a reference to "its milling technology partner, Weatherford Enterra."

The difference between earlier such lateral installations and this one, which made it newsworthy, was the fact that it was a re-entry of an existing subsea completion. That meant success hinged upon a window precisely milled from a floater, which is hard to imagine without elimination of the aforementioned vagaries of drilling vessel movement. Enter Weatherford Enterra's Rate Of Penetration Control (ROPC) tool, developed with just this project in mind.

Landed on the subsea wellhead wear bushing, the device eliminates weight-on-bit variations. It then controls ROP through a group of flow regulators located in a main, upper-cylinder that maintains a constant-volume as a pressure contre temps to rig heave. A lower, secondary piston is designed to ease the mill back into position when the tool is being replaced after being moved off bottom for any reason.

The overall significance of the Troll success is that the promise of multilaterals is now available to an entirely new market. According to Ali Daneshy, Halliburton's vice president of Integrated Technology Products, this includes "the potential to reduce by one-half the costs associated with subsea developments by reducing the systems required to access the reservoir." That is a considerable amount of money in the capitol-intensive world of subsea E&P.

Yet another platform design

According to a press release from Aker, the Oslo-based engineering giant, it has developed and is ready to build, a new type of floating platform that will make the difference between uneconomic and economic in some small offshore fields.

Favorable economics are partially derived from the vessel's compactness and mobility so that, as with FPSOs, it can be easily moved to a new location once a field has been depleted. Called Buoyform, Aker insists it can build the floater in 23 months at about NKr 500 million less than comparable platforms.

The design centers around a conical storage tank that floats beneath the sea surface, and a deck with living quarters and process equipment. With an 83-meter diameter and 400-meter draft, its designers say the shape and size combination lend it smaller and calmer motions than either a production ship or a semisubmersible platform.

Requiring no mooring lines or riser turret, the vessel is held in position with conventional anchors. It can be delivered as combination drilling, processing, and storage vessel or as a pure drilling rig. Equipment exchanged to accomplish the desired configuration is done, say its designers, with relative ease.

Statoil has participated in the design's development and various undeveloped Statoil fields have been used for evaluation purposes. Evaluated solutions include production capacity of 60,000 b/d and storage of 570,000 bbl.

Maritime says it could build the hull in its recently purchased Aker Mantyluoto yard in Finland. Aker subsidiaries Maritime Tenteck and Maritime Trosvik were the developers of what is essentially a refinement of the Big Buoy concept Trosvik launched in the late 1970s based on an Aker Maritime spar patent.

Wanted: get out of trouble stories

New ways of thinking, attacking problems from a fresh angle, are what has taken offshore exploration and development from a moribund industry to a booming one. Innovations - broad-based ones like alliancing, and more specific technical ones like multilaterals - have taught the industry to do so much more with so much less until, as one wag long ago put it, "we have learned to do almost anything with nothing."

But beyond these highly visible achievements lie the small victories that get no press (indeed press is not always deemed a good thing when one is resorting to such measures). Some of these triumphs are the result of quick thinking, inventiveness, or the use of obscure or barely developed techniques. Some are the result of using ideas as old as the offshore oil and gas industry itself in a some new way.

Big innovators have PR and marketing managers whose job it is to make certain the trade journals hear the big stories. (It is a symbiotic relationship: they get ink for employers; we bring usable information to readers; everyone gets a paycheck).

But, it is often the small story that teaches a large lesson. Once in a while, over a lunch or coffee we hear a bit. Now we want to hear more from our readers, friends, and colleagues who have found themselves reaching into their bag of experiences to pull together some innovation that is just the right solution to some drilling, completion, production, or other problem. Sometimes they are called war stories, but they often are the best way to teach - particularly in an industry that has lost so many greybeards lately.

If you know a tale, tell it to us in your own words and if our editors think it contributes to the pool of knowledge or is just a good story, we'll get it out. Think of us as your PR agency. Send your stories by email: [email protected]; or by mail: Rick Von Flatern, 3050 Post Oak Blvd, Houston, TX 77056; or phone at 713-963-6213. (Legal disclaimer: No guarantees about anything).

Copyright 1997 Oil & Gas Journal. All Rights Reserved.