When installing oil and gas pipelines overland the preferred method is laying the pipe in a trench, but when the route crosses a body of water that preference changes.
Thanks to the advancement of navigation technologies, improved geotechnical engineering and improved drill rigs, the preference moves toward horizontal directional drilling (HDD).
How common are HDD water crossings for oil and gas projects? The first one was for Pacific Gas & Electric Co. in 1971 and since then they have become so common that Richard Levings, director of product management at American Augers, says that one of the company’s rigs is actively working on a water crossing every day, which is plausible considering American Augers is known as the river crossings company.
“We were one of the earliest large rig manufacturers and even our promotional tagline was ‘The river crossing pedigree,’ because we were one of the early manufactures of river crossing sized rigs,” Levings says.
Though water-crossing lengths vary, given the size of pipe used in the oil and gas industry, many projects require the use of midi- and maxi-sized rigs.
“If you are crossing a bay in Houston, that could be 10,000 ft and you will have to do an intersect, which will take two rigs, and if you’re doing that size of the bore, it will be very large pipe and you will press to the very largest edge of rig size,” Levings says. “If you are talking 3,000 to 5,000 ft of 30-in. steel, then you will be in the middle range of rig capabilities. If you are just crossing a river with 24-in. and maybe a 2,000-ft shot, you will move down to the lower end of the rig sizes. This is all driven by length, size of the product and the soil you are working with.”
Mark Kwilinski, senior engineer for Mears Group Inc., says his company’s projects frequently use two rigs for water crossings, a larger rig in the 1.3 million lb pullback range to drill the bore and pull back the pipe. On the opposite end is a smaller rig, in the 140,000 lb range, to act as a catch rig to deal with the tail string on the exit end of the bore and to assist with the reaming.
Overall, though, size is ultimately determined by what the project engineers expect to see in the ground formation.
“On the engineering side, we review each crossing we will perform and conduct an engineering analysis on the hole we will create and the pipe we will pull through it. Over the years, we have gone back to compare the results we observed in the field to our model of what we expected to see. As we complete that circle, more and more often, our model gets better and our ability to predict what will happen and therefore our ability to plan gets better every time,” Kwilinski says. For example, “On most significant bores we will do a hydro fracture analysis to predict what we will see for downhole pressures from the drilling fluid in comparison to what the formation can contain while we drill. We’ll plot that every step of the way while we drill and the more often we do that, the more predictable results we are able to get by adjusting our drill plan.”
Size aside, the rigs used for water crossings, as well as the bore itself, do not vary much from under land counterparts but, according to Kwilinski, what can vary is due in part to regulating agency guidelines. For example, he says a FERC regulated project may specify or have strict requirements on material coming out of the hole (cuttings) and backfill into the project area. On the environmental side, Mears may also have restrictions concerning drilling fluid additives or work hours to protect the marine species it will encounter during the crossing.
“With the HDD work, and this goes for any project, we’ll go through the formation and run calculations on the forces we expect to see both during the installation and post-installation. That is the normal process. We’ll review the profile for the radius, the bends, stresses on the pipes, stressing on our tooling like the reamers.”
Though bodies of water vary from small streams, to large rivers and bays, a quality navigation system is also key to a successful HDD water crossing. In the case of smaller streams, a handheld navigation system can be used but most contractors go with a DC or AC wireline system or the gyro method. Drill rig manufacturers do not offer the systems in-house but the rigs are built to accept any system.
“It really depends on the rig. If you buy an American Augers maxi- or midi-rig, everything is prepared for a wireline steering system, which is really the major thing you have to complete a water crossing,” Levings says. “Every drill that we manufacture has a collector ring or a commutator, and we wire it so they can clip the wire that is run through the drill pipe, to the commutator, which communicates with the computer and it collects the data from downhole.”
In Mears’ case, they go a step further by employing a steering supervisor who is dedicated to HDD navigation. “On the steering end, we employ someone whose sole job it is to manage the steering that we do on our projects. We dedicate a significant amount of resources, time and planning into the system we will use that makes the most sense,” Kwilinski says.
Other factors in water crossing steering include if the bore is in an active shipping lane. In that instance, it might not be safe for a diver to run a wireline system or the system might interfere with a ship’s navigation system so a gyro is used to guide the drill.
It is through increased accuracy with steering that HDD contractors have moved toward perfecting the HDD intersect method.
“The length of crossing determines the use of an intersect. As we get further and further out with a directional drilling rig it becomes more difficult to steer,” Kwilinski says. “Another deciding factor is if we are concerned with something in the formation and our ability to steer into a casing we will use an intersect to alleviate the problems.”
A lot has changed in the HDD world since that first water crossing. What was once thought of as impossible is now possible. As the advancements in steering, geotechnical data and HDD rigs improves, longer, and longer crossings are within reach.
Mike Kezdi is an assistant editor at Benjamin Media Inc. and a contributing staff editor of North American Oil & Gas Pipelines. Contact him at firstname.lastname@example.org.