Q: Why Civil Drilling(CD)? Aren’t conventional trenchless utility rigs sufficient?
A1: Conventional slant rigs and horizontal rigs in civil construction are too small for many of the projects requiring CD directional drilling.
A2: CD rigs are focused on deep and relatively small-bore laterals, but drilling very quickly, cheaply and accurately.
A3: The plan is to use the desperate need overseas for rapid utility installations in Raqqa, Mosul and elsewhere to return these cities to full function. Basically, we’re doing the USACE (US Army Corps of Engineers) work. Just better, and much, much faster.
Q: There are plenty of rigs out there now that drill large bore laterals. Why CD?
A2: Those laterals cost from $700-$1,100/foot, minimum
A3: The methods noted above take more time and are far more difficult to stage than CD.
A4: CD Laterals start at $100/foot and the price goes down from there.
Q: What is the maximum lateral for a CD rig?
A: About three miles now, about 6 miles with modifications.
Q: How much time does it take to drill a three mile lateral?
A1: 3 to 6 days.
A2: This looks slow, 1.5 to 3 days may be typical as rig development progresses
Q: How much does it cost to drill a three mile lateral?
A2: About $100/foot, or less.
A3: This seems to be getting cheaper with the single pass, but the pipe will remain in the hole, so that cost needs to be considered.
Q: What is the maximum bore and distance of CD?
A1: Maximum bore and distance are anticipated to match the largest land rigs in the oil sector.
A2: 8” to 12” is the design OD for most purposes.
A3: For now, 9 5/8” is the Basis of Design.
A4: Increasing bore/diameter beyond range 3 pipe is in process
Q: How does CD make drilling cheap enough to be efficient?
A: Drilling with Casing (DwC), which makes single pass drilling efficient (See Single Use Drill Bits below)
A2: CDX Daylights all passes, which means that Reamer Runs (and additional pipe diameters and more cost/time) are possible.
A3: Reamer runs need to be revisited. From a marketing standpoint, being able to pull a larger diameter pipe is a plus.
Q: How exactly does a CD rig maintain weight on bit (WOB)?
A: Enormous hydraulic jacks.
Q: What utilities are planned for CD?
A1: First utility uses will be water and sewer line installations in remote and unserved/underserved areas.
A2: A second utilization has been identified but not yet developed in electrical utility transmission. Think hurricanes, floods, and storms. Shallow trenchless has proved to be vulnerable to flooding, and we all know what happens to electrical systems in hurricanes. DEEP trenchless (CD) is immune to those interferences with service.
Q: Can CD drill for other utilities?
A: Yes, in general, CD works for any type of utility installation including power, and fiber optic cable.
Q: Could CD be used to install pipelines for fuel, crude oil, or gas?
A: Yes; further, CD was originally conceived of to build secure fuel lines in hostile environments like Afghanistan. DMM
Q: Why don’t you use a Coal Bed Methane (CBM) rig?
A1: In actual practice, CBM rigs are small-bore and distance rigs without sufficient horsepower for extended reach horizontals to the extent needed by CD. Torque and drag build up and expansive BHA tools get lost, resulting in expensive fishing efforts. Everyone gets upset, and the bills on extended reach CBM drilling are extraordinary. DMM
A2: CD rigs and processes are designed to scale up in size and distance; every advance in lateral bore size and lateral reach is a step toward the next scale up in the CD model, until all of the current limits of technology are reached, and the torch is passed to an adjacent team in materials or applications development. (“Moore’s Law goes underground”)
A3: It is important not to over-promise here, there are some very important upper limits in lateral diameter, often related to the differing conditions that CDX rigs drill through. When we reach the upper limit, we need a new tech break-through.
Q: Are you really able to drill to daylight?
A2: Yes, BUT NOT DESIREABLE, due to lost circulation. Once fluid no longer circulates, drilling has effectively ended.
A2: Bottom Hole Assemblies (BHA) recovered at the termination with a drop well, and ‘Single Use’ BHAs may change that process.
A3: Reamer runs may play an important role in whole city utility development.
Q: In these proposed drilling areas, what information is available from borings, seismic 3D, etc.?
A: Generally, almost none. On occasion, some, but exploratory is often expensive and dangerous.
Q: Then man-made or natural obstacles can clearly cause problems for CD.
A2: But, look at Big Bertha in Seattle. If CD had been used to pin-cushion the TBM trajectory, the interference would have been found with ordinary downhole instruments.
A3: The focus going forward is to both detect obstacles, and to steer around them in real-time.
Q: If you have no information about existing and expected conditions, how do you plan to build laterals in the unknown conditions?
A: The CD strategy is to use a generalized model from all available data to understand expected conditions, then plan a drilling strategy, then execute a completion strategy based on the worst possible expected conditions.
Q: That would never work in the oil industry.
A: We are not in the oil business.
Q: Where is the water table in CD models?
A2: Rule Number 1: Expect water.
A2: Rule Number 2: If there is no water – inject water.
A3: Air/water drilling fluid models may be the most desirable.
MECHANICAL ENGINEERING Questions
Q: What is the design operating pressure on a CD water supply line?
A1: 1,500 psi
A2: Overcomes some, not all, of the small pipe bore issues.
Q: How is that possible – most water supply mains work at 200 – 300 psi as the absolute max?
A1: Deep bury.
A2: Surrounding earth support.
A3: Cement squeeze jobs that secure lines beyond their usual operating pressure.
Q: What about the risk of seismic events breaking brittle, fully-fixed pipes in place?
A1: At least two solutions are available.
A2: Fully fixed lines can be re-drilled, because once the CD rig is in place, it never leaves. Re-entry.
A3: Lines are left in loose and consolidating material at depth that allows for flex in the final pipe.
Q: The rig stays in place forever? Why?
A1: Workovers. Re-enter any lateral for any reason, when necessary, at full power.
A2: If new lines are needed, the CD rig is in place. Plan – spud-drill-complete.
Q: How does a sewer system deal with gravity if the line changes direction?
A: CD doesn’t use gravity. Gravity is an uncertain and difficult tool in developing effective supply and collection systems.
Q: Not using gravity is unusual and disruptive in water and sewer construction, isn’t it?
A: Force mains collect to local pump stations via gravity lines, then pump wastewater under pressure with macerating pumps.
Q: CD relies on Pump Stations and Force Mains to collect wastewater, correct?
A2: CD at first uses central plant suction pumping to collect wastewater, not distributed lift stations. If you have seen headers on a well-point dewatering system, you understand how CD works with central vacuum collection management.
A3: RD brought up the problems with suction pumping for wastewater management, but we cannot address this, in CDI we build good lateral pipes quickly.
Q: Without macerating pumps at the collection points, won’t small-bore debris clog the collection laterals?
A2: Successive trash racks in drop wells will be installed to limit trash size, and effectively filter wet waste. And yes, the trash racks will need to be cleared periodically. Keep in mind, however, that trash size is limited by the diameter of the lines to the drop wells.