The alternative To Hydraulic Fracturing
Fracking for Oil is expensive and it may disrupt and pollute the environment.
At Carter Tech we have found the solution to both of those problems with our Slot Drill method.
Problems and solutions For Hydraulic Fracturing:
- Costs too much
- Leaves a lot of oil behind
- Not applicable to all places
- Not so environmentally friendly
- Politically unpopular
- No current alternative
– Environmentally friendly
– Works in more places
– Scalable small to large
– Not just an incremental improvement
– More oil per acre
Stimulating Gas & OIL Shale Without Hydraulic Fracturing
The SlotDrill™ concept is a new way to Gas & Oil Shale, Coal Bed Methane, and Tight Sands.
What’s wrong with Fracking?
“We control everything about fractures except where they will go and how thick they will be”
- Hydraulic fracturing uses tremendous resources of water and equipment
- Hydraulic fracturing is expensive an unpopular with some land owners
- Lots of gas is left unrecoverable
- Reduced water requirement
- Prevent aquifer pollution from breakout into adjacent water strata
- Reduced potential to damage water wells
- Recover more gas per leased acre
- Reduce environmental footprint
- Reduce costs
Instead of hydraulic fracturing we plan to mechanically cut an 1 to 3-inch-wide slot outward from the well bore hundreds of feet into the formation along a substantial section of the well thousands of feet long. This will provide a high conductivity pathway through the shale layers and back to the well bore. We plan to use a diamond abrasive cable saw to cut slots having a million square feet of formation surface area in just a few days of sawing.
There are two competing hardware designs,
the U-style and the J-style. The U-style shown below works like a rope saw and is less complex than the J-style because it requires no special downhole tools but it requires a longer hole that angles back to the surface. Can be operated by drill rigs or rig and a large crane or just two cranes.
U-Style system operation
- Both wells completed and cased down to the area where slot to be cut
- Tubing is inserted to end of casing
- Cable is and secured to top of tubing at each end
- The two tubings are reciprocated by cooperation between the rigs
- Cable is periodically advanced to expose fresh cutting surface
The J-Style concept works in a blind hole sort of like a down-hole Hacksaw.
J-Style SYSTEM OPERATION
- A diamond abrasive cable is the blade. The drill pipe is the frame and is reciprocated by the rig raising and lowering the drill pipe.
- The cable is attached at the tip of the drill pipe and at a proprietary tensioning device on the pipe above the area to be cut.
- The cable tension presses the cable into the inside radius of the curve.
- The hole may be cased with fiberglass casing and the cable will slice through it.
A cable release tool on the end of the drill pipe can be activated to release the end of the cable when the cut is complete. If the cable should break this also allows the pipe to be pulled back and loaded with a new cable to begin a cut with a new angle off the bore. The portion of the bore hole past horizontal may turn sideways instead of upwards.
Tuned Pulse Gas Slot Frac
Once a large slot has been constructed it may be possible to extend the slot by initiating a fuel/air explosion within the volume of the slot.
Air is pumped into the slot to displace all fluids up the pipe. Natural gas is permitted to fill the slot. Additional air and accelerant is added to create a combustible mix in parts of the slot.
The mix is ignited to create a very rapid pulse of overpressure within the volume of the slot itself so it will apply millions of tons of force against the sides of the slot and produce multiple simultaneous fractures in the face of the slot.
- Huge water savings
- Fluids not injected into formation
- Aquifer protection
- Positioning Accuracy
- Reduced equipment – engine emissions
- Slots can be directionally steered to recover more gas from the same lease acreage
- Multiple slots stacked side by side or radiate each direction from single vertical well
- Reduced environmental footprint
- Lower costs
Slot Drill Technology Provides Complimentary Alternative to Hydraulic Fracturing
A Houston-area engineering firm is developing a viable alternative to hydraulic fracture treatment.
The Slot Drill concept phase was conducted as part of the US Department of Energy’s Research Partnership to Secure Energy for America (RPSEA) program, by Carter Technologies in collaboration with M-I Swaco, Younane Abousleiman of the University of Oklahoma Mewbourne School of Petroleum and Geological Engineering, and Peter Valkó of Texas A&M University’s Harold Vance Department of Petroleum Engineering.
“It’s essentially a way of effectively coupling a well to a formation,” said Ernie Carter of Carter Technologies. “The intriguing thing about this is, it does not require the huge amount of resources needed for fracturing—it is essentially done with the power of the rig itself. It doesn’t require fifty million dollars worth of service company equipment on location. And it doesn’t require the vast quantities of water, and the vast trucking resources, and the vast pit resources needed for fracturing.”
The Slot Drill system uses large-diameter wire rope as a saw to cut a 1 to 3 inch thick pathway through an underground formation. The idea is to create a football-field-size slot connected directly to the well bore.
“And rather importantly, it’s not a random process. When we fracture, we may think we know where things go, how wide or how long the cracks are, but we never truly know,” Carter said. “In many shale plays, we only get a fraction of the fracture water back, and we have no idea where the rest of it went.”
The location of a slot can be selected and more precisely placed than a hydraulic fracture treatment, and the slot is much thicker so we get much higher conductivity than a fracture. The slot drilling can be done in a grid, creating a slot matrix in which there is a slot within a fixed distance of every place in the formation, with slots that are all precisely oriented with known geometry.
“I think of the slot as analogous to freeway superhighway loops in the city—they move traffic much faster than regular streets,” Carter said, “exposing every bit of that formation to the low pressure of the wellbore—it allows you to expose a huge cross section of the formation to the full pressure drop of the wellbore.”
The slots can be drilled flat, vertical, twisted like a ribbon or curved like a scimitar. Hydrostatic pressure holds them open as they are cut and gravel packed. “We could even use pea-sized gravel, instead of more expensive fracturing sand. Drilling with a gelled brine—we don’t have to worry about formation damage from our drilling fluid, and we recycle all the drilling fluid to the next well” Carter said. “You do need a larger mud system than just for drilling, three times the volume of what it just takes to drill the well, but M-I Swaco has very excellent equipment to handle that.”
The Slot Drill technique has two basic approaches: the “U” style (with two openings at the surface) and the “J” style. Carter said the blind-hole “J” style will likely be preferable in the future because it is cheaper to drill. Nevertheless, the “U” style is the best bet for early adoption since it is mechanically simple and more suitable for coil tubing. The initial drilling of the “U” style involves directional drilling a hole either all the way back to the surface like a river crossing or meeting another hole underground.
In harder rock diamond abrasive beads are added to the wire rope to increase productivity. Smaller diamond-equipped wire ropes have been used for nearly half a century to cut stone in the rock quarry industry, having been applied to very hard stones such as granite, where thin, precision cuts are needed to prevent wasting valuable rock. “Most of the diamond beads are no longer made in the US, but I have one vendor who says they can manufacture the 1.5-inch or maybe 2-inch diamond beads, no problem,” Carter said. “We have extensive data on cutting rates from the quarry industry, so we have a pretty good idea of the cutting rates that can be achieved.”
Comparing Two Methods
For the concept phase of the Slot Drill project, Valkó used a specialized modeling technique called “Method of Distributed Volumetric Sources” to compare the productivity of a slot drilled well to that of more traditional well-fracture configurations. The modeling technique itself provides the overall productivity index both in transient and pseudo-steady state flow regimes (as described in paper SPE 120110). Since the modeling effort we have found that it should be possible to cut slots with many times the surface area of those modeled. It now seems probable that slots can expose up to a million square feet of formation surface. This is similar to the magnitude of a small frac job but at a quarter the cost.
With hydraulic fracturing, many factors determine the resulting geometry and, ultimately, the overall productivity of the well-fracture system and some of these factors (such as in-situ stress state and pre-existing plane of weaknesses) are difficult or impossible to control during the treatment, Valkó said. One potential advantage of the Slot Drill approach is creating a desired sink geometry and orientation, which he said can ensure maximum communication with natural fractures, for example. Also, slots can be spaced more freely than fractures, if the formation properties require it, he added. “They have great potential in establishing desired flood patterns,” Valkó said.
Another complex issue regarding hydraulic fracturing is the resulting conductivity distribution within the created fracture that might result in loss of productivity. With the Slot Drill technology, a potentially “infinite conductivity” sink can be created, assuming the implementation of a proper method to keep the slot open, Valkó said.
Why an Alternative?
“This can be extremely advantageous, for instance, for completing wells in higher permeability formations,” Valkó said. “However, I do not consider Slot Drill technology and fracturing as rival techniques. More likely, they can be used in combination. In such a case fracturing could do what it does the best: providing additional communication into the bulk of the formation, but with less materials and energy spent on establishing the intermediate connection to the wellbore that might be achieved more effectively by the Slot Drill technology. In that respect, Slot Drilling might also help in making hydraulically fracturing more environmentally friendly.”
There would be a receptive market for such an alternative or accompaniment to hydraulic fracturing, in various places for various reasons, said Abousleiman, director of OU’s integrated PoroMechanics Institute (iPMI), who also reviewed the technology’s concept proposal and was involved its initial submission to RPSEA. Environmental regulations related to fracturing treatment make such an alternative potentially very enticing—for example, in France, hydraulic fracturing has been completely prohibited, and Germany is likely to follow suit, Abousleiman said. In the US, hydraulic fracturing regulation likewise remains undetermined in various jurisdictions.
“In his technique, permeability damage does not exist, because we’re not adding any additives or fluids, we’re not putting in any chemicals,” Abousleiman said. “It could open up markets that may be otherwise closed for the next 50 years.”
The Slot Drill technique also avoids complications and uncertainty stemming from interaction between fracturing fluids and the relatively high and chemically active clay content in shale formations, Abousleiman said. This is of particular relevance for example in the Marcellus shale, where the shale content is particularly high, Abousleiman added.
“With the engineering technology that we have today, even though we have improved our engineering, we have not improved our rocks,” Abousleiman said. “What Carter is putting on the table, he is saying there is another technique, you can control how far you drill your slot, and it is a permanent fracture. There is no closure on that fracture, it’s not fluid cutting—let alone, he has no water damage.”
The RPSEA funding for the Slot Drill concept phase came in 2009. At that time, the conceptual framework focused on gas shale, but there has since been a growing industry interest in liquids-rich shale and oil shale, for which the method can also be applied as an important complimentary alternative to fracture treatment. Beyond that, the method also has potential applications in geothermal drilling, artesian wells, and carbon capture and storage projects, Carter said. The company is currently in negotiations to license the technology non-exclusively.
“We were essentially asked to take a clean sheet of paper and come up with a new way to reduce the amount of water necessary to stimulate shale gas and also to reduce the net environmental footprint,” Carter said. “At the time we were specifically asked to think about shale gas in the 6,000-ft-to-12,000-ft range, which is what the market was thinking about at the time. Upon further consideration, we are thinking that probably the sweet spot for this technology would be coal bed methane, and areas that have a very thick strata of producing zones that are not very deep.”
Packaging the Technology
The technology would be best marketed and implemented as a field service package, Carter said.
“The tensioning devices for the “J”style go downhole. A component of the system would be marketed as a downhole tool. Ideally you would sell it like you sell directional drilling services,” Carter said. “I worked designing downhole tools for my first seven years at Halliburton, so I have more than a little bit of experience at what can actually be made to work as a downhole tool. It’s a separate art. The hardware itself is very simple and robust, but it has to be very clever, it has to be very mechanically simple to survive the downhole conditions. Almost always it’s got to have a tremendous amount of tensile strength. Downhole tool makers typically have an outside diameter and an inside diameter, and the rest area variables. The tools that are out there now are better than what we had 20 years ago, and the electronics are way better than the tools we had 20 years ago.”
“Current (fracture) technologies can recover less than 10% of the hydrocabons in a given acreage, so if this increased even up to 13%, it’s a 30% increase in total recovery,” Carter said. “If you can get a slot within 100 feet of all the producing formation rock, rather than have it go out randomly and missing a bunch of areas, your chances of going from that 10% to 13% are a lot better.”
Such an improved recovery technique also has potential implications for heightened reserves assessment. Furthermore, this technology is different than many new technologies now coming to market because of its simplicity and conventionality, Abousleiman said. “We need to think outside of the box. This thing gives us another opportunity of what I call large scale mechanics operations,” he said. It does not require scrutiny at the nano-scale level and “we don’t have to worry about whether the fluid at the tip of the fracture or is the fluid 1,600 yards away,” Abousleiman said.
This technology is available for license.
Carter Technologies Co
9702 Garden Row Drive
Sugar Land, TX 77498
Phone (281) 495-2603