ADVANCED DRILL WEIGHT REDUCING METHOD FOR GEOTHERMAL ENERGY EXTRACTION USING TAPERED SOLID CONICAL DRILL
C. Balaji Krishna Kumar*
Department of Mechanical Engineering, Bharath University.
ABSTRACT
Energy efficient drilling technology for water wells, oil and gas wells and geothermal wells is a present need. Generally, either percussion or rotary type of drilling is used for drilling. This system combines both rotary and percussion type of drilling. Experimental test shows tapered solid drill bits drills the concrete and rock more efficiently than the grinding action of the present drilling technology.
Geothermal well drilling is designed using hydride carbide and diamond tapered drill bit with a suspension system to reduce the weight. This drill can drill the Earth’s crust to 5-25 kms to extract energy from hot rocks at 700°C. In order to avoid subsidence a container is fitted after completion of drilling and water is injected into the vessel for producing steam.
Geothermal energy extraction requires reservoir for generating steam. Geothermal energy production requires mainly a reservoir, though there is thermal gradient, it is not tapped. So, an innovative way to solve this problem is provided. This system is energy efficient than any other drilling technology such as plasma or thermal spalling and will only be the answer to all our energy needs in the future.
Key words: Drilling, Advanced drilling system, percussion and rotary drilling, energy efficient drilling, drill weight reducing system.
1. Introduction
Geothermal, Oil and gas well drilling technology use Tricone bits and diamond coring bits. Water bore well drills use flat rock drills. All these drill bits use grinding process for drilling. In this paper, these drills are replaced by tapered solid drill bit which provides faster and energy efficient drilling.
With the present geothermal drilling technology, drilling after 20 kms can create seismicity if the load of the drill acting at the depth is of the order of 25000 T, though the weight is supported by the mud and debris in the present slim hole drilling technology. Drilling with robot type remote operation can be used only up to certain depth since there may be blow out of the robotic drilling system due to less weight and high pressure acting against the equipment weight due to high temperature and pressure at higher depths. So, a weight reducing mechanism is provided. This mechanism is safe and will not kinder the tectonic plate movements or seismicity. At 25 kms depth, vibrations produced due to the drill will be less than Secondary velocity of 3 m/s. Thus it will drill even at 25 kms. Diamond embedded Tapered drills is very effective in drilling hot temperature rocks.
In order to drill effectively, mechanisms have been designed in this paper. Diamond embedded circumferential drill suspension mechanisms and circumferential drill mechanisms at an angle are employed at places where there exists huge reservoir or void in order to hold the container.
The drill geometry is automatically modelled and meshed with the aid of NASTRAN NX- FEMAP program.
2. Methodology
At a depth of 15 kms or more, this weight reducing system will reduce 10000 tons acting on the drill bit. If 10000 tons act on at that depth it will cause seismicity. Only the required 10 or 15 tons will act on the hot rocks to drill.
Figure 9 shows the Driving mechanism which is a replacement of a rig type controls for drilling. This consists of springing suspension mechanism as shown in the figure to handle hammering action. Hammering is mainly needed to break especially granite rocks by impact loads.
In geo thermal drilling the weight of the drill with the series of drill pipes is of the order of thousands of tons. Hence, slow drilling process with very high torque values is used for drilling. Figure 2 shows the Drill weight reducing system in front view. This consists of spring or steam jacket for hammering action. The weight holding rod consists of two parts; one part is fixed to one end of the spring or steam jacket and other end moves into the circumferentially drilled ring by means of a cylinder.
The suspension system uses steam cylinders attached to the container and Drill weight reducing rods. Using gear drive mechanism, shown in Fig. 13, the drilling is carried out along the circumference. This mechanism is supported and powered by the drill pipe and this provides a sturdy operation. After drilling, the circumferential drill bit has to be retained between the rocks after penetration to maximum depth. After drilling the first part, the second part of the circumferential drill is brought by the movement of the ladder along the tracks from the surface and it is connected to the first part by the circumferential drilling mechanism. Usually a drill bit is three or four parts connected together depending on the depth required to hold the weight of the drill pipe. After drilling to a certain depth (assume 25m) the first set of circumferential drills is placed and weight reducing rods are inserted into the ring of the circumferential drill bits. Again the diameter 1 m drill bit drills to 25 m and the ladder moves the first set of drill weight holding rods to the next 25 m after drilling circumferentially. The pneumatic jackets compress and elongate based on air flow adjustment of compressed air in pneumatic cylinders through pipes. The flow of pressurised air is controlled by flow adjustment valves. This produces hammering action and drilling is completed to further depths.
After drilling to 10 kilometres the temperature and pressure of the system increases along with the depth. This pressure is blocked by the weight of the Solid tapered drill bit and blow out is prevented by the circumferentially drilled weight reducing system.
For each depth a set of container is moved forward using the mechanism shown in Fig 9. In this mechanism, drill pipe is fixed with bearings and suspended over the springs. A set consisting of mud fall blocking pipe, drill weight reducing rods, and the drill pipe is inserted together for a calculated depth each time. Where, holding plug is detachable. So, for every increase in calculated drill depth, holes are created at an angle along the circumference of the mud fall blocking container for a calculated distance into the drilled hole through rock drill bits. This is done in order to prevent entire weight of the drill pipe, of length 15 kms or more, to act on the drill bit.
Three set of containers are fixed to the ladder system shown in fig. 9 which are suspended by springs to the gears based on the weight against free fall and the ladder can move on tracks through the entire depth as shown in Fig. 5. The ratchet and pawl mechanism, pawl with springs prevent the ladder from freefall and holds it on to the tracks. The pawl releases the gear only if the spring force is exceeded by the engine. While the ladder is moving upwards it moves freely. This mechanism is shown in fig. 8. During circumferential drilling the ladder is fixed to the stops on the container.
After drilling to certain depth using the 1 m drill, holes are drilled to the circumference and containers are moved and placed using the mechanism shown in fig. 9. Then the first set of container is moved by using the ladder system so it releases the first set of springs. This makes the other set of springs above the container compress. The container is first fixed to the ladder and locks are detached for the first container to move freely. So, the first container advances into the depth and is made to seat on the already drilled circumferential drill pins. Similarly the next set of containers is moved in to the depths. For 10 Km, 10000 containers are required. After drilling to certain depth each container is moved and placed on the circumferential drilled weight holder pins.
The lead part of the drill is made sharp with a diamond tip and the body has steps of various diameters. Carbide buttons with diamonds are brazed along with High-speed steel drill body. The drill can be two fluted or three fluted. Three fluted drill are more advantageous than two fluted. Coolant for the drilling operation is provided through a separate hose. Suction of debris after drilling is done through the drill pipe. After a certain depth the debris comes out and is sucked through the drill pipe.
Cementing and grouting is not essential but can be used if necessary after drilling certain depth.
Geothermal zones have a temperature starting between 500°C to 1000°C. Generally, even 20-25 kms depth can produce high geothermal zones even without reservoirs. Cryogenic technology will be required to cool the drill and its mechanisms are at very high temperatures and pressures, beyond 25 kms.
3. Placing of container in voids or gaps
The drills are drilled at a certain angle for penetration into the top and bottom portion of the void or reservoir using the mechanism in Fig 14 and Fig 15. Then the container is attached to the holder pins using connectors as shown in Fig 16.
4. Thrust and torque
The thrust ball bearings are used for carrying thrust loads exclusively and at speeds below 2000 rpm. At high speeds, centrifugal forces cause the balls to be forced out of races. Therefore at high speeds it is recommended that angular contact ball bearings should be used in place of thrust ball bearings.
5. Springs
A concentric spring is used to obtain greater spring force within a given space and to insure the operation of a mechanism in the event of failure of one of the springs. A concentric spring for drilling is to exert a maximum force of 5000 N under an axial deflection of 40 mm. Both the springs have same free length and are subjected to equal maximum shear stress of 850 Mpa. If the spring index for both the spring is 6 then design for the load shared and for main dimensions of the spring including number of active coils in each spring.
6. Calculations
Weight of the container
Weight per metre length of a 10 mm thick container = 248 Kgs.
Weight of 10 mm thick hollow drill pipe of 150 mm diameter for a 1 metre length = 200 Kgs.
For every metre depth 500 Kgs load of container and drill pipe is balanced by the weight holding system.
So for 10 Km, 10000 containers are required.
Weight based on volume at depths
Weight based on depth can be calculated using the system shown in Fig 1.
Water content = (W-Wd)/Wd
Bulk weight = W/V
Dry unit weight Xd = X/ (1+W) = Wd/V Also, Xd = G. Xw / (1+e)
Vw = Ww / Xw
Vs = Ws / Xs = Ws/g. Xw
Vv= (V- Vs)
where,
Volume V, Dry weight Wd, Wet weight W and Specific gravity G.
For Earth’s density of 2000 Kg/m2,
The depth required to be drilled circumferentially is 3 m using 10 cm diameter drill. This depth can take a weight of 500 Kgs for 4 m length.
So for 20 Kms weight of 5000 T, the number of circumferential drills required is 100, 000 at approximately 4 metre gap.
Results and discussion
This system of drilling is faster than the conventional drilling technology, at the same time a 1 metre hole is created instead of one 6 inch hole. Hence this drilling methodology is cost effective and produces more steam than the conventional geothermal drilling. One hole of 1 metre is equal to 10 holes of 6 inches diameter in present drilling technology.
This type of drilling is possible even without a geothermal reservoir. The diameter of the geothermal drilling hole can stepwise starting from 10 metres and then to 7 metres and then reduced up to 1 metre. At certain places 10 metre diameter can be constantly used for drilling without stepwise reduction up to certain depth.
This type of drilling with 3 metre diameter and 10 foot long drill can replace 30 times by size, the drilling using slim hole drilling technology. This mechanism is effective than the present rigs. To extract energy it is required to drill to certain depth till the life of the parts of the drilling mechanism does not get affected. After the zone is cooled then again drilling can be made to higher depths. This mechanism works as sturdy as the circumferential drilling mechanism even at any temperature and pressure more than 1000 ˚C and 1000 bar pressure. This design is more efficient and durable than the present technology.
Thermal insulation for the initial few kilometres depth will make the design more efficient. Insulation for various regions of container for the initial 5 km would prevent heat loss.
Thus this system reduces cost, time and labour in completion of well construction.
References
[1] Dr. William C. Maurer, Novel drilling techniques, 15-105 pp.
[2] Bent Sorenson (2004), Renewable energy, third edition, academic press, Elsevier Inc. pp 282-289.
[3] Drilling data handbook and practices manual, Oil and Natural Gas corporation of India pp.
[4] Gene culver, Geo heat center, Klamath Falls, Oregon, “Drilling and well construction”, pp 129-164.
[5] John Rowley, Seiji Seito, Roy Long, Advanced drilling system for drilling geothermal wells – an estimate of cost savings- World Geothermal Congress 2000, pp 2399-2404.
Figures:
Fig 1 Weight based on volume at depths.
Fig 2. Drill weight reducing system in front view
Fig 3 Detailed view of weight holding rod with cylinder.
Fig. 4. Schematic layout of the drill weight reducing system in top view.
Fig 5. Ladder and track system
Fig. 6: Model meshed.
Fig. 7: Model with constraints.
Fig. 8: Model with 100N loads on the nodal each point.
Fig. 9. Driving mechanism
Fig 10. Circumferential drilling and ladder stop mechanism.