Application of power hammer technology in water well drilling

The precise definition of drilling application comes from selecting the best drilling method and accurately evaluating the feasibility of drilling with high-pressure compressed air and DTH hammer. Figure 1 is the flow chart of drilling method and rig selection. The whole process includes continuously collecting and interpreting data, and finally describing the working environment, drilling design, drilling process and equipment requirements in detail. Figure 2 is the data collection table used by Ingersoll Rand Company to select drilling scheme and drilling rig.

Figure 1 Drilling Method and Drilling Rig Selection Flowchart

Figure 2 Drilling Data Collection Table

2 Geological evaluation

The first step in the evaluation process is to collect underground geological and hydrological information. In many cases, this information can be obtained from previous drilling records or directly from actual drilling operations in this area. In addition, we can also get some relevant information from some government agencies (such as geological prospecting bureau, oil and gas association) or universities. Figure 3 is a drilling design information collection table, which we will discuss as an example throughout the article.

Figure 3 Drilling Design Information Collection Table

The geological profile shows that shale, limestone and sandstone are under the topsoil and loose shale. Previous drilling data in this area showed the following perforation velocities in different formations:

New technology of water well drilling and completion

This means that air DTH hammer drilling can achieve excellent work efficiency and should be the first choice for drilling in this terrain when geological conditions permit and drilling design parameters meet. Figure 4 shows the relationship between formation and drilling method.

3 Hydrological assessment

Hydrography also plays an important role in evaluating the feasibility of using air DTH hammer and whether the expected perforation speed can be achieved. Where there is water and the amount of water during drilling are directly related to the pressure and volume of compressed air needed for drilling and hole cleaning. If a large amount of water rushes into the hole during drilling, the working efficiency of DTH hammer will be reduced, or in extreme cases, DTH hammer will stop working until the water quantity is controlled. In our example well, the amount of water entering the surface borehole is 189 liters/minute.

Fig. 4 Relationship between strata and drilling methods

The methods to control water inrush include: increasing the volume and pressure of compressed air; Spray a small amount of water and additives (such as foaming agent or polymer) into compressed air; Connect special gas-lift joints between drill pipes to control gas volume and water volume. In our example well, after using foam additives and gas lift connection, the water quantity in air DTH hammer drilling is effectively controlled.

Generally speaking, we can obtain written information about hydrogeology and previous drilling plans from relevant local institutions or water well contractors. Hydrogeological research is very important for effective planning and implementation of drilling projects.

Figure 3 shows that the amount of groundwater is extremely low, and it is only limited to the surface and underground area of 300m m m. During drilling, the inflow of water can be easily controlled without adding compressed air or using any additives.

4 Drilling design

The opening and the surface casing are lowered to a depth below the water gushing area. The surface casing is cemented to the surface from the bottom of the open hole to block surface water and prevent groundwater from entering the hole. After drilling, install a flange on the top of the surface casing, and then install an exhaust protection rotary head on it to control the scattering pollution during drilling.

The well design (casing specification) determines the diameter and depth of the borehole. The selected drilling method must ensure a clean straight hole, and the hole diameter must be large enough to facilitate casing running. The required aperture and depth are not only important factors for selecting the best drilling method, but also directly related to the geological and hydrological characteristics of the formation. In drilling applications, the air DTH hammer is most effective for drilling holes with a diameter of 6 "(152 mm) to (3 1 1 m m) in moderate to extremely hard formations with moderate or low water inflow.

5 Drilling tool design

Drilling specifications and drilling methods determine the design of drilling tools. The purpose of selecting drilling tools is to ensure that they have enough strength to overcome the compression, tension and torsion loads during drilling. All components of drilling tools must have a hollow space to effectively contain drilling fluid and slag discharge.

All components must be able to be accommodated by the oil well and have enough weight to achieve the best perforation speed. The design of the drilling tool determines the performance of the main components of the drilling rig, such as feed (lifting), rotation and circulation loop.

Unlike roller drilling, DTH hammer drilling does not need to rely on the weight acting on the bit to drill holes. The whole drilling is realized by a series of rapid and high-intensity blows to the bit surface and the slow rotation of the ball teeth. Because of this, the drilling tools of DTH hammer do not need to be very heavy, and large parts such as drill collars can also be drilled quickly. Lighter drilling tool components mean easier and safer operation, and give the drilling rig deeper drilling capacity than air roller or mud drilling. If the casing weight exceeds the drilling tool, the heavier casing must be matched when selecting the drilling tool capacity. In our example well, the weight of drilling tool exceeds the weight of casing, so we use the weight of drilling tool to determine the lifting force of drilling tool.

6 drilling rig capacity

6. 1 feed

Once the size and weight of the drilling tool and casing are selected, the final capacity of the drilling rig can be determined. We usually add a safety factor of 25% to the total weight of drilling tools to determine the lifting force of drilling rigs.

Modern hydraulic top-driven rotary drilling rig acts on the wire rope connected to the rotary head through the hydraulic cylinder, providing lifting and feeding force for the drilling tool. This system can quickly lift and feed, and at the same time it can be accurately controlled.

The drilling rig also has a drilling feed system which can accurately control the weight acting on the drill bit or DTH hammer. In addition to pressurizing or lifting the drilling tool, the drilling feed system can accurately control the force acting on the drill bit or DTH hammer even when the weight of the drilling tool exceeds the weight required by the drill bit. The operator sets the system to offset part of the weight of drilling tools by lifting, so as to accurately control the weight acting on the drill bit and ensure the best drilling efficiency.

Roller drilling relies on rotation and great weight acting on the drill bit to drill holes. In hard rock area, a (3 1 1mm) roller bit needs a mass of 23000~27000kg to achieve the best perforating speed. In order to meet the optimum weight acting on (3 1 1 m m) roller bit, a 6 "(152 mm) drill collar with a length of 260 m is needed. For a hole with a depth of 1372 m, this means that the drilling efficiency is about 20% lower than the standard.

Because DTH hammer uses the energy generated by compressed air itself, there is no need for drilling tool parts as heavy as roller drilling. DTH hammer drilling tool is lighter and cheaper, and it is easier and safer to operate during drilling. A (3 1 1mm) DTH hammer bit only needs 3000~3600kg to meet the requirements of rapid drilling. DTH hammer can reach the fastest opening speed. When drilling, modern hydraulic top-drive rotary drilling rig accurately controls the weight acting on DTH hammer through pressurization. With the increase of hole depth, more and more drilling tools are put into use. At this time, the operator can ensure the best weight acting on the drill bit and obtain the maximum drilling efficiency by continuously reducing the pressure and finally lifting until the hole is formed. The drilling rig using winch, even if equipped with automatic drilling system, can not control the weight acting on the bit, so it can not achieve the best effect.

6.2 rotation

Well design and drilling method also determine the ability of rotating head. Drill a hole of 6 inches (152mm) to (3 1 1 mm) with an air DTH hammer, with a torque of 82110848n m and a rotating speed of 20 ~ 60r/min. Hydraulic rotary drilling rig has the advantages of high torque output and stepless speed regulation at any speed.

Roller bits drill holes by rotation and the weight acting on the bit. In many strata, the geological structure characteristics easily lead to the deviation of roller bit from the vertical borehole direction. In order to avoid this phenomenon, it is necessary to use special drilling tools at the bottom of the hole to force the roller bit back to the correct track. However, these drilling tools are heavy and expensive, and they require larger rigs with greater lifting force and torque to ensure drilling to a set depth. In many cases, because the casing cannot be lowered to the required depth, the inclined borehole must be re-drilled or abandoned.

Because DTH hammer uses vertical force drilling, the tendency of well deviation is much smaller. In the stratum prone to well deviation, a short centralizer can be added above DTH hammer to control well deviation.

6.3 cycle

Compared with other drilling rig components, the capacity of air compression system (air compressor) has the greatest influence on drilling cost and efficiency. The displacement of the air compressor [cubic feet per minute (ft3/min), or cubic meters per minute (m3/min)] is used to impact the DTH hammer, clean the bit surface and discharge slag. The pressure of air compressor [pound per square inch (1b/in2) or kilogram force per square centimeter (kgf/cm2)] is used to provide the impact energy of DTH hammer, discharge slag and overcome the water pressure in the hole.

Figure 5 shows the air volume and air pressure required to ensure the normal operation of DTH hammer, which can drill holes from 6 inches to 24 inches.

Fig. 5 Gas and air pressure required by Ingersoll Rand DTH hammer

In practical application, if more water flows into the hole, supercharger can be used to ensure the pressure difference between DTH hammer and drainage slag discharge. Figure 6 shows the influence of water level during drilling.

Fig. 6 Influence of water level on air pressure

At present, top-drive rotary drilling rigs often use two-stage high-pressure screw compressors to provide circulating air. These air compressors, such as Ingersoll Rand HR-2.5, have a rated displacement of 34.5m3/min and a rated pressure of 24. 1(kgf/cm2). They can be directly installed on the drilling rig (such as RD20), or they can be provided separately as fixed or mobile (Figure 7). These air compressors are specially designed for oil field service, and are applied to water well drilling, with excellent efficiency and high reliability record.

Figure 7 Deck design of RD20

In some cases, when the pore size is large, the formation is unstable or there is a lot of water gushing in the hole, water, foaming agent and polymer can be sprayed into the drilling air through the hydraulic drive water spraying system on the drilling rig. These additives expand the performance of air DTH hammer, and their functions are as follows:

(1) Increase the viscosity of compressed air and improve its ability to effectively lift and carry cuttings at low speed.

(2) Increase the bubbles of water gushing in the hole, reduce the density of water and facilitate slag discharge.

(3) Adding colloid of compressed air can form a protective layer on the surface of the hole wall, reduce the inflow of water and stabilize the hole wall.

These water jet pumps are hydraulically driven and variably controlled pumps with appropriate pressure to overcome air pressure.

DTH hammer needs internal lubrication when working. The drilling rig is equipped with DTH hammer lubricator. When DTH hammer works, a small amount of lubricating oil is injected into compressed air. The fuel injection quantity of the system is adjustable, and there is suitable pressure to overcome the drilling air pressure.

6.4 Actual drilling efficiency

Fig. 8 is a schematic diagram of an actual production well in the eastern United States. The geological and hydrological environment determines that the well is designed as a multi-stage borehole and casing. This well was drilled with DTH hammer by Ingersoll Rand -20 drilling rig. The whole drilling process is in two shifts, and three people in each shift work continuously at 12h. The size of the drill pipe is × 30ft (114mm× 9.1m), with a flat shape and a weight of 25.6kg/m. The maximum total weight of the drilling tool is 19332kg. The maximum lifting force of RD-20 is 54432kg. The pilot hole with a depth of 6m is drilled with air cone foam. At the upper part of the borehole 22 1 m, the formation water yield is about 189 L/min. Ingersoll Rand DTH hammer is used to drill from the bottom of the pilot hole to a depth of 674 m. Because water flows in between the surface layer and the hole, foaming agent is injected to reduce the upward speed and help drainage and slag discharge. Add a one-way joint (gas lift) to control the water quantity every152m drilling tool.

Fig. 8 an example of a gas well in a coal seam in the eastern United States

Figure 9 shows the drilling progress during the whole completion process. Average completion speed of the whole well 12m/h, average penetration rate 38m/h, average casing running speed 168m/h, average casing running speed 259m/h. The average speed of connecting rod and unloading rod is 305m/h, and the whole completion time is 78h, including preparation and evacuation time.

Figure 9 Actual drilling progress of coalbed methane well