Geothermal Drilling - 5 Things You Must Have In Place Before You Break Ground

Transcription

1 Geothermal Drilling - 5 Things You Must Have In Place Before You Break Ground

2 GEOTHERMAL DRILLING - 5 THINGS YOU MUST HAVE IN PLACE BEFORE YOU BREAK GROUND Geothermal drilling is essentially a process wherein a hole is drilled down to the water table so as to use it as a heat source in winter and a heat sink in summer. This heat or thermal differential in the earth can be put to various purposes for example electricity generation is the biggest reason for geothermal drilling on industrial scale. As far as household applications are concerned, geothermal drilling is usually used to improve the efficiency and reduce operational costs of heating and cooling systems of homes, offices and commercial shopping complexes. A refrigerant is pumped down into the drilled hole to extract ground heat in the winter for heating purposes and to transfer heat back into the earth in the summer for cooling purposes. Geothermal heat pump setups can be used in under floor heating systems or connected to the walls of the building. Some systems are designed to operate in only one mode, heating or cooling, depending on the geography and climate of the region. With over one million geothermal heat pumps in operation worldwide providing 12 GW of thermal capacity, it is a booming industry. However, drillers need to be aware of high initial capital costs, tough competition and occupational hazards involved in this business. This white paper discusses five important things you must have in place before you break ground in your next geothermal drilling assignment. 1

3 1. Know How Deep You Need to Drill. It Helps to Get the Right Equipment. Depending on where you are located in the world, the standard depth needed to get the right thermal differential can be anywhere between 50 meters to 300 meters. Drillers who are familiar with the geographic area have an idea of what the standard depth is that they need to drill. If not, you need to do some research or get some geological tests done to have an informed idea of how deep you need to dig. Knowing the right depth allows you to select the right equipment needed to execute the drilling operation be it getting the right rig to do the job and matching the power of the compressor you are going to use. Understand that the depth of the hole to be drilled depends a lot on the footprint available to drill. In compact spaces, the operation may necessitate deeper and more holes in tight confines changing the equipment requirements. Also keep in mind that no two geothermal loop systems are the same. The ground conditions, space constraints, size of the structure and the budget greatly influence the design of the loop system. Small and nimble residential loops, either vertical or horizontal, may be installed with excavators, trenchers, backhoes and sometimes even with horizontal directional drills. However, larger commercial loops, wherein you may be asked to install 50- to 250- meter vertical or diagonal boreholes. So an informed estimation of depth you need to drill lets you select the right rig and pair it with the right tooling. As the depth of the hole increases, the weight of the equipment in the hole increases. The rig you select has to be able to handle the weight of the rods and then retrieve it out of the hole. Studying the literature provided by the rig manufacturers gives the specs on weight handling capacity of your rig and this should help to identify the required rig. Rig capacity, rig footprint, compressor capacity, drill string, fluid cleaning, etc., are some of the factors that you need to keep in mind during rig selection. Understanding the depth requirements of your job helps you select the right compressor that can deliver the required compression of air to finish the job smoothly. As the depth increases, the compressor has to be able to balance the pressure losses at the discharge. This ensures a stable operation under a variety of drilling conditions. Understanding the depth lets you estimate any possible 2

4 requirement of booster compressors and fluid injection pumps to manage the pressure requirements. It is also important to make sure that air hoses being used are in good condition. As they tend to deteriorate with use, they need to be changed with appropriate frequency. Read the manufacturer s specifications charts to understand how often the air hoses need to be changed for the kind of operation you are about to begin. Having a correct idea of depth also lets you identify the correct cuttings handling system. A poor cuttings handling system can clog the hole complicating your job. The hose and the connections from the hole to that hosing need to be maintained in good condition. When you compare the down-the-hole costs of hammers and drill rods with the capital costs you incur on the surface such as labour costs and the cost of diesel you have to burn during the operation, the expenses incurred by drill rods and hammers is quite small as a percentage of the total expenses. So, drillers are better off using good quality equipment than risk the problems of using worn out material in the drilling operations. 2. Check the Wear and Tear Limits of Your Equipment. Understand that the holes that need to be drilled in geothermal heat pumps are relatively deep and the driller has to make sure that the hammer being used is stout and intact. A hammer that broken in the hole, due to wear and tear, may effectively make the hole unusable, wasting precious amounts of time, money and effort. The driller must check the wear limits of the hammer. If it at or close to the wear limits, the driller is better off using a new hammer for a deep borehole job. Hammers that are near their wear limits or just about to touch their wear limits can break off in the hole and you can lose the hole. All service manuals of hammers and other parts come with specifications on wear limits. The driller should check them to see how worn out a hammer is. One way to find wear and tear of a hammer is to use callipers to take the measurements of physical dimensions of the hammer to see if it needs to be changed. If a hammer is worn out internally the pressure it can hold out will be lower than what a new hammer can do. This loss in pressure is noticeable by checking the 3

5 air pressure gauge on the compressor. When the hammer is worn out it will be unable to hold the same pressure as it did when it was new and the driller would typically burn more diesel to compress the air thus incurring more costs. Understand that the performance of the hammer depends on the designed running clearances of its critical components. These should be measured and recorded in your service log. Check the manufacturer s service manuals to find the locations where measurements should be made. Depending on how many parts need to be replaced to bring the hammer back to optimum performance, sometimes it makes sense to replace the hammer altogether to make sure that you go down all the way to the desired depth without breaking your hammer midway through the hole. The next important thing to do is to check the wear limits of bit about to be used in the drilling. A drill bit is what actually cuts the rock. So your DTH hammer is only as good as your drill bit. Abrasive cuttings that pass around the bit at high velocities and the severe stress from the striking piston can strain the down-thehole bits. It is important that you check them thoroughly for wear and tear signs before you begin drilling. Make sure that the bit fits correctly into the hammer and is moving freely within it. You also need to check the carbides. If they are reground then it s fine. If they aren t then they should be reground to attain the desired performance. With use, the size of the bit decreases. If it is too small then it should be discarded and the driller should ideally get a new bit. Just like the hammer, the driller needs to check the wear and tear of the bit. A bit that is too worn or too close to the wear limits may get jammed in the hole, complicating your job. Depending on the ground conditions, drillers may have to withdraw the bit to regrind it half-way through the job. Also check the foot valve in the bit. Make sure that it is tight within the bit. If it is loose then you might have to replace the foot valve. Understanding the depth and other requirements of the job helps you better assess the kind of equipment you need to complete the drilling effortlessly. When selecting the right down-the-hole bit for best possible performance you have to find an optimal balance between penetration capacity and bit life. At times, you might have to sacrifice the bit life expectancy for the penetration speed. The next important equipment to check for wear and tear is drill rods. As in the cases of the hammer and the drill bit, using drill rods that have worn out or close 4

6 to their wear limits may cause you problem half way through the drilling. If they break off in the hole, the driller might potentially lose the hole. So it is important to check the wear limits of the drill rods. Two most frequently used methods are measuring the physical dimensions of the drill rod or to check the weight of the rod. The latter is a more fool-proof method. The service manuals of the manufacturers of the drill rods usually contain the specifications related to wear limits of the rods. Drillers can find the weight of the new drill rod versus the reduced weight at which they must be discarded. Drillers need to consider the tensile and torsional strength of the drill rods to make sure that they can pull the drillstring out of the hole. Since drilling torque is often limited by drill pipe connections, high torque connections should be used in complex drilling operations. Another important thing to check is the threading of the drill rods. If the threads are worn out then the driller may have to replace the drill rods. Depending on the complexity of the drilling job, it might be wiser on the part of the driller to use heat treated tool joints, with superior wear resistance. Last but not least, lubricating your equipment regularly with good quality oil is essential to keep them in good working condition. There are different types of lubricating oils available for drilling equipment. While some countries may have banned the use of mineral oils, you can still get many environmentally friendly oils and greases from suppliers. Also make sure that you have adequate supply of oil in store at the site. 3. Have an Effective Break Out System. During any drilling operation you will have to break out drill rod connections. You will also have to break out the drill bit at the bottom to break lose the chuck to change the drill bit or to regrind it. So it is important that you have to have a break out system that is in optimal working condition. A lot of time is consumed in breaking out the drill rods and bits on the field. Without the right equipment you will incur more loss of time and effort and your job becomes progressively expensive. Some drillers try to engineer out of these problems by taking to hammers. This wastes a lot of time and money in breaking out the products. 5

7 There are many efficient break out systems available in the market. Make sure that your break out system has the capability to handle the diameter of the equipment in use. Break out clamps come in both single and double units. The double unit has the advantage of a second unit that can be fixed on the top of the first set. The upper set of clamps can be rotated in any direction to break lose threaded tool joints. Another advantage is that this system can be used to grip different sizes without having to use slips. 4. Have an Effective Casing System. In most geothermal applications you need to case the borehole to prevent overburden or the loose material at the top of the hole from falling into the hole. In almost all drilling jobs, the driller will have to case all the way to the bedrock. The geology of the soil may further complicate the casing of the borehole. An understanding of the properties of the soil will help you come up with the best casing methods and solutions before drilling is commenced. Regulations require you to seal off the aquifer to prevent contamination by wellbore and drilling fluids. This necessitates proper casing. Casings are also important to isolate unstable formations such as swelling, sloughing and unconsolidated formations. Geological zones with high or untreatable lost circulation and depleted pressure zones above the production horizon also demand proper casing. The driller should have correct information about borehole profile so that a casing of correct diameter, weight and grade is selected. Casing has to withstand different kinds of loading in different situations, and the most common design criteria are for burst pressure, collapse pressure, and axial tension. Burst pressure and axial tensile strength for a given casing size are a function of the casing grade, but collapse is more related to the wall thickness, because collapse is determined by the material s elastic properties and geometry, as well as its tensile strength. There are many ways to case a geothermal borehole but two methods are particularly popular casing the hole almost immediately after the hole is dug and casing as you drill. The prevalence of these methods depends a lot on the country, geology and the job requirements. 6

8 Casing-while-drilling eliminates costs, time, and problems related to tripping drill pipe. Time to trip drill pipe and handle the Bottom Hole Assembly (BHA) is a significant fraction of total time and cost on some wells, but it is also the case that many problems of well control and hole stability are associated with trips. Casing-while-drilling can help you reduce lost circulation problems. Such systems can continue drilling when lost circulation is encountered. The rock cuttings tend to be washed into the fractures or permeable zones, acting effectively as lost circulation material. The relatively narrow annulus also means that fluid flow rates can be lower than would be used with conventional drilling in the same size hole. The ability to drill through lost circulation zones, or other weak formations, means that sometimes the casing can reach a greater depth than would be the case with conventional drilling. While casing-while-drilling is the most efficient one, no matter what type of casing system you choose it is important that you case the hole well and pump enough cement into the annulus that fluids in different zones are effectively prevented from getting mixed up. Only a good casing system that is in optimal working condition can ensure this. It is vital to cement all of the annular space behind the casing. Cement prevents the casing from expanding or collapsing when heated and helps prevent corrosion. Also make sure that you have all the casing necessary to go all the way down to the hole. Depending on the depth of the hole, you need to ready as many meters of steel casing on the site to finish the casing as fast as possible. If the complexity of the drilling demands it, then you may choose to opt for a rig that has a dual rotary head for rotation of the casing as well as the drill which considerably increases the precision and drilling efficiency. 5. Safety Should Be Your First Priority. Geothermal drilling rigs are heavy equipment and their use involves working with high pressure air and powerful mechanical devices. This profession comes with certain occupational hazards and if proper safety precautions are not taken then drillers expose themselves to an increased possibility of risk and danger. 7

9 Safety of your workers is very important and make sure that you understand, implement and follow the safety precautions specified by your statutory authority for drilling operations. Your drilling crew must be provided with special clothing and protective equipment such as hard hats, goggles, gloves, aprons, wet gear, earplugs or muffs, dust masks, etc. You should fence off the area to prevent unauthorized people from entering the drilling area. But some complex geothermal drilling operations do produce water at temperatures above F. If temperatures near or above this are anticipated, then appropriate equipment such as rotating head, banjo box, blooie line, safety apparel, fencing, etc., must be used. A blowout may cause considerable harm to the people in the vicinity. In such circumstances, the drilling crew must be provided with safety equipment. The operator must address all safety considerations arising from such situations. Research shows that drill pipe handling is the most frequent cause of accidents in geothermal drilling. Before commencing the work, the entire crew should be instructed and trained in well control and in the correct and safe use of all equipment and machinery with which they work, and a logbook shall be maintained to record such instruction and training. At least one trained person who has attended a recognized first aid course and holds a current certificate of competency in first aid should be available on site at all times during drilling operations. Your crew must be made aware of the hazards normally associated with drilling together with the hazards associated with hot geothermal fluids. It should include testing for carbon dioxide and hydrogen sulphide, well quenching, spontaneous well discharge, hot water blowouts and other site-specific hazards. It is always useful to have gas detectors and breathing escape apparatus on site if any such hazardous gases are expected. Conclusion We hope this short whitepaper has given you some useful information of things to consider ahead of your next Geothermal drilling project. Typically a bit of time spent upfront in planning your projects can make things run smoother when on site. 8

10 About Mincon International Mincon International was established in Shannon, Ireland in 1977 and has grown into a global business with a presence across 6 continents. Mincon produce a range of high quality DTH hammers and bits for a wide variety of drilling applications. With three state of the art manufacturing facilities in Shannon, Ireland, Benton, Illinois, USA and Perth, Australia, Mincon can supply its products worldwide. If you need specific advice on your next drilling project or would like to arrange a site trial with our hammers and bits then get in touch with your local office today: 9