Exploration Technique: Exploration Drilling
|Exploration Technique Information|
|Exploration Group:||Drilling Techniques|
|Exploration Sub Group:||Exploration Drilling|
|Parent Exploration Technique:||Drilling Techniques|
|Information Provided by Technique|
|Lithology:||Identify lithology and mineralization, provide core samples and rock cuttings|
|Stratigraphic/Structural:||Retrieved samples can be used to identify stratigraphy and structural features such as fracture networks or faults|
|Hydrological:|| -Water samples can be used for geochemical analysis
-Fluid pressures can be used to estimate flow rates
|Thermal:|| -Temperatures can be measured within the hole
-Thermal conductivity measurements can be done on retrieved samples.
Exploration drilling is an important step before development drilling should take place. Exploration drilling is essential for obtaining actual temperature measurements, rock samples, and retrieving fluid samples for chemical analysis. Geophysical methods can give valuable and useful information about the subsurface, which is very important when determining the best locations for drilling; however, in order to obtain actual temperature and fluid measurements, samples need to be obtained via exploratory drilling. There are several different exploratory drilling techniques: core holes, exploratory wells, slim holes, and thermal gradient holes. These exploratory drilling methods are used because they are far less expensive than drilling a full sized production well. Exploratory drilling utilizes drill holes which are normally not as deep, smaller, and quicker to drill compared to production and injection wells. This allows for important subsurface data to be gathered at less cost so better informed decisions can be made about how to proceed in development. Exploration drilling provides the most accurate information during the exploration phase, but it is also the most expensive method, in many cases it is the final phase of exploration.
Exploratory drilling is essential for determining if a geothermal reservoir is capable of producing sufficient hydrothermal fluids for power generation. Exploratory drilling is used for building accurate reservoir models based on hard evidence from what is observed down hole. Exploratory drilling can define reservoir boundaries, estimate production potentials, characterize the subsurface geology, and provide essential fluid geochemical data.
Field procedures vary depending on which type of exploratory drilling is being done. Typically a drill rig for exploratory drilling is much smaller and portable compared to production well drill rigs. The figure below is an example of a drill rig for drilling core holes
Exploratory drilling requires a small amount of land for the drilling area. Roads are usually required in order to transport the drill rig and other equipment to the site. In environmentally sensitive areas such as rain forest or endangered species habitats precautions need to be taken before exploratory drilling can commence because small amounts of deforestation may be required and noise may disturb native species. Exploration drilling may make aquifers more vulnerable to degradation and contamination by connecting aquifers at different elevations and by potentially allowing surface water to enter the aquifers. Suitable precautions will differ from site to site. Wetlands and waterways are also susceptible to exploratory drilling. Unless preventative measures are taken there is potential for contamination from drilling fluids draining into nearby water supplies and entering the environment. An understanding of the hydrogeology of the area is necessary before exploratory drilling should take place.
For all drilling operations careful planning is a critical step before drilling begins. Many factors need to be taken into consideration, such as geographic location, drilling equipment, cost, schedule, well parameters, etc. Drilling near a source of water is often very beneficial otherwise water for the drilling mud has to be transported to the site which can be very expensive. Site accessibility is also very important to take into consideration. Large trucks carrying heavy equipment need to have reasonable access to the site and there needs to be enough space at the site for all the equipment and supplies. Drilling during calm times of the year is very important; climate extremes of hot and cold and high precipitation can affect the mud system, the equipment, and make work condition miserable, ultimately resulting in slower drilling progress and higher expenses.
Exploratory drilling is the most expensive part of exploration and often times it can be difficult to predict the costs due to unexpected problems associated with drilling. Loss of drilling fluid is the most common and expensive problem during exploratory drilling and accounts for over 20% of the costs in exploratory wells. Another pitfall of exploratory drilling is the unpredictability of a well. Some wells can be unstable and collapse or have cementing problems or blowouts which can result in lost effort, time, and money.
- SonicSampDrill. Geotechnical Drilling in New-Zealand [Internet]. 2013. [cited 2013/10/01]. Available from: http://www.sonicsampdrill.com/news/geotechnical-drilling-in-new-zealand.htm
- Government of Western Australia (Department of Mines and Petroleum). 2002. Guidelines for the Protection of Surface and Groundwater Resources During Exploration Drilling. N\A: N/A.
- John Finger,Doug Blankenship (Sandia National Laboratories). 2010. Handbook of Best Practices for Geothermal Drilling. Albuquerque, New Mexico: Sandia National Laboratories. Report No.: SAND2010-6048.
No exploration activities found.