Drilling a new well can often be one of the biggest investments that people make in a year. Whether it be a new expansion, or replacement of an old, defunct well, drilling projects are involved and complex, so it should never be approached without gathering all the data possible. There are several ways to acquire information about a particular site, which will help determine what the new well should look like, but none as powerful as drilling a test hole.
A test hole is a small diameter borehole which is drilled at, or right next to the new proposed well, which gives the most accurate representative information of what is going on below ground at that site. There are primarily 3 key pieces of information that the test hole provides:
- Water existence - Probably the most important piece of information you can get about a site is whether there is any water at all at the given location. While this may not be an issue in areas with know water, it consistently is a concern in more arid regions, such as areas in Nevada where there may not be any subsurface water at all. Additionally, during drilling you can get a better idea of just how far down that water can be. It's not uncommon for test holes to go 100-300 ft deeper than the design depth of the production well, just to better understand what might be available.
- Lithology - This is the geological makeup of the soils that are being drilling through. During the test hole, Drillers screen and collect samples which are representative of the layer being drilled into. Often these samples are taken every 10 ft, but can be more often or less based on changing conditions. This testing and sampling helps determine if the well will be in hard rock formations, loose sands/gravels, volcanics, boulders, clays, or any number of possible soil profiles throughout the test hole depth. The lithology helps aid in well design and sheds light on areas while have the higher potential for water.
- ELog & Laterolog - This final step of the test hole drilling involves lowering specialized tooling into the borehole, which measures resistivity throughout the well depth. The data collected from these tools helps paint the picture to where high water bearing zones exist or alternatively, areas with minimal potential. Typically , results of the ELog help define where screen sections should be placed to maximize well performance.
While there is no magic bullet to say exactly how much water a zone can produce, knowing where the zones are, the lithology of those zones, and activity on the Elog at those zones, gives the best data possible to make decisions about the final well design. Sometimes, results of the test hole can be dismal and lead to selecting a new well location, rather than making a large investment into an underperforming well. The cost of the test hole is fractional, compared the cost of the new well, so getting the best, most representative data possible, prior to drilling the new well, is a no-brainer.
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