WorldWide Drilling Resource

42 AUGUST 2013 WorldWide Drilling Resource ® Drilling Yields Better than Expected Temperatures Adapted from Information from U.S. Geothermal, Inc. U.S. Geothermal Inc. announced its wholly-owned subsidiary, U.S. Geothermal Guatemala, S.A., completed drilling well EC-1 at the El Ceibillo Project located outside Guatemala City. The El Ceibillo geothermal project consists of 9 existing geothermal wells which were drilled in the 1990s at depths ranging from 560-2000 feet; 6 of the wells have reservoir temperatures ranging from 365-400°F (185-204ºC) with highly con- ductive gradients. Fluid samples and min- eralization from the wells indicate the reservoir below the existing well field has high permeability. Recently, well EC-1 was drilled to a total depth of 4829 feet and encoun- tered a bottom-hole temperature of 491°F (255°C). High temperatures in excess of 392°F (>200°C) were encountered begin- ning at a depth of 2625 feet, which rep- resents a potentially high-temperature reservoir interval in excess of 2204 feet. Permeability was encountered, and a slotted liner capable of supporting pro- duction was placed in the well. A prelim- inary cleanout flow from the well was favorable and justifies formal testing. Flow test equipment is currently being fabricated for a planned test, which is expected to be performed this month. Although well EC-1 was originally planned for a depth of 3280 feet, favorable drilling conditions, geology, and increas- ing temperature led the team to extend the well depth. "We are very excited about the pre- liminary results seen from our first pro- duction depth well at our El Ceibillo project in Guatemala", said Doug Glaspey, president and COO of U.S. Geothermal. "Reservoir temperatures within the El Ceibillo area of our concession are sig- nificantly higher than we anticipated, and as a result of favorable drilling conditions, our projected drilling costs for production size wells appear to be at or lower than we have planned." The company is planning to build a geothermal power plant capable of producing 25-50 megawatts of energy. • Simple inst imple installation • Trouble-free operation For more information call: (270) 786-3010 or visit us online: www.geothermalsupply.com Atlantis Vault Studying the Success of Geothermal Drilling Adapted from Information by the International Finance Corporation Before a geothermal power plant can be built, exploration drilling of the poten- tial source must occur. Exploration drilling is one of the largest cost factors, utilizing 35-40% of a project’s capital costs. Improved technologies and tech- niques in geothermal surveying have re- sulted in more accurate targeting, but no one has done an extensive study of the success rates of geothermal drilling. The International Finance Corporation (IFC) developed a global database of over 2600 geothermal wells. This extensive data- base includes information from wells drilled in every decade since 1940, with the oldest well being from 1905. The report, Success of Geothermal Wells: A Global Study , is a report using data from both public and private sources. The report covers several topics such as power capacity, depth, geology type, resource type, well casing size, the suc- cess of the well, and whether a pump is used on the well. Overall success is broken into three phases: exploration, development, and production. For the purpose of this study the first 5 wells were classified as ex- ploration wells, the next 25 were devel- opment, and the remaining wells were classified as operational. The biggest improvements were seen in the exploration phase, making it reasonable to believe surveying and exploration drilling techniques have im- proved greatly in the past few decades. Project developers and drilling compa- nies are becoming more skilled at locat- ing and reaching geothermal sources. The use of directional drilling and other drilling improvements may have also played a role. When the report studied well depth, they discovered well depth did not show any clear trends in influencing either well capacity or success rate. Another interesting determination was regarding the impact that casing size may have on the success rate. Some may assume the larger the diameter of well casing, the greater the flow rate; however, the study indicated there is no obvious relationship between well capac- ity and casing size, but only 441 wells in the study were cased. Additionally, since casing size is determined before the well is drilled and before the characteristics of the reservoir are known, casing sizes may not be optimized tomatch the unique- ness of the resource. Wells with larger casings are more expensive to drill, so it can be tricky balancing drilling costs and the flow rate of the well. Geology seemed to have the highest impact on the success of geothermal wells. The highest average capacities were noted in tertiary and older volcanic systems. Since older rocks are more likely to have large fractures, they have increased permeability, which in turn increases the productivity of wells. Whether you are drilling for water, gas & oil, or geothermal resources, exploration drilling is risky and there is no way to guarantee success, but the payoff can be great! The report is filled with useful data and available online.