In 2009, Peppermill Resort Casino expanded its use of geothermal waters by drilling at depth into the Moana geothermal resource. The geothermal resource is of meteoric origin and is assumed to be heated by an intrusive body at depth. Past production of fluids from the resource was limited to shallow, Neogene clastic sediments. The first well drilled into the deeper Kat Peak formation was completed in 1988 and was completed as an injection well. In 2007, with the beginning of a large expansion to the facility, it was decided to make geothermal an integral part of the development plan. Two new deep wells were drilled in 2009 and 2010 to provide additional production and injection capacity. These wells demonstrated a significant improvement in temperature and flow over the earlier shallow wells. The use of acoustic and microresistivity logs, combined with other wireline logs and cuttings analysis, helped to develop a more detailed view of the resource. An intensely fractured zone occurs in the highly permeable andesite from approximately 2,500 ft to 3,400 ft. The majority of fractures in the Kate Peak trend northerly with a dip to the west. This data, with existing structural data, allows hypotheses regarding underlying controls of the Moana geothermal resource, as well as a foundation for further economic evaluation for commercial use.
The PUNA Geothermal Venture wells are located on the Big Island of Hawaii. The project site is close to the Kilauea Volcano with a high geothermal gradient resulting in static bottom hole temperatures above 600˚F. As with most geothermal projects, lost circulation can be a problem in drilling these wells, as it is costly, resulting in drilling delays, hole instability and stuck pipe. These associated drilling problems can ultimately jeopardize the hole. By controlling mud losses, the amount of time combating lost
circulation is reduced, providing a more stable wellbore. Controlling mud losses has also been helpful with logistics since Hawaii is 2,000 miles away from the closest drilling infrastructure. The drilling, as with most geothermal wells, is conducted with unweighted drilling mud containing few solids to bridge the formation and limit fluid losses. To minimize lost circulation when drilling the intermediate hole intervals, micronized cellulose material is introduced into the mud system, which stops lost circulation and/or reduces mud losses to seepage. This ability to control mud losses in the intermediate sections provides improved wellbore conditions for directional drilling and benefits cementing operations. To minimize losses and protect the reservoir, the production interval is drilled with a high-temperature copolymer drilling fluid conditioned with micronized cellulose. The micronized cellulose material being used is a unique fibrous material that has been developed for controlling seepage and lost circulation while drilling depleted, fractured or other permeable zones. This paper will discuss the drilling operation, drilling fluid and the application of micronized cellulose on these geothermal wells.
Increasing power generation at the Soda Lake geothermal power plant requires thorough understanding of the well field and reservoir structure. A three dimensional drill-hole and geologic model was created, incorporating data from temperature surveys, wireline geophysical logs, mudlogs, narratives indicating suspected fault and fracture zones, and numerous technical papers. Once all information was compiled, it was used with other geospatial data to create a drill-hole project in Geosoft’s Target software, with wells oriented in 3D space, and a variety of down-hole data displayed in both 2D and 3D. CSAMT and seismic profiles were dropped into the 3D model, where they could be viewed in conjunction with other data. For the first time, geoscientists could visualize the subsurface locations of all wells with respect to each
other, geology, geophysics, and the temperature anomaly. The result was dozens of data layers that could be toggled on and off and rotated in space. This model was then imported into the Oasis Montaj project, where it was combined with geophysical data to offer a more comprehensive view of the Soda Lake geothermal field. Cross-sections, fence diagrams, and strip logs were easily produced and updated in Target via user-defined templates. Slices of 3D objects such as temperature voxels and geologic surfaces were also displayed in 2D cross sections.
This model has made a valuable contribution to the overall understanding of the Soda Lake geothermal system. As a result, the team has implemented changes leading to increased production at Soda Lake. Two wells that had initially failed as producers were revisited after using the 3D model to study them in the context of their surroundings. One is now hooked into the plant as a producer, while the other is currently undergoing injection testing, with initial tests indicating improvement. An older well was also revisited, and flow tests dramatically demonstrated that a steam cap had developed beneath the well. The 3D model was used in conjunction with geophysical data to study the steam cap, and Magma now has plans for direct use of the steam. In addition, the first of several potential new wells has been targeted and is due to spud in June, 2010.
Drilling and completing geothermal wells in the Salton Sea Geothermal Area represents a unique challenge. Acidic, corrosive produced fluids, combined with high
temperatures and the requirement for a long service life often necessitate high cost, corrosion resistant casing materials. Unfortunately, these materials can be susceptible to wear. Therefore, casing protection becomes vital in providing a long service life. Wear must be minimized, because the resulting damage can be impossible to repair. Rotating drill pipe protectors have been run to protect casing for years, but with shallow casing set points and long bit runs, maintaining protection of the casing results in these protectors being run into open hole. This often causes damage to the protectors, resulting in debris in the hole and subsequent loss of casing protection. On one well in the Salton Sea area, an operator had experienced difficulties in running rotating protectors in open hole. The large volume of debris from damaged rotating
protectors caused a well sidetrack. Non-Rotating Protectors (NRPs) were investigated as an option. As a result, a high-temperature, high-strength version of a Non-Rotating Protector (NRP) that is commonly used in oil and gas cased hole applications, was developed and tested. These tests were run alongside other casing protection methods to evaluate both their durability and their suitability for protecting casing in geothermal wells. In a 2,314 m vertical geothermal well with 1,372 m of 2507 super-duplex stainless steel casing, non-rotating protectors were run immediately above the BHA to evaluate suitability in open hole conditions. They were run 549m into open hole for more than 130 rotating hours at temperatures ranging from 120°C to 190°C. The protectors showed minimal wear and no signs of significant damage. As a result, a program was developed to provide effective casing protection while maintaining an optimized drilling program. The program included the use of computer simulations that predict contact forces and casing wear.
During the 1980s the apparently low permeability 77-29 and 84-33wells at the Soda Lake field were improved into useful long-term production or injection wells with standard perforation recompletions of cemented casings. In the early 1990s long term low pressure injection into well 81-33 either created or restored permeability that had not been recognized or had been damaged during drilling operations. Because of this historic response to stimulation, a technique that employs deflagration
(the targeted ignition of a propellant to force a pressure wave into the surrounding formation) has been performed on 3 Soda Lake wells. In 2009 and 2010 relatively small charges had uncertain success in wells 45A-33 and 41B-33 due to the fact that other well modifications occurred at the same time. Charges 2.3 times larger became available in 2011 and three of these were used in the 25A-33 well. Immediately following the deflagration of the propellant charges, 5 days of low pressure (<150 psi) injection improved the injectivity by 20 fold from 30 gpm to over 600 gpm. Magma ignited the larger charges in three perforated sections of the well at 4153', 4575' and 4911'. Within two weeks of the stimulations using deflagrating materials the injection capacity of the well steadily increased from an initial 30 gpm to a steady flow over 600 gpm, with a maximum of about 750 gpm, all of this occurring at normal injection system pressures less than 150 psig.
Magma Energy (U.S.) Corp. (Magma) acquired a 13 sq mi three-dimensional, three-component reflection seismic survey over the Soda Lake geothermal field in June 2010. The Soda Lake field has been in production since the early 1980’s and gross generation is below name-plate-rating due to declining reservoir temperatures. Magma Energy (U.S.) Corp acquired the plant in October 2008 with the goal of increasing production to the plant’s name plate rating and identify additional resources. To achieve
this goal, Magma made a major effort of integrating existing well field and new geophysical data into a comprehensive 3D GIS interpretation. Integration of the existing well data, 3D seismic and precision gravity led to a new conceptual model and identified two exploration targets outside of the existing producing area that were overlooked for twenty years.
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