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The drilling conditions described above have led to the following practices, which are reasonably uniform, in the geothermal drilling industry. Bits Because of the hard, fractured formations, roller-cone bits with tungsten-carbide inserts are almost universally used for geothermal drilling. The abrasive rocks mean that bit life is usually low (50 to 100 m), but many bits are also pulled because of bearing failures caused by rough drilling and high temperature. Polycrystalline diamond compact (PDC) bits have the dual advantages of more efficient rock cutting and no moving parts, but experience with PDC bits in geothermal drilling is both scant and unfavorable. Much research and development in hard-rock PDC bits is under way,  so it is possible that these bits will come into wider use in geothermal drilling.
Although drilling for geothermal energy is quite similar to drilling for oil and gas, there are some aspects of it that are unique. The high temperatures associated with geothermal wells affect the circulating system and the cementing procedures as well as the design of the casing and drilling string. The unique problems must be coped with along with those normally encountered. Introduction Geothermal energy is simply the energy derived from the earth's magmatic heat. This would include all the products of geothermal processes, naturally occurring products of geothermal processes, naturally occurring and artificially induced. Steam, hot water, and minerals are some of the most important direct products of geothermal resources.Geothermal power was recognized first in Italy in 1904 as a future source of energy. It was not until the mid-1950's that the U. S. became seriously interested in geothermal power, the chief reason being that until this time other energy sources were plentiful.In 1955, a drilling program began in the Geysers area of California. The first geothermal power generator in the U. S. began operation in the Geysers in 1960. Since that time the drilling activity hasincreased substantially and several generating plants have been constructed, The total capacity of the Geysers is presently in excess of 300 megawatts (Mw), which ranks the U. S. as the second leading nation in geothermal power production. This activity stimulated the exploration for geothermal resources in other areas of the country, especially in other parts of California.The Imperial Valley of California is another center of geothermal interest. Unlike the Geysers area, which produces dry superheated steam, the Imperial Valley produces hot brine. There are presently several wells being drilled in the latter area and there have been many proposals to utilize the available geothermal power. The Imperial Valley Geology The Imperial Valley is essentially a flat, featureless, alluvium-filled basin trending northwestward from the Gulf of California to and including the Coachella Valley. The sediments filling the Imperial depression are primarily sandstones, shales, claystone, and conglomerates deposited by the ancestral Colorado River as it formed its delta. The sediments range in thickness from 8,000 ft in the northeastern Coachella Valley to 17,000 ft in the southwestern Imperial Valley.Three major fault systems, all with northwesterly trends, are present in the Imperial Valley. The San Andreas zone travels along the northeast side of Coachella Valley. The San Jacinto and Elsinor fault zones are on the northwest side of the Imperial Valley. Most of the numerous faults in the three systems have right lateral and vertical movement, with the northeast block structurally higher than the south-west block. Surface Locations Most locations for drilling operations pose no real problem since the terrain is nearly flat. The primary problem since the terrain is nearly flat. The primary surface problem in the Imperial Valley is the extreme heat to which the personnel and the machinery are exposed. Water for the drilling operations is usually obtained from one of the many irrigation canals that cross the Valley or from water wells. JPT P. 1033
Typical geothermal wells produce low pressure steam or hot brine from relatively shallow depths. However, effects of 350-700 degrees F temperatures and 100% aqueous environments create completion and operating problems that are foreign to even experienced oil d gas well operators. Unusual problems with casing that is otherwise properly designed for basic tension, burst and collapse properly designed for basic tension, burst and collapse are presented. Serious results of primary cementing limitations caused by severe hole conditions are emphasized. And state of the art completion methods and special problems in three major geothermal development areas are reviewed.
In several areas in the Western United States, geothermal resources have been favorably assessed and wells are now being drilled and completed with the potential to supply power to electric generators, when potential to supply power to electric generators, when such plants are installed. Such wells typically will flow large volumes of superheated brines from which commercial quality steam will be separated. A viable operation is already supplying electricity in a nearby development in Cerro Prieto, Mexico. And dry steam wells are being produced commercially from non-typical, geothermal reservoirs in The Geysers area of northern California. These developments represent a variety of downhole conditions and reservoir characteristics ranging from those in highly underpressured, air drilled, fractured volcanics to conventional-appearing sediments with unique problems caused by high volume, hot water flows.
This paper is an overview of state of the art technology, recognized problems and limitations relevant to completion and production of geothermal wells. Technical discussion will include:
1. Casing failure modes - -design considerations, and effects of unique hole conditions and geothermal fluid environments.
2. Completion methods - - operations and problems in Western U.S. and Cerro Prieto (Mexico) fields, and productivity/injectivity considerations.
Studies were conducted under contracts with Sandia Laboratories of Albuquerque as part of a federally funded program designed to promote industry development by significantly reducing the cost of drilling and completing geothermal wells. Two important objectives are early definition of practical problems and rapid technology transfer. Some aspects of the technology will apply to geopressured geothermal wells planned for Texas and Louisiana. And Los Alamos Scientific Laboratory's Hot Dry Rock Development Program in New Mexico, sponsored by DOE, is an experimental geothermal operation with related technology needs.
CASING DESIGN CONSIDERATIONS
Geothermal wells are relatively shallow, typically 5,000-9,000 feet. Reservoirs are normally underpressured relative to a full column of fresh water. And wells are produced at maximum attainable rates through open casing strings to minimize friction loss. Factors that limit casing diameter are cost, drilling and cementing problems in large diameter holes, and collapse rating limitations. The entire well/gathering system should be optimized as friction loss in flowlines must be considered. In dry steam wells, too-large casing may reduce flow velocity and cause downhole condensation.
Proper injection well design will be equally important. Reinjection of cool brines to the producing zone will be required in certain large-scale geothermal projects in sedimentary basins. Injection wells will projects in sedimentary basins. Injection wells will have large diameter tubing, and completion programs will consider reservoir injectivity, per well pressure/ rate requirements a spacing. Presently, plant condensate is injected as a disposal requirement at The Geysers and reinjectivity is being evaluated in the Imperial Valley. However, in Cerro Prieto, separated water and plant condensate flow to a large surface lake in uncultivated desert.
An example geothermal well completion is illustrated in Fig. 1.
Abstract: With the concern over anthropogenic climate change (i.e. man-made climate change), there is a growing awareness that we must utilize energy resources that are sustainable. The power obtained from geothermal reservoir is one such sustainable resource that has the potential to supplement our energy systems and to displace many conventional fuels. In contrast to many renewable technologies, such as wind or solar, the geothermal resource can be used 24 hours a day, 7 days a week without any harm to the environment. It is due to this reason that geothermal development, a natural extension of oil and gas development activities, is attracting both new petroleum engineering graduates and established petroleum engineers in increasing numbers. Along with the importance of geothermal energy, this paper details as to how different phases of geothermal industry like drilling, production, and reservoir utilize petroleum engineering techniques, the challenge awaiting engineers as they work to solve first- time problems and improve technology for future activities. The geothermal industry has tremendous potential for growth and will make a significant contribution to worldwide energy supplies. Introduction: The basic study from which this paper is prepared is the result of rapidly depleting petroleum reserves and the growing need throughout the world for increasing quantities of energy in all forms. Quite obviously, natural forms of energy that are readily available at low development cost are those in greatest demand. The underdeveloped countries and particularly those having little or no petroleum resources, are the countries in which the most interest is being shown in the newer energy sources. One of the least expensive energy sources is natural geothermal energy. Although this form of energy has been recognized for centuries, it has been only during the past few decades that serious efforts have been made to harness it. Geothermal energy is heat energy originating deep in the earth's molten interior. It is this heat energy that is responsible for tectonic plates, volcanoes and earthquakes. The origin of this heat is from primordial heat (heat generated during the Earth's formation) and heat generated from the decay of radioactive isotopes. The temperature in the earth's interior is as high as 7000°C, decreasing to 650 - 1200°C at depths of 80 km -100 km. Through the deep circulation of groundwater and the intrusion of molten magma into the earth's crust, to depths of only 1 km-5 km, heat is brought closer to the earth's surface. The hot molten rock heats the surrounding groundwater, which is forced to the surface in certain areas in the form of hot steam or water (e.g. hot springs and geysers). The heat energy close to, or at the earth's surface can be utilised as a source of energy, namely geothermal energy. The total geothermal resource is vast. However, geothermal energy can only be utilised in regions where it is suitably concentrated. These regions correspond to areas of earthquake and volcanic activity, which occur at the junctions of the tectonic plates that make up the earth's crust. It is at these junctions that heat energy is conducted most rapidly from the earth's interior to the surface, often manifesting itself as hot springs or geysers. There is currently an estimated 15,000 MW of direct use and over 9,000 MW of generating capacity in geothermal resources worldwide. To put geothermal generation into perspective, this generating capacity is about 0.4% of the world total installed generating capacity.
van Oort, Eric (The University of Texas at Austin) | Chen, Dongmei (The University of Texas at Austin) | Ashok, Pradeepkumar (The University of Texas at Austin) | Fallah, Amirhossein (The University of Texas at Austin)
Abstract Deep closed-loop geothermal systems (DCLGS) are introduced as an alternative to traditional enhanced geothermal systems (EGS) for green energy production that is globally scalable and dispatchable. Recent modeling work shows that DCLGS can generate an amount of power that is similar to EGS, while overcoming many of the downsides of EGS (such as induced seismicity, emissions to air, mineral scaling etc.). DCLGS wells can be constructed by leveraging and extending oil & gas extended reach drilling (ERD) and high-pressure high-temperature (HPHT) drilling expertise in particular. The objectives of this paper are two-fold. First, we demonstrate that DCLGS wells can generate power/electricity on a scale that is comparable to EGS, i.e. on the order of 40-55 MW per well. To this extent, we have developed a coupled hydraulic-thermal model, validated using oil and gas well cases, that can simulate various DCLGS well configurations. Secondly, we highlight the technology gaps and needs that still exist for economically drilling DCLGS wells, showing that it is possible to extend oil & gas technology, expertise and experience in ERD and HPHT drilling to construct complex DCLGS wells. Our coupled hydraulic-thermal sensitivity analyses show that there are key well drilling and design parameters that will ultimately affect DCLGS operating efficiency, including strategic deployment of managed pressure drilling / operation (MPD/MPO) technology, the use of vacuum-insulated tubing (VIT), and the selection of the completion in the high-temperature rock zones. Results show that optimum design and execution can boost geothermal power generation to 50 MW and beyond. In addition, historical ERD and HPHT well experience is reviewed to establish the current state-of-the-art in complex well construction and highlight what specific technology developments require attention and investment to make DCLGS a reality in the near-future (with a time horizon of ~10 years). A main conclusion is that DCLGS is a realistic and viable alternative to EGS, with effective mitigation of many of the (potentially show-stopping) downsides of EGS. Oil and gas companies are currently highly interested in green, sustainable energy to meet their environmental goals. DCLGS well construction allows them to actively develop a sustainable energy field in which they already have extensive domain expertise. DCLGS offers oil and gas companies a new direction for profitable business development while meeting environmental goals, and at the same time enables workforce retention, retraining and re-deployment using the highly transferable skills of oil and gas workers.