Drilling And Production Techniques In Geothermal Reservoirs

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract The general types of geothermal systems will be defined and the appropriate rock, fluid, pressure and temperature conditions characterizing each type of geothermal reservoir will be identified. These characteristics will be related to the drilling and production problems which are encountered and the present state of the art of pertaining to the solution of these problems. Introduction The population explosion coupled with man's accelerating desire for a higher standard of living has greatly increased his demand for energy in the past, and there is evidence to expect a similar—if nor greater— demand in the future. Quite obviously, natural forms of energy that are readily available at low development cost are those in greatest demand. One of the least expensive energy sources is natural geothermal steam. Although this form of energy has been recognized for centuries, it has been only during the past 20 years that serious efforts have been made to harness it. Natural geothermal steam is now being produced through wells to drive turbines and generate electricity. Identification of geopressured resources has stimulated multiple use development in producing electrical energy, desalinated water, minerals, dissolved gases, etc. The present energy crisis in the U.S. has further accelerated interest in this potential form of energy. Recent development of the Nation's geothermal resources has focused attention on reservoir evaluation and drilling and fluid production problems. It is the purpose of this paper to problems. It is the purpose of this paper to identify these problems and success in their solution, thus far. RESERVOIR CHARACTERISTICS Although geothermal reservoir geology has not been satisfactorily described, it is generally agreed that the geothermal fluid is contained in the porous and permeable matrix rock comprising a structural trap having an impervious cap. The geothermal fluid may exist in the reservoir in the vapor, vaporliquid, or liquid state depending upon the pressure, temperature and fluid composition. pressure, temperature and fluid composition. The matrix rock may be of either the isotropic (intergranular) or fracture type or a combination of the two types.