PACIFIC OCEAN Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 150 ABSTRACT DEVELOPMENT OF XRD IN EL SALVADOR Elizabeth de Henríquez LaGeo S.A. de C.V. XRD has played an important role in identifying mineralogical compositions of well samples and corrosion and scaling products of surface equipment in the geothermal fields in El Salvador. Results have complemented the petrographic analysis and geochemical studies, and have provided a wider understanding of the geological, petrological, geochemical, and thermodynamic processes. Interpretations of permeability and temperature have given a broader outlook of the geothermal system. XRD technique was not limited to the geothermal industry. Samples from different industries are being accepted, such as solid particles in air and water for environmental purposes, cement industry, construction, mining and metallurgy, paint industry, refineries, and universities. INTRODUCTION El Salvador is a small country in the heart of Central America bounded by numerous volcanoes, which makes geothermal energy viable to the country (Figure 1). LaGeo took the lead in exploring and developing the geothermal energy resources to address the growing energy needs of the country. The electricity growth went hand in hand with the country s economic development. G U A T E M A L A LEMPA RIVER H O N D U R A S SAN SALVADOR Figure 1. Location map of Ahuachapán and Berlín Geothermal Fields.
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Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 151 At present, LaGeo has two developing fields in El Salvador: Ahuachapán geothermal field in the western part of the country, and Berlín geothermal field in the eastern part, contributing 22% of the total electrical generation of the country. Geothermal energy exploration in El Salvador started in the 1970s where scientific investigations have increased and have aided in the understanding of the geothermal system, which finally brought the creation of the laboratory of chemistry and geology. The laboratory of Geology in LaGeo is responsible in interpreting, analysing, and evaluating the physical, mineralogical, and thermodynamic characteristics of the lithological formations, and all solid deposits encountered during the exploration and development of geothermal areas. It is divided into two parts: Petrology and X-ray Diffraction (XRD). HISTORY OF XRD The XRD technique has been part of the company since the 1970s when the first XRD machine brand Philips PW-1730 was acquired by CEL (former owner of the company) on January 15, 1979 to provide a more complete mineralogical analysis mainly on rock samples. Geologist Aida de Zamora was assigned to handle the machine, complemented by her training in USGS laboratory in Menlo Park, California. From 1978-1983, the XRD analysis provided the mineralogical data of all wells in the Ahuachapán geothermal field, establishing correlations of the fluid distribution and temperature of the field. However, at the end of 1983, the machine suffered electronic damage because of voltage fluctuation in the national electricity grid. This brought a great effect in the electrical generation program of CEL, which required investigations and geoscientific studies to guarantee the adequate operation and optimisation of each project. This included drilling of more wells, and in particular the study of alteration mineralogy. In 1986, the machine was repaired, but however several defects were identified that took the machine out of service in 1995. Under the recommendation of the IDB (Interamerican Development Bank) consultants, the new XRD machine Siemens D5000 (Figure 3) was acquired in 1996 to continue with the development of the Berlín geothermal field. Another geologist, Luz Antonina Barrios, was designated to coordinate the laboratory from 1996 to 1999. 1999 was a turning point for the company as the restructuring gave way for the laboratory to open its doors, not only to geothermal application, but also to industrial uses. The acquisition of the new XRD machine enabled the processing of larger amounts of samples daily, due to the numerous sample holders that the equipment possesses. With the help of the software EVA, mineral identification of samples became faster and more reliable as thousands of minerals are available in the database.
Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 152 The use of chiller as the cooling system allowed the machine to run samples for 12 hours a day without interruption. In 1998, the old XRD machine was donated to the University of El Salvador making it at present the company s competition for the market. ROLE OF XRD IN THE EXPLORATION AND DEVELOPMENT OF GEOTHERMAL FIELDS XRD has played an important role in identifying mineralogical compositions of altered zones in volcanic areas, rock cuttings during drilling of wells, corrosion, and scaling deposits in surface equipment and in wells. Figure 2. Clay minerals in rock samples. Figure 3. Fumarole in Cuyanausul. A. Altered rock samples: (See Figure 2). Most clay minerals and other alteration minerals are identified by XRD, which helps delineate zones of interest, structural features, and physical changes in the rocks (permeability, porosity, density, etc.). B. Samples in Fumaroles The study of alteration minerals in fumaroles helps identify the alteration minerals (Figure 3) and alteration assemblages, its relation with the deep hydrothermal fluids, geologic structures which indicates permeability in the area, and thermal history of an area. Similarly, it provides information which can be correlated with geochemistry of gases, geothermometers and geochemical evolution of wells, etc. C. Samples in Wells (both cuttings and core samples ) Identification of hydrothermal alteration minerals and clay minerals in well samples is important during drilling. It can define drilling problems such as stuck pipe caused by swelling clays. It can characterize alteration types or mineralogical facies (Figure 4). It can predict temperature of formation and the rate of alteration processes. It can indicate fluid chemistry and source of fluids and permeability and thermal history of a system.
Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 153 Alteración Total vs Profundidad Pozo TR-10A 100 90 Alteración Total Epidota Calcita Wairakita 80 70 60 Alteración ( % ) 50 40 30 20 10 0 1440 1470 1500 1530 1560 1590 1620 1650 1680 1710 1740 1770 1800 1830 1860 1890 1920 1940 1960 1990 2010 2040 2070 2100 2130 2160 2180 2210 2240 2270 2300 Profundidad ( metros ) Figure 4. Alteration minerals vs depth. Figure 5. XRD Graph of a sample in drainpots. D. Samples in surface equipment (both corrosion and scaling) After drilling, well scales, corrosion products, and well ejecta are being analysed to determine the chemical composition and temperature of the fluids within the well as well as determining flow regimes and corrosion (Figure 5) along the length of the pipelines and other surface equipment such as valves, cyclone separator, etc. Scales and corrosion products identified in XRD have enabled the degree of corrosion in turbine blades and have determined the steam purity entering the turbine. By means of the mineralogical compositions of corrosion and scaling deposits, it can define possible changes in the materials of surface equipment for more durability. Likewise, additional equipment in the pipelines can be recommended to eliminate solid particles and avoid damage in the installations of geothermal plant. PRESENT STATUS An analysis of the number of samples was undertaken to show the trend of the origin of the samples. From the graph in Figure 6, the samples analysed were mostly from the Berlín geothermal field (BGF), as its development started at the same time with the acquisition of the new XRD machine. Monitoring of the geothermal field (corrosion, scaling and fumaroles) was more regular and periodic. On the other hand, in the Ahuachapán geothermal field (AGF), the samples were analysed using the old XRD machine, and by the time of acquisition of the new XRD, the field was already in stable condition and only once in a while samples are being collected. However, it was recommended to have the monitoring program similar to Berlín s program. Samples from clients (C), including external and internal clients other then AGF and BGF, have not reached full potential of the laboratory mainly because there isn t any publicity yet of the laboratory. Competition is only from the XRD machine donated to the university, however, some advantages of the Lageo laboratory are the machine is more modern and more reliable, and the analysis includes interpretation of data which makes the clients satisfied with the results, among which include the identification of treated and untreated clay minerals (especially kaolinite and halloysite) for pharmaceutical studies, deposition of scaling products (amorphous silica and
Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 154 calcite) in cooling systems, presence of corrosion products in pipelines of refineries, and identification of alteration minerals in some lithological formations in El Salvador. From this, the laboratory expects to increase its services to external clients to 10% from the present 4% (Figure 7) of the total analysis undertaken. Samples from different industries are now being accepted such as solid particles in air and water for environmental purposes, cement industry, construction, mining and metallurgy, paint industry, and refineries. XRD has also contributed a lot to the academe where scientific studies and thesis of graduating students in the universities were complemented by XRD analysis. Similarly, samples from the geological section (SNET) of the Ministry of Environment and Natural Resources are regularly analysed. Comparison of analysis (1999-2003) Distribution of samples analyzed 1999 to 2003 100% BGF AGF C 80% C AGF BGF 22% 4% 60% 40% 20% 74% 0% Figure 6. Comparison of analysis. Figure 7. Distribution of samples. FUTURE PLANS Some future programs for XRD are geared towards the following: A. Improvement of analysis of clay minerals; B. Certification of the laboratory; C. Improvement of the process of preparation of samples (separation of minerals, bulk and clay materials); D. Acquisition of new PDF files; E. Implementation of software for the quantification of minerals. CONCLUSIONS A. XRD has played an important role in geothermal in identifying mineralogical compositions of altered zones in volcanic areas, rock cuttings during drilling of wells, corrosion and scaling deposits in surface equipment and in wells; B. XRD has helped in the interpretation of hydrothermal processes occurring within and beneath the surface in both Ahuachapán and Berlín geothermal fields; C. XRD has opened its doors to clients. Samples from different industries are now being accepted such as solid particles in air and water for environmental purposes, cement industry, construction, mining and metallurgy, paint industry, and refineries; D. Samples from clients have not reached an ideal level, because there isn t much publicity yet for the laboratory. From a mere 4%, the laboratory expects to increase its services to 10%.
Copyright JCPDS - International Centre for Diffraction Data 2005, Advances in X-ray Analysis, Volume 48. 155 ACKNOWLEDGEMENTS I would like to thank Arturo Quezada and José Luis Henríquez for their valuable support, Aida de Zamora and Luz Barrios for their contribution and review during the write-up of this paper, and LaGeo S.A. de C.V. for giving me the opportunity to participate in this congress. REFERENCES [1] Zamora, A., E-mail Communication, 2004. [2] Rodriguez, J.A. and Herrera, A, Geothermal El Salvador, GRC Bulletin, July/August 2003, pp 159-162.