AN INVESTIGATION OF WELLBORE SCALING AT THE MIRAVALLES GEOTHERMAL FIELD, COSTA RICA

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Miravalles geothermal field lies in the Guanacaste province of Costa Rica in Central America. At the time of the study (late 1982), three wells (named PGM-1, PGM-2 and PGM-3), had been drilled and periodically tested in this field during 1980-82. During several of these tests scaling of the wellbore appeared to be a serious problem. This paper presents a portion of a study conducted to define the nature and causes of the scaling problem. No new data were gathered during this study; it was based on the analysis of already existing data as of late 1982. The main limitations in ... continued below

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37-44

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Sanyal, S.K.; McNitt, J.R.; Klein, C.W. & Granados, E.E. January 22, 1985.

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Miravalles geothermal field lies in the Guanacaste province of Costa Rica in Central America. At the time of the study (late 1982), three wells (named PGM-1, PGM-2 and PGM-3), had been drilled and periodically tested in this field during 1980-82. During several of these tests scaling of the wellbore appeared to be a serious problem. This paper presents a portion of a study conducted to define the nature and causes of the scaling problem. No new data were gathered during this study; it was based on the analysis of already existing data as of late 1982. The main limitations in the data as regards this study were: (1) no bottomhole pressure measurements had been made; (2) no temperature or pressure profile under flowing condition was available from any well; (3) a wellhead separator was available at only one well (PGM-1); and (4) although James' lip pressure measurement facilities were available at all wells, in some of the earlier tests (up to May 1981) no measurement of the liquid flow rate was made. The fact that there was scale deposition in the Miravalles wells was indicated by several observations: (1) unusually rapid decline had been experienced in both flow rate and wellhead pressure (p{sub wh}) except when the wells were flowed at a relatively high p{sub wh} level. For example, Figure 1 presents the situation for well PGM-1 during a test (Test 1). This behavior was not due to reservoir depletion because the wells produced a much larger cumulative mass without a serious drop in flow rate or p{sub wh} when flowed above a certain p{sub wh} level, whereas a much smaller cumulative production was possible if a lower p{sub wh} level was maintained. Only a part of the decline in mass flow rate in some of the tests had been caused by increasing steam fraction in the produced fluid. (2) The decline in flow rate became precipitous towards the end of some of the tests. Yet, there had been no precipitous decline in reservoir pressure. For example, on being shut in after several weeks of wide open discharge in 1981, the water level in well PGM-1 returned quickly to the original static level. (3) In May 1981, caliper logging indicated that the borehole diameters in PGM-1 and PGM-3 were reduced sharply after a few months of flow (Figure 2).

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37-44

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  • 10. annual workshop on geothermal reservoir engineering, Stanford, CA (US), 01/22/1985

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  • Report No.: SGP-TR-84
  • Report No.: CONF-850107-14
  • Grant Number: AS03-80SF11459
  • Office of Scientific & Technical Information Report Number: 892134
  • Archival Resource Key: ark:/67531/metadc875583

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  • January 22, 1985

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  • Sept. 21, 2016, 2:29 a.m.

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  • Dec. 7, 2016, 3:44 p.m.

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Sanyal, S.K.; McNitt, J.R.; Klein, C.W. & Granados, E.E. AN INVESTIGATION OF WELLBORE SCALING AT THE MIRAVALLES GEOTHERMAL FIELD, COSTA RICA, article, January 22, 1985; United States. (digital.library.unt.edu/ark:/67531/metadc875583/: accessed September 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.