E. Santoyo

New improved equations for NaK, NaLi and SiO2 geothermometers by outlier detection and rejection

Abstract We present new improved equations for three still widely used Na K , Na Li and SiO 2 geothermometers (obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation) and compare them with those by Fournier and others. New equations are also developed for estimating errors associated with the use of these new geothermometric equations and comparing them with the performance of the original equations. The errors in the use of the new Na K equation for temperatures ranging from 80 to 350 °C vary from about 19 to 34%, which is lower than the corresponding errors (24–43%) for the original Fournier equation. Similarly, for temperatures ranging from about 50 to 320 °C, our new equation for Na Li geothermometer for Cl 2 2 geothermometer. We have proposed a linear equation for the temperature range of 210 to 310 °C (SiO 2 ≥ 295 ppm), which shows considerably smaller total propagated errors (2–3%) than for the original equation (5–29%).

Trace analysis of heavy metals in groundwater samples by ion chromatography with post-column reaction and ultraviolet-visible detection.

Groundwaters originating from local and regional aquifers surrounding ash deposits produced by a coal-fired power plant were collected. These water samples were chemically analyzed for quantifying their heavy metal composition at trace levels. A highly sensitive analytical technique based on ion chromatography with a UV-Vis detector and under isocratic eluent flow-rate conditions was used. In order to quantify the major heavy metals (Pb, Cu, Cd, Co, Zn and Ni), three ionic separation column systems were evaluated: (1) a cationic column (HPIC-CS2, Dionex) tested with two eluents (10 mM oxalic acid-7.5 mM citric acid; and 40 mM D-tartaric acid-12 mM citric acid); (2) an anionic column (HPIC-AS4, Dionex) evaluated with 25 mM oxalic acid as eluent: and (3) a bifunctional ion-exchange column (Ionpac CS5, Dionex) which was also tested with two eluents (6 mM pyridine, 2,6-dicarboxylic acid; and 50 mM oxalic acid/95 mM lithium hydroxide). The lowest detection limits achieved with the Ionpac CS5 column and the 50 mM oxalic acid-95 mM lithium hydroxide eluent enabled the heavy metal analysis in groundwater samples to be reliably performed. Details of this comparative study, including the ion chromatography procedure selected and its application to heavy metal analysis of groundwater samples, are presented in this work.

Rheological property measurement of drilling fluids used in geothermal wells

Abstract With the goal of increasing understanding of drilling fluid temperature behaviour during geothermal well drilling operations, and for providing a database for a better development of numerical wellbore simulators, an experimental work based on a rheological evaluation of drilling fluids was carried out. High-temperature drilling fluid systems (HTDFS) which are most commonly used in the Mexican geothermal well drilling industry were selected and evaluated. Eleven water-based drilling fluids were formulated and chemically characterised in order to carry out the rheological evaluation. Dynamic experimental tests considering the non-Newtonian behaviour of such HTDFS were performed using a coaxial cylinder-type viscometer (Fann 50C). Drilling fluid viscosities in a programmed temperature range of 25–180°C (at a constant reservoir pressure and a shear rate of 3448.2 kPa and 170 s −1 , respectively) were measured. These dynamic viscosity measurements were then fitted to derive correlating equations for determining the drilling fluid viscosity as a function of temperature. Details of the experimental rheological tests including a complete description of the equipment and all the HTDFS used as well as the derived viscosity–temperature equations are presented.

Improved capillary electrophoresis method for measuring rare-earth elements in synthetic geochemical standards

An improved capillary electrophoresis (CE) method for quantifying rare-earth elements (REEs) in synthetic geochemical standards was developed. Synthetic standard solutions were obtained from high purity metal oxides. The separation of REE total group (lanthanum to lutetium) was defined as a primary objective. Special attention was also focused on the optimized separation of europium (Eu) and gadolinium (Gd) because in earlier applications they presented overlapping problems. Their separation and quantitative determinations are essential for geological applications. For the rapid separation of REEs in synthetic geochemical standards, the temperature of the separation device was optimized. An analysis temperature of 15 degrees C enabled both the rapid separation of REEs within 2 min and the overlapping problem of Eu-Gd to be resolved. The detection limits (<0.1 ng) and precision estimates (generally better than 5%) were found to be satisfactory for most geological applications.

STATIC_TEMP: a useful computer code for calculating static formation temperatures in geothermal wells

Abstract The development and application of the computer code STATIC_TEMP, a useful tool for calculating static formation temperatures from actual bottomhole temperature data logged in geothermal wells is described. STATIC_TEMP is based on five analytical methods which are the most frequently used in the geothermal industry. Conductive and convective heat flow models (radial, spherical/radial and cylindrical/radial) were selected. The computer code is a useful tool that can be reliable used in situ to determine static formation temperatures before or during the completion stages of geothermal wells (drilling and cementing). Shut-in time and bottomhole temperature measurements logged during well completion activities are required as input data. Output results can include up to seven computations of the static formation temperature by each wellbore temperature data set analysed. STATIC_TEMP was written in Fortran-77 Microsoft language for MS-DOS environment using structured programming techniques. It runs on most IBM compatible personal computers. The source code and its computational architecture as well as the input and output files are described in detail. Validation and application examples on the use of this computer code with wellbore temperature data (obtained from specialised literature) and with actual bottomhole temperature data (taken from completion operations of some geothermal wells) are also presented.

TEMPLOP/V.2: a computer program for estimation of fully transient temperatures in geothermal wells during circulation and shut-in

This paper describes the development, validation and application of the TEMLOPI/V.2 computer program. This program is a useful tool for estimating in-situ the transient temperature distribution of the fluids employed for drilling geothermal wells. TEMLOPI/V.2 is based on a mathematical model which is developed to consider two-dimensional transient heat transfer during drilling and shut-in conditions in and around a geothermal well. The solution of the partial dierential equations is based on the finite-dierence technique with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Each radial grid node is placed in a dierent thermal region: flow inside the pipe, metal pipe wall, flow inside annulus, and the surrounding formation. The program was written in FORTRAN 77 using modular programming and runs on most IBM compatible personal computers. The software code, its architecture, input and output files, the solution algorithm, flow diagrams and source programs are described in detail. From validation tests, computed temperatures dier by less than 58C from analytically obtained temperatures. Comparison of results from the fully transient TEMLOPI/V.2 simulator and the pseudo-transient version, TEMLOPI/ V.1, with measured data shows that the fully transient model provides better results. Application of TEMLOPI/V.2 is demonstrated in a practical application study of well EAZ-2 from Los Azufres Mexican geothermal field. # 2001 Elsevier Science Ltd. All rights reserved.

An experimental integrated absorption heat pump effluent purification system. Part I: operating on water/lithium bromide solutions

Abstract The merits of single stage absorption heat pumps coupled to simple distillation for effluent treatment are discussed. An experimental integrated absorption heat pump effluent purification system (IAHPEPS) was built and operated with water–lithium bromide as a working mixture. This unit has been used to raise the temperature and hence, the vapour pressure of the impure water contained in one vessel, to the point where pure water vapour will distil from impure effluent solution (tap water or brine) and condense in a second vessel used to collect pure water. Pure effluent production rates of between 0.5 and 4.3 kg h −1 were obtained. The actual coefficient of performance ( COP A ) and the heat pump effectiveness varied from 1.1 to 1.4 and 0.58 to 0.72, respectively. The results from the small scale system indicate the likely results from industrial scale units which could be operated with low quality heat such as waste heat, solar or geothermal resources.

TEMLOPI: a thermal simulator for estimation of drilling mud and formation temperatures during drilling of geothermal wells

Abstract This paper describes the development and application of the numerical code TEMLOPI v1.0, a useful tool for estimating the temperature distribution of the fluids employed for drilling geothermal wells. The simulator also allows estimation of the thermal disturbance of the surrounding rock caused by fluid circulation and well shut-in. TEMLOPI v1.0 is based on a mathematical model which considers the main heat transfer mechanisms and the heat exchange between the circulating fluid and the surrounding rock formation that occur during drilling of geothermal wells. The simulator was written in Fortran 77 using modular (block) programming. It runs on most IBM compatible personal computers and can be used in-situ. Input data includes the well geometry, the fluid and flow characteristics and the initial (undisturbed) formation temperature. Output files contain the transient temperature distribution (temperature vs depth) in the fluid flowing down the drill pipe and the annulus, the well inner face and the radial distribution in the surrounding rock. The software code model, architecture, input and output files and the solution algorithm are described in detail. Results obtained were validated by comparison with data published in the specialized literature and with data from well Az-29 from the Los Azufres Mexican geothermal field.

Geochemical exploration of the Chipilapa geothermal field, El Salvador

Abstract Results of the geochemical exploration of the Ahuachapan-Chipilapa area are presented. The procedure for interpreting the chemical composition of very dilute thermal waters is emphasized. Three groups of thermal waters are described, two with a geothermal brine component and one resulting from steam condensation. The model for one of the groups (Type 2) leads to predictions of temperature and chloride concentration that are reasonably close to those of the geothermal liquid feeding Chipilapa well CH-7B. In particular, it was predicted correctly that the salinities in the Chipilapa area would be considerably lower than those in the Ahuachapan field.It is shown that the simultaneous modeling of the carbon dioxide concentration and isotopic composition of fumarole steam allows discrimination between primary and secondary steam. The composition of all fumarole samples is described as steam originating from a single reservoir fluid at 250°C, and composition δ 18 O = −4.1, δ D = −46, CO 2 = 5 × 10 −5 molar fraction.The total discharge composition of CH-7B confirms the trend observed in the Ahuachapan field of decreasing reservoir salinities towards the east. Postulating the existence of a “deep” reservoir brine in the eastern (Chipilapa) section of the system, with lower salinity but otherwise similar temperature and isotopic composition to the Ahuachapan brine, allows for the generation of relatively simple models that explain the formation of the CH-7B brine, and the three groups of thermal waters. Type 1 waters are noteworthy in the sense that they result from a ternary mixture of meteoric water, geothermal brine and high-temperature steam condensate.The possibility that the east-west trend in salinity results from a process of dilution of brine with condensate from steam separated at very high temperatures is discussed. The distribution of the different types of hydrothermal manifestations delineates a lateral discharge system, with the steam upflow zone to the south of the study area, on the northern slope of the volcanic range, and thermal water discharges several kilometers to the north. It is deemed reasonable that exploratory drilling should be directed towards the southern edge of the geothermal system, as far as topography and the indicators of probable secondary permeability permit.

Variability in the gas phase composition of fluids discharged from Los Azufres geothermal field, Mexico

Abstract Studies related to hydrological structure of the Los Azufres geothermal field and its effects on the exploitation of the field for generation of electrical energy have included a program of sampling and chemical analysis of fluids discharged by a number of deep wells in continuous production. Chemical analysis of the gaseous phase includes monitoring of CO 2 , H 2 S, NH 3 , H 2 , He, N 2 , CH 4 and 222 Rn. Five wells in Los Azufres field were periodically sampled during 1983–1988. The monitoring program has shown considerable variability in the gas concentrations of fluids. Before mid-1985, the ‘base-line’ concentrations of the gases showed standard deviations between 8 and 28%. During the later period, the average concentrations of different gases ranged from 37% to much higher values above the ‘base-line’. The largest variations are observed in He, CO 2 and 222 Rn. This variability is interpreted in terms of (1) addition of ‘excess steam’, (2) a possible relationship with earthquake events that occurred in Mexico during September 19–21, 1985, and early May to early June of 1987 and, (3) more recent variations (after mid-1987), increased exploitation of the field.