Thermophysical Properties Of Rocks Research Articles

SIMULATION OF THERMAL STUDIES IN A WELL ON THE SIMULATOR DRILLSIM

The paper presents the results of studies in the well conducted specifically for testing the technique of restoring the equilibrium temperature of rocks by measured transient temperature distributions in the well. The technique is based on numerical simulation of heat exchange processes during flushing of a long-idle well and subsequent solution of the inverse problem. A depth temperature measurement was carried out in an idle well (geothermal distribution) and a series of depth temperature measurements were carried out immediately after washing after 3, 6, 9 and 12 hours. After the experiment, numerical simulation of the temperature recovery process after flushing was carried out. To do this, a simulator was developed that takes into account the thermophysical properties of rocks and mudliquid, the design of the well, as well as the history of the well. Based on the developed simulator, it is proposed to implement a solution to the inverse problem of determining the equilibrium temperature of rocks from the measured non-stationary distributions after its perturbation. As shown in the paper, the developed algorithm makes it possible to determine not only the geothermal temperature distribution, but also the flow rate of the mud liquid in the borehole during the flushing process.

Deep bedrock geothermal resources in the Maichen Sag, Beibuwan Basin and their potential for exploitation and utilization

The Maichen Sag in the south-central part of the Beibuwan Basin is abundant in geothermal resources that have not been widely exploited and utilized due to inadequate research on it. This study evaluated the geothermal resources in the Maichen Sag based on the regional geological setting and geothermal conditions. Grid units for assessment and a geological model for areas with geothermal resources were established using spatial analysis techniques. The spatial distribution models of the physical and thermophysical properties of the geothermal reservoirs were also built using the Kriging interpolation method. Based on the terrestrial heat flow distribution in the target areas, the spatial distribution of the geo-temperature field through the inversion under the constraints of the temperature data from boreholes were predicted. Factors such as deep geo-temperature, thermophysical properties of rocks, and terrestrial heat flow values, were integrated into this quantitative evaluation of geothermal resources through the geological modeling-based volume method and the geothermal reservoir engineering-based numerical simulation method. The results show that the Maichen Sag has favorable heat source conditions with intersected, deep-rooted faults and widely developed Upper Paleozoic fissured granite geothermal reservoirs. The northern outer slope zone at a burial depth of 3‒5 km on the tectonic plane of the basement in the sag is suggested to be a potential target area, where, as calculated using the volume method, is likely to be the home to the total geothermal resources of 80.4×109GJ (i.e., 2.75×109tonnes of coal equivalent (tce)) in the bedrock geothermal reservoirs at a burial depth of 3‒6 km. The geo-temperature of 172‒201°C at a formation depth of 5 km in the sag also indicates that the deep geothermal resources are of high value for exploitation.

Prediction of the temperature distribution in the reservoir when oil is displaced by a fluid with a temperature different from the reservoir

The temperature field is an important factor that must be considered when using thermal methods to intensify oil production. The change in the temperature field is accompanied by a change in the thermophysical properties of reservoir fluids and the entire bottom-hole zone. For example, changes in fluid viscosity, phase transformations or paraffin deposition. The prediction of the thermal field in the reservoir during fluid injection with a temperature other than the reservoir is an important and actual task. All the processes described above are based on the prediction of the temperature field and its evolution. Non-isothermal filtration models embedded in expensive commercial simulators are used to analyze the thermal field in formations, which allow calculating its detailed evolution in geologically complex deposits. However, many tasks are reduced to determining the probability of activation of a particular thermal process in the reservoir. Therefore, the purpose of this work is to develop a simplified model of the evolution of the thermal field in the reservoir during fluid injection with a temperature different from the reservoir. In this paper, the stationary problem of the distribution of fluid temperature in the injection well trunk is solved. An algorithm for determining the heat transfer coefficient by measuring the temperature at the bottom of the well has been developed. A simplified model of the formation of a temperature field in a reservoir during the injection of a fluid with a temperature different from the reservoir in the Lauwerier approximation is formulated. The formula for determining the average value of the heat transfer coefficient along the entire length of the formation is obtained. It is shown that the heat transfer coefficient depends on the thermophysical properties of the injected fluid and the parameters of the injection well operation. It is shown that the absence of measurements of the thermophysical properties of rocks and reservoir fluids leads to predictions of the thermal field with maximum uncertainty in the half of the impact site closest to the injection well.

Geocryological conditions of the Tokarikan and Guvilgra grabens (South Yakutia)

This article presents the results of geocryological studies of the Tokarikan and Guvilgra grabens of the Aldan Shield. Expedition research on the hard-to-rich region since 1996 has allowed us to determine the temperature regime, thickness, and nature of permafrost rock distribution and characterize its geocryological conditions for the first time. We have established that the lowest temperatures (up to –3.4 °С) are characteristic of peatmoss bog landscapes, whereas the highest (–0.5 °С) are for well-drained and watershed areas. The results of the measurements in deep wells, information on the process of drilling deep exploration wells, and the analysis of data on the thermophysical properties of rocks allowed us to estimate a permafrost thickness capacity that varied in the range of 40–260 m. The presented schematic permafrost and geological cross-sections and geocryological condition maps can be used to plan the industrial development of the territory.

Search for promising locations to explore geothermal resources based on joint analysis of sections of petro- and thermophysical properties of rocks

The purpose of the study is identification of locations promising for geothermal resource exploration based on the joint analysis of sections of petro- and thermophysical properties of rocks. Having conducted magnetotelluric sounding in the geothermal area under investigation and having built 2-D models of electrical resistivity, porosity, permeability, temperature, thermal conductivity and specific heat capacity, the authors performed a joint cluster analysis of sections of enumerated parameters. A cluster cross-section is constructed taking into account all the discussed parameters, which is essentially a petro- and thermophysical “passport” of the site under examination. Each cluster of the latter is characterized by its own set of property ranges. Two promising locations for drilling exploratory boreholes have been identified in the Soultz-sous-Forêts (France) geothermal area. One of them corresponds to the already developed reservoir of petrothermal energy, while another is located at the depths of 2–3 km in another part of the section and has a potential for future exploration works. The information base created on this basis is a convenient tool for interactive selection of sites promising for exploration of different deposits and building of a “prospectivity map” of surface sites for drilling exploration boreholes.

New estimates of the influence of paleoclimate on the vertical distribution of heat flow

The study of deep continental boreholes revealed significant vertical variations in heat flow. This fact still has no satisfactory explanation. One possible cause could be the effects of past climate changes, namely changes in the Earth's surface temperature. The paper discusses some consequences of accounting for the influence of paleoclimate on the measured heat flow using the example of the platform part of the Republic of Bashkortostan. A numerical simulation of the influence of paleoclimate on the distribution of the thermal field in the borehole was performed using two models of past climate changes. The first model, adopted earlier, includes two major climatic episodes of the past, the Würm glaciation 80–10 thousand years ago, and the Little Ice Age, 600–150 years ago. The second model uses the climatic curve for the Meso-Cenozoic, which additionally takes into account the warming that began about 65 Ma, reached its maximum about 45 Ma, and followed by a cooling that continued with some fluctuations until the present time [Velichko, 1987]. It is shown that, in the analysis of vertical variations in heat flow, the use of a model of past climate changes, taking into account more distant large climatic events than has been done previously, allows us to estimate the paleoclimate influence as much more significant than previously thought. However, at this stage of the research, with the accepted models of temperature changes at the Earth's surface, the vertical variations of the heat flow established by the results of experimental geothermal studies cannot be explained only by the influence of the paleoclimate. To solve the problem, we need a detailed study of the thermophysical properties of rocks, high-quality temperature measurements in wells, and improvement of the model of past climate changes in the region under study.

Instrumentation complex for measuring the thermophysical properties of rocks in natural occurrence temperature conditions

A schematic diagram and an operation algorithm of an instrumentation complex for measuring the thermal conductivity and thermal diffusivity of rocks by the non-stationary method of a linear source under natural occurrence temperature conditions up to 200 °C are proposed. Thermocouples are used to measure the temperature of the probes. The complex contains two linear (needle) probes, which are placed in a rock sample at a certain distance r from each other. One probe, containing a linear heater and a thermocouple, radiates heat, the other one, containing a thermocouple, is a measuring probe. The cold junction temperature of thermocouples is measured by a semiconductor sensor. To calculate the voltage of the cold junction from the value of its temperature, a direct conversion of thermoEMF by a power polynomial is used. To calculate the temperature of the hot junction of the probe, an inverse transformation by a power polynomial of the voltage values of the hot junction of thermocouples into temperature was applied. In direct and inverse transformations, the degree of polynomials is 10. To reduce the temperature measurement error, digital filtering of signals from thermocouples was used. A digital-to-analogue converter is included in the heater circuit of the radiating probe for flexible heating control. The results of measuring the thermal conductivity and thermal diffusivity of dry and wet sand samples are consistent with the literature data on the temperature dependence.

Geophysical Analysis of Thermo-physical Properties of Rocks in Ikogosi field for Geothermal Energy Prospect.

The thermal and physical properties of rock units from Ikogosi Warm Spring (IKGWS) in the Southwestern part of Nigeria were examined in order to characterize and explore its geothermal prospect and to provide an insight into the different thermal properties of rocks of the study area. A total of 40 rock samples made up of granite, quartzite and gneiss series were collected from the outcrops of the study area and analyzed for Thermal conductivity (TC), Radiogenic heat production (RHP), Heat flow (HF), Porosity, Density and surface spring temperature measurements. The RHP values for all samples varied from 1.8 to 3.5μWm-3 with an average value of 2.5μWm-3 and standard deviation (SD) of 0.4 while the heat flow values varied from 14 to 27mWm-2 with an average of 19mWm-2 and SD of 3.4. The TC values varied from 2.95 to 4.11 with a mean of 3.49mWK-1 with a SD of 0.4 while the porosity values varied from 0.21-1.15 % with a mean of 0.62% with SD of 0.39. The density values varied from 2.68 to 2.85gcm-3 with a mean of 2.76gcm-3 and SD of 0.067. The surface temperature of the spring varied from 32 to 45°C with a mean of 38.9°C. From these results the average RHP and HF values estimated from all samples was below the 4μWm-3 and 100mWm-2 recommended value of heat to be considered for economic importance. Thus, the IKGWS geothermal field cannot be explored for power generation but for other geothermal activities and may be classified as a low enthalpy geothermal system (

Thermal Property of Granite in Deep Strata and Its Effect on Thermal Zone of Surrounding Rock

In order to clarify the changes in the thermophysical properties of rocks in deep high-temperature strata and their influence on the temperature field of the surrounding rocks, thermal property tests were conducted on rock samples taken from 1,500 to 2,000 m depth in the Xiling well construction area of Sanshandao gold mine. According to the difference equation based on the principle of heat balance, the numerical solution of unsteady heat conduction of surrounding rock can be deduced. In addition, we can explore the dynamic process of the heat-regulating ring that under ventilation measures in deep high geothermal strata and analyze its influence on the dynamic process based on the equation. The result of the research shows that the thermal conductivity of rock is mainly determined by the mineral composition and is influenced by factors such as mesostructure. Calcite and muscovite of granite have a great impact on lithology, even they just account for a relatively small percent. As the ground temperature increases step by step, the variation of the thermal conductivity of rock is less and the thermal diffusion coefficient of rock and its ability to transmit temperature changes both decrease. On the contrary, as the specific heat capacity of rock increases, its heat storage capability enhanced. Therefore, the expansion range of the heat-regulating ring of surrounding rock is influenced by mineral composition and the temperature of the environment, and the influence of the former is much greater than the latter.

Експериментальні дослідження теплофізичних властивостей гірських порід

Purpose. Obtaining data on the thermophysical properties of rock samples of PJSC “CG Pokrovske” under normal conditions in order to increase the versatility of methods for determining the location of the fire source, the location of the fire in the produced space, obtaining an assessment of its condition and monitoring control at various stages of combustion. Research methodology. The article is aimed at studying the characteristics of heat transfer in rocks, in particular at determining the thermophysical properties of rocks, for which experimental studies of thermal conductivity, thermal conductivity and specific heat capacity of rock samples of the Pokrovska mine were carried out with the help of a thermal conductivity analyser TНВ-100 and the influence of humidity on their thermal conductivity was determined properties using the MIT-1 thermal conductivity meter. Results. The obtained data on thermal conductivity, thermal diffusivity and specific heat capacity of siltstone, sandstone and coal samples taken from the “CG Pokrovske” can be used to improve the existing methods of finding the source of the fire and its location in the mined space, as well as to assess and control the state of the fire. The result of such an improvement can be any work in which it is possible to obtain a more universal way of assessing the state of the fire – the fact of an extinguished or burning fire, the temperature in the fire zone, determining the location of the coal ignition centre and, in fact, the fire itself in the mined space. Scientific novelty. It has been established that with an increase in the weight humidity of rock samples, there is a proportional increase in their thermal conductivity, which is explained by the fact that with an increase in humidity, the latter improves thermal contact in places where particles collide, where, first of all, moisture gets into the smallest pores of the material and displaces air from them. Practical significance. In mines, great importance is given to the forecast of temperature indicators when measuring the temperature of the fire rock in the excavation to assess the process of fire development in order to extinguish them as quickly as possible. These indicators are important for the actual assessment of the state of the environment in the centre of its extinguishing, as they are control for determining the cooling of the rocks of the massif and, ultimately, indirectly indicate the fact of a burning or extinguished fire. The thermophysical properties of rock samples obtained as a result of experimental studies make it possible to increase the versatility of fire assessment methods at various stages of its combustion and, in general, to increase the level of endogenous fire safety of coal mines.

Физико-математическая модель и метод расчета процессов тепломассопереноса в системе пласт--горизонтальные скважины

In order to solve scientific and engineering problems arising during analysis and development of hard-to-recover hydrocarbon reserves in high-viscosity oil deposits, we performed a numerical study of heat and mass transfer processes in a mixture of water and oil. We achieved these goals by developing a hydrodynamic and thermophysical model of non-steady-state quasi-three-dimensional heat and mass transfer in a stratum featuring a system of horizontal wells. We propose an analytical approach to plotting a dynamic computational grid in a natural semi-fixed coordinate system. We compute streamlines and equipotential lines using the analytical solution proposed, which is based on complex analysis. The object of our investigation is natural strata saturatedby a multiphase fluid. We used the physical and mathematical model and the calculation method proposed to develop a software package and conduct a series of numerical and parametric studies concerning the effects caused by thermophysical properties of rocks and fluids combined with various operation modes in a system of horizontal wells. The paper describes how these parameters affect the rate of oil production in a real high-viscosity oil deposit. We verified the results obtained against actual core sample investigation data and technological parameters of oil deposit development, and further compared them to known analytical solutions and commercial hydrodynamic simulators

Application of the steаm аssisted grаvity drаinаge (SAGD) method in the heavy oil fields

Recently, the prospects for the development of the oil industry have been associated with the development of deposits of heavy oils and natural bitumen. It is economically feasible and possible to extract high-viscosity oil (HVO) and natural bitumen (NB) only thanks to the development and application of effective technologies for their development. Unconventional oil production requires an unconventional exclusive approach, one of them is the steam — gravity method of oil production. The creation of SAGD models involves solving problems of heat and mass transfer in wells and a productive reservoir to optimize the production mode. To calculate the parameters of heat transfer, reliable information is required about the complex of thermal properties (thermal conductivity, thermal conductivity, volumetric heat capacity) of rocks of the productive formation, the underlying and overlapping layers of the mountain massif. Currently, when conducting research and constructing geological and technological models for predicting development indicators, the degree of influence of variations in the thermophysical properties of reservoir rocks on the efficiency of the SAGD process is not taken into account. Due to the absence until recent years of the possibility of obtaining reliable representative data on the thermal properties of rocks of a particular deposit, averaged values based on single measurements or on reference data that do not take into account the features of the object being developed and do not contain a detailed geological description of the studied rocks are usually used. In this regard, it was necessary to conduct a study of the influence of real spatial variations of the thermophysical properties of rocks, studied in detail for one of the deposits with the help of a new highly efficient hardware and methodological measuring base, on the development indicators by the SAGD method. In this article, the authors considered the effectiveness of using horizontal wells with cyclic steam exposure at the Yareg field.

Moisture and Temperature Response of Structural and Lithology based Thermophysical and Energy Saving Traits of Limestone using Experimental and Least-Square Fitting Methods

Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings. In the presented work, thermophysical properties of four limestones were investigated in dry and moist state under ambient conditions by using a transient plane source method. A thermal constant analyzer was used to raise the sample temperature and to measure the thermal properties in the temperature range of 300 K to 433 K. Thermal conductivity and diffusivity were measured by developing a linear relationship between temperature response of TPS (transient plane source) sensor and dimensionless time function through least-square fitting method. The experimental observations and predicted thermal conductivity of samples have shown that in-situ observations are important to determine the thermal properties accurately. The effect of temperature on thermal properties of limestone was defined by considering the chemical composition of the samples and associated heat transfer mechanism. Both thermal conductivity and diffusivity of limestone decreased while specific heat capacity increased with a rise in temperature. The overall findings indicate that the spinoff of this research is useful in studying the reliance of thermophysical properties of rocks on their structures and lithology.

Thermal Interaction of a Gas Well Cluster with Permafrost Rocks of the Most Promising Deposits of Central Yakutiya

The results of a numerical experiment to determine the thermal impact of a gas well cluster on permafrost rocks are given for the conditions of four deposits of Central Yakutiya, Middle-Vilyuy (Srednevilyuiskoe), Middle-Tyung (Srednetyungskoe), Sobolokh–Nidzhili (Sobolokh-Nidzhilinskoe), and Tolon–Mastakh (Tolon-Mastakhskoe). An approximate mathematical problem is solved in a conjugate formulation. In this case, the process of melting of permafrost rocks is described within the framework of a three-dimensional Stefan problem, and the motion of real gas in wells is described within the framework of tubular hydraulics. Use has been made of real data for temperature well logging, formation pressure and temperature, well flow rate, gas composition, and thermophysical properties of rocks. The melting of frozen rock depending on the depth and time has been calculated, and instants of time for linkage of thaw zones of neighboring wells have also been computed.

РАСЧЕТ PVT-СВОЙСТВ ДОБЫВАЕМОЙ ПРОДУКЦИИ ПО ДЛИНЕ ПОДЪЕМНИКА

Актуальность. Все технологические процессы, происходящие в пласте, стволе скважины и в системе сбора и подготовки нефти, газа и газоконденсата, требуют знания физико-химических свойств добываемой скважинной продукции. С этими параметрами связаны запасы углеводородов, изменение состава пластовой смеси, темп вторжения воды в залежь, парциальное давление отдельных компонентов, конструкция скважин, гидравлические потери, подбор оптимального режима эксплуатации и т. д. Все технологические процессы добычи, сбора, подготовки и транспортировки сопровождаются непрерывным изменением давления и температуры, которые непосредственно влияют на свойства продукции, «PVT-свойства». Отсутствие представлений о физико-химических свойствах и фазовых превращениях, протекающих при изменении термобарических условий в многокомпонентных системах, приводят к принятию неверных технологических решений, возникновению осложнений в процессе эксплуатации скважин и, как следствие, снижению эффективности разработки месторождения. Поэтому так важно уметь прогнозировать изменение давления и температуры и рассчитывать PVT-свойства по пути движения флюидов. Целью данной работы является расчет и анализ изменения PVT-свойств добываемой продукции и температуры по длине скважины. Методы. Для расчета плотности и вязкости нефти, объемного коэффициента нефти, растворимости и коэффициента сверхсжимаемости применена методика М.Б. Стэндинга, разработанная в США в результате многочисленных исследований проб нефти и газа, для расчета кривой изменения температуры по глубине скважины был использован метод И.Н. Алвеса. Выводы. Растворимость газа линейно увеличивается с ростом давления, который также вызывает увеличение газосодержания и, соответственно, объемного коэффициента. В свою очередь, повышение газосодержания нефти приводит к плавному снижению плотности. С ростом температуры по стволу скважины происходит снижение вязкости нефти. Изменение термобарических условий обуславливает снижение коэффициента сверхсжимаемости по глубине скважины. Методика Алвеса не позволяет точно спрогнозировать изменение температуры по стволу скважины, что объясняется сложностью учета теплофизических свойств горных пород и флюидов.

RETRACTED ARTICLE: Analysis of the relationships between the thermophysical properties of rocks in the Dandong Area of China

ABSTRACT Data of this paper analysis indicates that the thermal conductivity increases with increasing water content. X-ray diffraction was used to analyze the mineral compositions of the rock samples. The rock samples were found to contain quartz, alkali-feldspar, and plagioclase. A theoretical equation was applied to calculate the skeleton thermal conductivity (λs )of the rocks in the Dandong region and the thermal conductivity of the saturated rocks (λsat )after conversion occurred, which were later compared to the quartz content. The quartz content was found to positively correlate with the skeleton thermal conductivity. Scanning electron microscopy was used to obtain images of the rock samples, which were used to determine the microscopic structure of the different rock types and to determine the relationship between the thermal conductivity and the porosity. We determined that the mineral content and porosity of igneous rocks is far higher than that of sedimentary rocks, and the thermal conductivity of igneous rocks is generally higher than that of sedimentary rocks. The relationship between thermal conductivity and porosity was investigated using eight different thermal conductivity-porosity models. The results indicate that thermal conductivity decreases with increasing porosity.

Satellite-Derived Regional Apparent Thermal Inertia and Gravity for Mapping Different Rock Types in Parts of Banswara, Rajasthan

In this study, utility of satellite derived Apparent Thermal Inertia (ATI) and residual gravity data have been analyzed for delineating the major rock types of Aravalli Supergroup. Density is a common contributing factor responsible for ATI and gravity variations of rock types. In addition to density, thermal inertia is also controlled by specific heat and thermal conductivity. In the present study, MODIS (Moderate resolution imaging spectrometer) day and consecutive night time land surface temperature (LST), albedo data have been processed to derive ATI image for the study area. On the other hand, Bouguer gravity generated from EIGEN6C4 gravity model data is processed to derive the residual gravity over the study area. It has been observed that ATI values of different rock types are influenced by the variations in weathering pattern and forest cover developed over the rock in addition to the thermophysical parameters of rocks. Forest cover and agricultural activity are responsible for shifting the ATI values to higher side for any rocks due to evapotranspiration; which is responsible for reducing day and night land surface temperature difference. ATI pixels( collected from large rock pavements) of different rocks can however, be used to discriminate them from each other. Conjugate analysis of residual gravity and ATI has been proved useful to discriminate different rock types of spatially well distributed rock exposures. It is found that ATI and gravity values are well correlated for the spatially large surface exposures of rocks. In regional scale, low frequency changes of ATI broadly matches with the changes observed on the corresponding spatial profiles of residual gravity with some localized variations. This is due to the fact that shallow surface gravity anomaly is cumulative effect of vertical and horizontal variations of density in contrast to ATI which is more sensitive to near surface density, conductivity and specific heat variations of rocks. Moreover, high frequency variations imprinted on regional ATI spatial profiles are due to the cumulative effect of complex thermophysical properties of surface elements (weathering residuum, surface moisture variations) density variation and intrinsic thermophysical properties of rocks measured at regional scale. High frequency changes of ATI do not correspond well with residual gravity variation.

Outcrop analogue study to determine reservoir properties of the Los Humeros and Acoculco geothermal fields, Mexico

Abstract. The Los Humeros geothermal system is steam dominated and currently under exploration with 65 wells (23 producing). Having temperatures above 380 ∘C, the system is characterized as a super hot geothermal system (SHGS). The development of such systems is still challenging due to the high temperatures and aggressive reservoir fluids which lead to corrosion and scaling problems. The geothermal system in Acoculco (Puebla, Mexico; so far only explored via two exploration wells) is characterized by temperatures of approximately 300 ∘C at a depth of about 2 km. In both wells no geothermal fluids were found, even though a well-developed fracture network exists. Therefore, it is planned to develop an enhanced geothermal system (EGS). For better reservoir understanding and prospective modeling, extensive geological, geochemical, geophysical and technical investigations are performed within the scope of the GEMex project. Outcrop analogue studies have been carried out in order to identify the main fracture pattern, geometry and distribution of geological units in the area and to characterize all key units from the basement to the cap rock regarding petro- and thermo-physical rock properties and mineralogy. Ongoing investigations aim to identify geological and structural heterogeneities on different scales to enable a more reliable prediction of reservoir properties. Beside geological investigations, physical properties of the reservoir fluids are determined to improve the understanding of the hydrochemical processes in the reservoir and the fluid-rock interactions, which affect the reservoir rock properties.

Petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the Guadeloupe Archipelago (West Indies)

The results of the GEOTREF project presented here aim to develop high enthalpy geothermal energy in fractured reservoirs. They focus on active volcanic islands, especially the Basse-Terre Island (Guadeloupe Archipelago). As part of this project we measured several petrophysical properties to better understand how fluids flow in the hydrothermal system, provide a set of parameters to modelers and build datasets for future interpretation of well logs. The thermo-physical rock properties of bulk and grain density, porosity, permeability, compressional wave velocity, thermal conductivity and diffusivity, specific heat capacity of outcropping volcanic rocks from the Guadeloupe Archipelago (Lesser Antilles) were measured and a dataset was built. According to field observations, samples were grouped into three lithological classes and then separated by their degree of alteration according to macroscopic aspects and optical microscopy results. Geochemical data were obtained, and magnetic minerals identified by combining anisotropy of magnetic susceptibility and variation of magnetic susceptibility with temperature.The lithotypes investigated were lava flows, debris flows and pyroclastics (gathering ash, pumice and scoria deposits). For lavas and debris flows, three degrees of alteration were defined; fresh, slightly to moderately altered and highly hydrothermalized. Only fresh pyroclastics were studied because the altered state was not outcropping.Typically, samples are composed of andesite and belong to tholeiitic and calc-alkaline series. Lava porosity consists of high-density cooling joints and vesicles of different shapes, whereas pores in debris flows and pyroclastics are located both between and within particles. Median porosities and permeabilities are clearly distinct for lavas (4% and 6 · 10−18 m2), debris flows (33% and 4 · 10−14 m2) and pyroclastics (34% and 8 · 10−13 m2). The porosity difference implies a thermal conductivity twice to three times higher for lavas (1.68 W·m−1·K−1). Specific heat capacity of all lithothypes is similar (0.75–0.97 kJ·kg−1·K−1).Advancing hydrothermal alteration removes magnetic minerals and transforms initial rocks. The original plagioclases and pyroxenes in neoformed chlorite, white micas, quartz, epidote and clay minerals are replaced. This modifies the shape of the pore network. Furthermore, hydrothermal alteration results in a reduction of pore throat diameter. It tends to decrease petrophysical differences between lavas and debris flows, increasing the porosity and permeability of effusive rocks, while the opposite effects are observed for debris flows.

Thermo-physical rock properties of greywacke basement rock and intrusive lavas from the Taupo Volcanic Zone, New Zealand

Greywacke of the Waipapa and Torlesse (Composite) Terrane form the basement of the Taupo Volcanic Zone (TVZ), New Zealand. Together with inferred buried lavas, domes and igneous complexes they are likely to be the dominant rock type prevailing at depths >4km beneath the TVZ. A fundamental understanding of the rock properties of the deep formations is of utmost importance for the exploration of deep unconventional geothermal resources. An outcrop analogue study was conducted to improve the understanding of the thermo-physical rock properties of likely deep buried rock formations beneath the TVZ. A total of 145 core samples were taken at 10 locations inside and outside the TVZ and their grain and bulk density, porosity, matrix permeability, bulk thermal conductivity and specific heat capacity, and the compressional and shear wave velocities measured on oven-dry samples. Additional tests of the unconfined compressive strength were conducted for selected greywacke samples to quantify their mechanical rock strength.The obtained data indicates that the thermo-physical rock properties are mainly controlled by porosity, and minor by mineralogy, texture and grain size. Samples from Waipapa-type and Torlesse-type greywacke exhibit minor rheological differences, with Waipapa-type greywacke having lowest porosity (about 1% vs. 3%) and highest bulk thermal conductivity (2.5Wm−1K−1 vs. 1.7Wm−1K−1) and specific heat capacity (0.8kJkg−1K−1 vs. 0.7kJkg−1K−1). Matrix permeability is <1E-16m2 for all greywacke samples. Tested lavas exhibit heterogeneous rock properties due to their wide range of porosity (<1% up to 32%).The thermo-physical rock properties were tested at laboratory conditions (ambient temperature and pressure), which do not reflect the in situ conditions at greater depth. With depth, thermal conductivity and acoustic wave velocity are likely to decrease caused by micro fractures resulting from thermal cracking of the rock, while specific heat capacity increases.The data presented in this paper are expected to improve the statistical confidence on input data to geophysical and thermo-hydro-mechanical numeric models, and the ability to forecast rock properties at greater depths of the TVZ.