Fluid Rock Research Articles

Superelevation analysis of the debris flow curve in Xiedi gully, China

The superelevation phenomenon is common in the movement of debris flows around curves. This paper presents a new method to calculate the superelevation of debris flow when it encounters obstacles in the flow process. The calculation method is based on the Bingham Model for debris flow determination. In this paper, physically significant internal and external roughness coefficients are determined by analysing the internal characteristics and external channel boundary conditions of viscous debris flows in Xiedi gully, China. According to the situation of debris flow passing through the bend, when the debris flow moves to the sidewall of the gully with velocity, the movement state is divided into two parts: radial and normal. One part of the mud rock fluid continues to move in the tangential direction and generates superelevation, and the other part moves in the radial direction and generates upward climbing along the sidewall. Thus, the formula for calculating the superelevation of debris flow bend is derived. Based on the debris flow physical and dynamic parameters, such as density and weight of the debris flow, cohesion, internal friction angle, yield stress and dynamic viscosity of liquid-phase slurry, the reliability of the formula is verified, which provides a theoretical basis for future studies of debris flow disaster prevention and control in similar areas.

Mineralogy, Fluid Inclusion and H‐O‐C‐S Stable Isotopes of Mengqiguer Uranium Deposit in the Southern Yili Basin, Xinjiang: Implication for Ore Formation

AbstractThe Mengqiguer deposit in the southern Yili basin Ili Basin is a large interlayer‐oxidation‐zone type uranium deposit. In this paper, we applied multiple methods including microscopic observation, scanning electron microscope and electronic probe, to analyze the systematical alteration characteristics of the ore‐bearing sandstone layer. Fluid inclusion and stable isotope studies on the ore‐bearing sandstone have also been carried out to discuss the internal relations between fluid activities, epigenetic alteration and the uranium mineralization. Major epigenetic alteration include clay alteration, carbonatization and pyritization, of which biogenetic pyritization is most closely related to the uranium mineralization. This suggests the existence of microorganism during the uranium mineralization process. The mineralization fluids of low temperature, medium density but varied salinities are suggested to be derived from multi‐source, including the meteoric water and organic acidic vapor components from coal‐bearing strata. Uranium mineralization, grain‐dispersed kaolinite, limonite, colloidal pyrite, and the carbonate cements associated with sulfate‐reducing bacteria were formed by meteoric water and vermicular‐shaped kaolinite, autologous pyrite, and the carbonate cementation associated with the dehydroxylation of organic matter was formed by organic acidic. Based on these results, we consider that the uranium mineralization and epigenetic alteration both resulted from the reciprocity of organic–inorganic fluid and fluid–rock during the formation of the interlayer oxidation zone.

Mineralogy, fluid inclusions and carbon isotopes of the Kaman iron deposits, Central Anatolia, Turkey: Implication for ore genesis and hydrothermal evolution

The Kaman iron deposits are located in Central Anatolia and are hosted by the Triassic Bolçadağ Marble and Upper Cretaceous Çelebi granitoid. Magnetite mineralization manifests as rhythmic banded and irregular lenses, which can be massive or disseminated within calcic marble and skarn zones. Six main paragenetic stages of skarn formation and ore deposition have been identified: (1) Na-(Ca) alterations composed of plagioclase (An4–31), and actinolite; (2) a prograde stage representing oxidized mineralogy dominated by diopside (Di62–98Joh0–4), grossular–andradite (Grs15–84Alm4–8Sps1–4) and magnetite; (3) a retrograde stage consisting of epidote (Ep51–62Cli38–49), magnetite, calcite, quartz, and less-abundant sulfides and chlorite; (4) a quartz-calcite-pyrite stage containing pyrite, quartz, calcite, and chlorite; and (5, 6) quartz-carbonate and supergene stages characterized by quartz, calcite, hematite, and chalcedony, goethite.Fluid inclusion and carbon isotope studies have shown that the prograde stage formed from moderate–high-salinity (7.1 to >70 wt% NaCl eq.) and high-temperature (339 to >600 °C) fluids. Liquid and vapor-rich inclusions in an early garnet were homogenized in the liquid and vapor phases in a similar temperature range (513 and 529 °C). The δ18O and δ13C of calcites that accompany rhythmic banded magnetite ranged from 22.82 to 23.50‰ and −4.68 to −5.31‰, respectively. The retrograde stage was formed from low–high-salinity (2.9 to 45.4 wt% NaCl eq.) and low–high-temperature (167 to 459 °C) fluids. The δ18O and δ13C of skarn calcites ranged from 4.34 to 15.86‰ and −3.57 to 0.23‰, respectively. The quartz-calcite-pyrite stage was formed from low-salinity (3.1–7.5 wt% NaCl eq.) and temperature (171–392 °C) fluids. The δ18O and δ13C values were −2.38‰ and 2.43‰, respectively. The quartz-carbonate stage formed from low-salinity (3.6 to 5.7 wt% NaCl eq.) and temperature (129 to 169 °C). In all phases, the eutectic and clathrate melting temperatures ranged from −59.5 to −52.2 °C and +4.4 to +12.0 °C, respectively. This indicates that the solutions contain H2O–NaCl–CaCl2–(±MgCl2)–CO2.These fluid inclusion data suggest that fluid boiling occurred under pressures between ~60 and 70 MPa based on hydrostatic consideration during the prograde stage. The main magnetite deposition occurred following boiling, with rising salinity and temperature magmatic–hydrothermal fluids and in the pressure range of ~15 to 50 MPa. Depletion in δ13C was attributed to high-temperature fluid infiltration and indicates an open-system volatilization process. It is suggested that the retrograde stage had developed in two episodes, with the carbofracturing effect triggered by CO2. The carbon isotope data of calcites indicate the mixing of low-temperature metasomatic and meteoric water in later stages. The mineralogy, microthermometry, and carbon isotope results reveal that Kaman iron deposits were developed by a combination of processes such as contact infiltration metasomatism, fluid–rock interaction, cooling, and fluid mixing as a result of decreasing pressure.

Reduction of well stimulation period after hydraulic fracturing

This article discusses the problems associated with the removal of proppant, mechanical particles of the rock and undecomposed fluid from the hydraulic fracture into the well. The necessity of developing a device for washing the perforation interval has been identified and justified. It is shown that hardened and viscoelastic gel particles fall into perforations and adhere to the walls of channels and wells. Subsequently, these zones of gel deposition reduce permeability in perforation channels. The author has developed the design of a device for decolmation (declogging), which reduces the time for well development after hydraulic fracturing. To increase the productivity of the considered wells, it is necessary to flush them with the presented device in the mode of maximum approximation to deposits. To carry particles better to the surface, it is proposed to use foam systems generated by the jet pump, which is described in this article.

Vosnesensky Cu-porphyry deposit (Southern Urals): formation conditions, trace elements, sulfur isotopes and fluid sources

The paper shows new fluid inclusion and isotopic-geochemical data for minerals from sulphide-carbonate-quartz veins of Vosnesensky Cu-porphyry deposit. Fluid inclusions were analyzed by means Linkam TMS-600 cryostage equipped with Olympus BX 51 optical microscope; trace element amounts were performed used Agilent 7700x and ELAN 9000 mass-spectrometers; sulphur isotopic composition was analyzed on DeltaPLUS Advantagе mass-spectrometer. We determined that fluid inclusions in quartz were homogenized between 215 and 315 ºС, and in latest calcite, they are 230–280 ºС. Fluids are К-Na water chloride with salinity of 3–12 wt % NaCl-eq. Quartz contain high amounts of Al (184–5180 ppm), K (20.1–1040 ppm), Na (30.2–1570 ppm) and Ti (38.4–193 ppm). The REE distribution spectra of pyrite are characterized by light lanthanides accumulation (LaN/YbN = 3.6–6.44), and negative of Ce anomalies (0.7–0.92) and Eu (0.78–0.99). The Y/ Ho ratio in pyrite varies from 27.6 up to 36.8. The δ34S values in pyrite were –1.01…0.8 ‰, in chalcopyrite – 0.9 ‰. The data testify the Cu-porphyry mineralization of Vosnesensky deposit was formed due to magmatic acid high-aluminous К-Na chloride fluid enriched with light REE in mesothermal environment. We identified the geochemical markers of interaction between fluid and host rocks.

The Morro Vermelho hypogenic karst system (Brazil): Stratigraphy, fractures, and flow in a carbonate strike-slip fault zone with implications for carbonate reservoirs

The Morro Vermelho Cave (MVC) (Brazil) developed within the Morro Vermelho karst system, which affected Neoproterozoic limestones (Salitre Formation). The MVC experienced little interactions with meteoric processes and is an example of a hypogenic cave formed during strike-slip deformation. The Salitre carbonates in the MVC experienced distributed deformation along an elongated domain overlying a buried strike-slip fault. Gently dipping, semiductile shear zones formed with decimeter-scale (3.9 in.) dolomitic veins. In our model, Mg-rich fluids flowing along the Salitre aquifer caused at the same time extensive dolomitization of the body of rock (100-m [328-ft] scale) experiencing distributed deformation. With progressive displacement, the deep strike-slip fault propagated upward causing the development of an anticline pop-up, steepening sedimentary layers, and steep 1–10-m-long (3.3–33.8-ft) fractures, which served as pathways for upward fluid flow. These steep extensional fractures made it possible for fluids flowing in lower, quartzitic aquifers to enter the carbonate aquifer causing silica deposition in rock cavities and in fractures and fault planes. Following the main stage of speleogenesis, silica deposition took over again depositing on the cave walls a continuous silica crust, rarely observed in other settings worldwide. The interplay between regional bedding-parallel flow and focused circulation of fluids along steep faults and dipping layers, and the associated rock–fluid interactions are not unique to the contractional settings presented but can also occur in association with similar faults in rifted continental margins.

Predictive Modeling of Relative Permeability Using a Generalized Equation of State

Summary Reliable simulation of enhanced oil recovery (EOR) processes depends on an accurate description of fluid transport in the subsurface. Current empirical transport models of rock-fluid interactions are fit to limited experimental data for specific rock types, fluids, and boundary conditions. In this paper, a general equation-of-state (EoS) approach is developed for relative permeability (kr) based on a set of geometric state parameters: normalized Euler characteristic (connectivity) and saturation. Literature data and pore network modeling (PNM) simulations are used to examine the functional form of the EoS. Our results show that the new kr-EoS matches experimental data better than the conventional Corey form, especially for highly nonlinear relative permeabilities at low saturations. Using hundreds of PNM simulations, relative permeability scanning curves show a locus of residual saturation and connectivity that defines an important limit for the physical kr region. The change of this locus is also considered for two contact angles. PNM data further allow for the estimation of the relative permeability partial derivatives that are used as inputs in the EoS. Linear functions of these partials in the connectivity-saturation space renders a quadratic response of kr, which shows excellent predictions. Unlike current empirical models that are based on only one residual saturation, the state function approach allows for dynamic residual conditions critical for capturing hysteresis in relative permeability.

Novel Insights into the Pore-Scale Mechanism of Low Salinity Water Injection and the Improvements on Oil Recovery

The long-held industry view that the Low Salinity Effect (LSE) depends mainly on rock–fluid interactions has led to failures and successes that can be explained by fluid–fluid interactions. Therefo...

Role of Preexisting Rock Discontinuities in Fracturing Fluid Leakoff and Flowback

During hydraulic fracturing, thousands of barrels of fluid are injected into the rock surrounding the created fractures. Observations show that later during flowback, only a small fraction of the injected fluid volume is produced back. In tight naturally fractured formations, this can be explained by the leading role of preexisting rock discontinuities in the transport of fluids in such rocks. In this work, we investigate the mechanics of injected fluid flow in and out of preexisting rock discontinuities during a typical operational sequence of fracturing treatment, well shut-in and flowback. The mechanics of fluid flow in compliant discontinuities, where conductivity is sensitive to stress changes, is different from that in a stiff rock matrix. To understand and quantify rock pressurization, fluid leakoff and flowback rates, we develop a numerical model of fluid flow in a system of arbitrarily oriented discontinuities. Using this model, we predict spatial distribution of the injected fluid in a naturally fractured rock at any time after the beginning of the fracturing treatment as well as after the well shut-in and during flowback. The model explains the trapping of injected fluid in the discontinuities during production. We validate the model by comparison with field data and provide rough estimates of the volumetric fracturing fluid accumulation in the rock discontinuities after the treatment. The spatial extent of rock “flooding” around hydraulic fractures is found to depend on the density and orientation of rock discontinuities.

A monolithic coupled hydraulic fracture model with proppant transport

This article presents the first monolithic coupled numerical model for simulating proppant transport through a non-planar propagating hydraulic fracture. A fracture is propagated through a two-dimensional domain, driven by the flow of a proppant-laden slurry. Modeling of the slurry flow includes the effects of proppant bridging and the subsequent flow of fracturing fluid through the packed proppant. This allows for simulation of a tip screen-out, a phenomenon in which there is a high degree of physical interaction between the rock deformation, fluid flow, and proppant transport and leads to shock formation in the solution.The numerical implementation is verified and the model is used to simulate a tip screen-out in both planar and non-planar fractures. An analysis of the results is performed for three different coupling schemes: monolithic, sequential, and loose coupling. The monolithic scheme is shown to be optimal in terms of computational efficiency, robustness, and accuracy. In addition, a robust and more efficient algorithm for injection-rate controlled hydraulic fracturing simulation based on global mass conservation is presented in this article.

Numerical simulation of stress shadow in multiple cluster hydraulic fracturing in horizontal wells based on lattice modelling

Multiple cluster hydraulic fracturing is widely used in the development of shale reservoir. The morphology of multiple fractures propagating from multiple cluster is complex due to the stress shadow effect. The design and operation of multiple cluster hydraulic fracturing in horizontal wells require adequate knowledge of the effect of different factors, including rock properties, in-situ stresses and fluid properties on the fracture morphology. In this paper, lattice simulation, a new particle based computational method was used to investigate the multiple cluster hydraulic fracturing in shale. The results showed that stress anisotropy and cluster spacing play an important role on geometry of the propagating fracture. The middle hydraulic fracture is restricted to propagate when cluster spacing is decreased. Simultaneous, two-step and sequential fracturing scenarios in a single horizontal well were simulated. The simultaneous and sequential fracturing showed to mainly affect the fracture propagation morphology with little effect on fracture length, while the middle fracture is shorter than its two side fractures in two-step fracturing. In two horizontal models, the simultaneous and sequential fractures showed similar morphology during multiple cluster hydraulic fracturing. In term of stimulated reservoir volume (SRV), zipper fracturing showed the largest SRV during multiple cluster hydraulic fracturing in two horizontal wells.

Seismic AVO statistical inversion incorporating poroelasticity

Seismic amplitude variation with offset (AVO) inversion is an important approach for quantitative prediction of rock elasticity, lithology and fluid properties. With Biot–Gassmann’s poroelasticity, an improved statistical AVO inversion approach is proposed. To distinguish the influence of rock porosity and pore fluid modulus on AVO reflection coefficients, the AVO equation of reflection coefficients parameterized by porosity, rock-matrix moduli, density and fluid modulus is initially derived from Gassmann equation and critical porosity model. From the analysis of the influences of model parameters on the proposed AVO equation, rock porosity has the greatest influences, followed by rock-matrix moduli and density, and fluid modulus has the least influences among these model parameters. Furthermore, a statistical AVO stepwise inversion method is implemented to the simultaneous estimation of rock porosity, rock-matrix modulus, density and fluid modulus. Besides, the Laplace probability model and differential evolution, Markov chain Monte Carlo algorithm is utilized for the stochastic simulation within Bayesian framework. Models and field data examples demonstrate that the simultaneous optimizations of multiple Markov chains can achieve the efficient simulation of the posterior probability density distribution of model parameters, which is helpful for the uncertainty analysis of the inversion and sets a theoretical fundament for reservoir characterization and fluid discrimination.

The influence of fluid type on elastic wave velocity and attenuation in volcanic rocks

Volcano-seismic signatures are the convolution of source and path effects. The source signature provides important information about the dynamic rock deformation and fluid resonance processes within the volcano, but path effects are the result of the volcanic plumbing, the edifice physical conditions, and the complex geological structure. Complicating the inversion of seismic data further, is the influence of fluid properties. Here, we use ultrasonic experiments to understand the effect of variable fluid viscosity and bulk modulus on P-wave attenuation and velocity for volcanic rocks from White Island volcano (Whakaari), New Zealand.Our experimental conditions for high-porosity ash tuff and low-porosity lava resemble shallow and deep volcano facies respectively. P-wave velocity, Vp, and quality factor, Qp, increase with the viscosity and bulk modulus of the saturating fluid and decrease with porosity and fracture volume. Tuffs are highly sensitive to saturating fluid, with variations in Vp of up to 67% and Qp of 383%. Vp and Qp in fractured lavas are slightly less sensitive to fluids (24% and 296% respectively), but Vp can be used to identify lithology for these tuff vs. lavas. Comparison of the experimental data with rock physics models suggests that squirt flow is the dominant attenuation mechanism for viscosities greater than that of water, while scattering losses may be important in gas saturated rocks. Our results have significant implications for the interpretation of seismic tomography studies and for volcano hazard monitoring based on the characteristics of detected seismicity.

Experimental investigation of phase relations in the system NaAlSi3O8–H2O at high temperatures and pressures: liquidus relations, liquid–vapor mixing, and critical phenomena at deep crust–upper mantle conditions

Supercritical fluids in rock–H2O systems have been proposed to be important agents of mass transfer in subduction zone environments. New experimental studies were conducted on the simple model granite system NaAlSi3O8 (Ab)–H2O in order to investigate phase relations and to develop the thermodynamic mixing properties between aqueous fluid (a.k.a. vapor, V) and silicate melt (a.k.a. liquid, L) at pressures (P) and temperatures (T) approaching those of critical mixing. We established liquidus and solvus phase relations by analyzing the quenched run products from piston–cylinder experiments over a range of $$P - T - X_{{{\text{H}}_{2} {\text{O}}}}$$ conditions from 1.0 to 1.7 GPa, 630–1060 °C and 4–92 wt% H2O. Equations for the critical curve, solidus temperatures, albite solubility at the solidus, and vapor-saturated solidus H2O content were formulated as functions of $$P - T - X_{{{\text{H}}_{2} {\text{O}}}}$$ . We constructed a subregular solution model to describe the solvus curves using P and T dependent Margules coefficients ( $$W_{{{\text{H}}_{2} {\text{O}}}}$$ and $$W_{\text{Ab}}$$ ). Activities of H2O and Ab ( $$a_{{{\text{H}}_{2} {\text{O}}}}$$ and $$a_{\text{Ab}}$$ ) could be formulated using only the input at the solidus and the critical point at each pressure because of the nearly linear dependence of the parameters on T. The solvus curves were confirmed independently by means of criteria established for classification of quenched products as L, L + V, or V and are in excellent agreement with the compositions that can be calculated using the Margules coefficients. At 1.6 GPa, the H2O content at the vapor-saturated solidus is 44.5 ± 5.5 wt% and the solubility of albite at the solidus is 42.95 ± 0.99 wt%, indicating the imminent intersection of the two curves and thus a stable critical endpoint at some slightly higher pressure. We constrain the critical endpoint at 1.63 ± 0.02 GPa, 659 ± 5 °C, and a composition of ~ 44.7 wt% H2O based on the intersections of the pressure dependent solidus curves with the critical curve, the pressure dependent albite solubility curve with the vapor-saturated solidus curve. The 1.7 GPa experiments showed no evidence for liquid–vapor immiscibility across a wide range of compositions and temperatures (4–80 wt% H2O and 630–1050 °C, and furthermore, that low albite is stable in the presence of the supercritical fluid near the breakdown of albite to jadeite and quartz. These results provide a comprehensive account of the solution properties of subcritical and supercritical fluids in this model granite system at temperatures and pressures corresponding to the deep-crust regions of granite magma generation.

Basin inversion and structural architecture as constraints on fluid flow and Pb–Zn mineralization in the Paleo–Mesoproterozoic sedimentary sequences of northern Australia

Abstract. As host to several world-class sediment-hosted Pb–Zn deposits and unknown quantities of conventional and unconventional gas, the variably inverted 1730–1640 Ma Calvert and 1640–1575 Ma Isa superbasins of northern Australia have been the subject of numerous seismic reflection studies with a view to better understanding basin architecture and fluid migration pathways. These studies reveal a structural architecture common to inverted sedimentary basins the world over, including much younger examples known to be prospective for oil and gas in the North Sea and elsewhere, with which they might be usefully compared. Such comparisons lend themselves to suggestions that the mineral and petroleum systems in Paleo–Mesoproterozoic northern Australia may have spatially, if not temporally overlapped and shared a common tectonic driver, consistent with the observation that basinal sequences hosting Pb–Zn mineralization in northern Australia are bituminous or abnormally enriched in hydrocarbons. Sediment-hosted Pb–Zn mineralization coeval with basin inversion first occurred during the 1650–1640 Ma Riversleigh Tectonic Event towards the close of the Calvert Superbasin with further pulses taking place during and subsequent to the onset of the 1620–1580 Ma Isa Orogeny and final closure of the Isa Superbasin. Mineralization is typically hosted by the post-rift or syn-inversion fraction of basin fill, contrary to existing interpretations of Pb–Zn ore genesis where the ore-forming fluids are introduced during the rifting or syn-extensional phase of basin development. Mineralizing fluids were instead expelled upwards during times of crustal shortening into structural and/or chemical traps developing in the hangingwalls of inverted normal faults. Inverted normal faults predominantly strike NNW and ENE, giving rise to a complex architecture of compartmentalized sub-basins whose individual uplifted basement blocks and doubly plunging periclinal folds exerted a strong control not only on the distribution and preservation of potential trap rocks but the direction of fluid flow, culminating in the co-location and trapping of mineralizing and hydrocarbon fluids in the same carbonaceous rocks. An important case study is the 1575 Ma Century Pb–Zn deposit where the carbonaceous host rocks served as both a reductant and basin seal during the influx of more oxidized mineralizing fluids, forcing the latter to give up their Pb and Zn metal. A transpressive tectonic regime in which basin inversion and mineralization were paired to folding, uplift, and erosion during arc–continent or continent–continent collision, and accompanied by orogen-parallel extensional collapse and strike-slip faulting best accounts for the observed relationships.

Formation conditions, composition and ore-forming sources of the Bolshoy Karan gold-porphyry deposit (the Southern Urals)

Research subject. We studied PT conditions, composition and sources of ore-forming fluids of the Bolshoy Karan goldporphyry deposit (South Urals) confined to the Main Urals Fault zone at Southern Urals. Methods. Temperatures of ore mineral formation, salt composition and fluid salinity were estimated using a Linkam TMS-600 cryostage equipped with an Olympus BX 51 optical microscope. The gas composition of fluid inclusions was determined using a Horiba LabRam HR800 Evolution Raman spectrometer and an Olympus BX-FM optical microscope. Trace elements were detected by means of LA-ICP-MS analysis. С and О isotopic composition was identified using a MAT 253 (Thermo Fisher Scientific) mass-spectrometer. S in the minerals of sulphide-carbonate-quartz ores was identified using a Delta PLUS Advantage mass-spectrometer. Results. It is shown that the fluid inclusions in quartz are homogenized at 370–310oC, while those of the latest calcite – at 234–200oС. The fluids contain Mg-Na chloride solutions with a salinity of 3.0–11.9 wt % NaClэкв. According to LA-ICP-MS data, quartz contains high Al contents (916–1556 ppm) confirming its formation from a high aluminous acid fluid. The REE distribution spectra in calcite are characterized by the accumulation of light lanthanides (La N /Yb N = 3.4–9.11) pointing to the acid fluid composition, as well as by negative Ce (0.58–0.88) and positive Eu (1.51–3.61) anomalies. The negative Ce anomaly may have been caused by interactions between the fluid and host limestones. The positive Eu anomaly reflects the existence of a middle-temperature environment (>250oC) prior to calcite crystallization. Y/Ho values in calcite (29.3–35.6) suggest the presence of magmatic components and those extracted from limestones. The values of δ 18 О in calcite vary from 14.7 to 19.8‰, while those of δ 13 С – from –4.1 to 0.7‰. The values of δ 18 О H 2 O for the ore-forming fluid, which were calculated based on average homogenization temperatures of fluid inclusions in calcite (230oС), vary from 6.5 to 11.5‰, while δ 13 С СO 2 – from –3.21 to 1.6‰. δ 34 S values in pyrite ranged from –0.60 to – 1.50‰. Conclusions. Our data confirm the formation of the gold-porphyry mineralization of the Bolshoy Karan deposit under mesothermal conditions. Magmatic fluids played the key ore-formation role. The geochemical peculiarities of interactions between the fluid and host rocks were revealed.

Koyna earthquakes: a review of the mechanisms of reservoir-triggered seismicity and slip tendency analysis of subsurface faults

Koyna region in western India experienced more than 1,00,000 earthquakes of different magnitudes (M ~ 1.0–6.3) in the past five decades. Earthquakes in this region are believed to be triggered by a change in fluid pressure due to the percolation of the reservoir (Koyna and Warna reservoir) water into the subsurface. A drilling program was set up by the Ministry of Earth Sciences, India and International Continental Scientific Drilling Program (ICDP) to study the deep subsurface lithology, structure, thermal attributes, etc. as the area is covered by ~ 950 m of thick Deccan basalts. This paper reviews all the hypotheses proposed by earlier workers to explain the mechanism of reservoir trigger causing earthquakes and summarizes such theories to a simple generic model. Slip tendency analysis was further carried out based on the proposed model to explain the dependence of fault slip on fault geometry, rock mechanical properties, stress and fluid gradients. Finally, faults at various depths were characterized (favourably oriented, unfavourably oriented and severely misoriented) based on their potential to go into failure.

Stochastic inversion method of time-lapse controlled source electromagnetic data for CO2 plume monitoring

Carbon dioxide storage in deep saline aquifers can potentially reduce the CO2 concentration in the atmosphere due to anthropogenic activities with limited environmental impact. To minimize the risks of leakage, it is necessary to monitor the CO2 distribution in the reservoir. Here, we present a stochastic optimization method namely the Ensemble Smoother, to invert time-lapse marine controlled source electromagnetic data for predicting the CO2 plume location. Electromagnetic surveys have been successfully used in subsurface monitoring studies in different geosciences applications due to their sensitivity to the changes in the fluid in porous rocks. The inverse method is based on a Bayesian approach, in which an ensemble of stochastically generated prior models representing the spatial distribution of CO2 saturation is updated according to the mismatch between the measured data and the predicted electromagnetic response of the prior models. The proposed method generates an ensemble of updated realizations, the posterior models of the spatial distribution of CO2 saturation, that match the observations. The variance of the posterior models represents the uncertainty of the CO2 distribution. Compared to deterministic inversion methods, our proposed method is better suited to solve non-linear inverse problems with the added benefit of uncertainty quantification. The method is tested and validated on a real dataset, the Johansen formation, offshore Norway, for which we created synthetic time-lapse electromagnetic data for the entire injection period. The inversion of electromagnetic data shows that the proposed method can accurately predict the prediction of the CO2 plume location and quantify the associated uncertainty.

Can Effects of Temperature on Two-Phase Gas/Oil-Relative Permeabilities in Porous Media Be Ignored? A Critical Analysis

Thermal recovery processes for heavy oil exploitation involve three-phase flow at elevated temperatures. The mathematical modeling of such processes necessitates the account of changes in the rock–fluid system’s flow behavior as the temperature rises. To this end, numerous studies on effects of the temperature on relative permeabilities have been reported in the literature. Compared to studies on the temperature effects on oil/water-relative permeabilities, studies (and hence, data) on gas/oil-relative permeabilities are limited. However, the role of temperature on both gas/oil and oil/water-relative permeabilities has been a topic of much discussion, contradiction and debate. The jury is still out, without a consensus, with several contradictory hypotheses, even for the limited number of studies on gas/oil-relative permeabilities. This study presents a critical analysis of studies on gas/oil-relative permeabilities as reported in the literature, and puts forward an undeniable argument that the temperature does indeed impact gas/oil-relative permeabilities and the other fluid–fluid properties contributing to flow in the reservoir, particularly in a thermal recovery process. It further concludes that such thermal effects on relative permeabilities must be accounted for, properly and adequately, in reservoir simulation studies using numerical models. The paper presents a review of most cited studies since the 1940s and identifies the possible primary causes that contribute to contradictory results among them, such as differences in experimental methodologies, experimental difficulties in flow data acquisition, impact of flow instabilities during flooding, and the differences in the specific impact of temperature on different rock–fluid systems. We first examined the experimental techniques used in measurements of oil/gas-relative permeabilities and identified the challenges involved in obtaining reliable results. Then, the effect of temperature on other rock–fluid properties that may affect the relative permeability was examined. Finally, we assessed the effect of temperature on parameters that characterized the two-phase oil/gas-relative permeability data, including the irreducible water saturation, residual oil saturation and critical gas saturation. Through this critical review of the existing literature on the effect of temperature on gas/oil-relative permeabilities, we conclude that it is an important area that suffers profoundly from a lack of a comprehensive understanding of the degree and extent of how the temperature affects relative permeabilities in thermal recovery processes, and therefore, it is an area that needs further focused research to address various contradictory hypotheses and to describe the flow in the reservoir more reliably.

Characteristics of surface hydrothermal alteration around Gunung Pancar area, West Java, Indonesia

Hydrothermal alteration is an interaction between rock and hydrothermal fluid by means changing the mineralogical composition of the rock. This process is controlled by permeability, chemical composition, temperature, pressure, and duration of the hydrothermal alteration. Gunung Pancar, located in West Java, is considered an outflow for Gunung Gede Geothermal System. Typical geothermal surface manifestations found around Gunung Pancar are hot springs, warm ground and surface alteration. Basic geological mapping was conducted followed by water and altered rock sampling. Petrographic and diffraction methods are completed to confirm altered protolith. Water analyses were conducted to determine water type and origin. Alteration zonation is then inferred based on the water type, intensity of alteration and then cross referenced with indication of structural geological features. Zonation reveals that the intensity of alteration gets weaker as it moves away from the apparent faults. The result suggested that the permeability of the host rock affects thermal fluid movement around Gunung Pancar and subsequently the local geothermal conceptual model.