Reservoir Temperature Research Articles

Fluid flow in crustal fault zones with varying lengthwise thickness: application to the Margeride fault zone (French Massif Central)

Crustal fault zones, holding promise as potential geothermal reservoirs, remain largely untapped and unexplored. Located in the southern Massif Central, France, the Margeride fault zone (MFZ) varies in thickness (lateral extension perpendicular to the fault plane) from 100 m to over 2500 m. Reactivated several times under different stress regimes since the Variscan orogeny, this zone is characterized by an intense alteration and fracturing. As a result, the multiple reactivation of the fault zone has maintained permeability, leading to favourable conditions for fluid circulation. Structural measurements and geological cross sections were used to precisely constrain thickness and geometry of the fault zone. North of the MFZ, the Coren thermal spring indicates reservoir temperatures of about 200–250 °C, hinting at the possible existence of a temperature anomaly. To investigate this geothermal potential, 3D numerical models simulating fluid circulation within a fault zone were conducted. Various configurations were explored, altering fault zone thickness and permeability for two key geometries. The first geometry, which manipulated the width of the fault zone along its length, demonstrated a direct correlation between fault zone thickness and amplitude of thermal anomaly. Thinner faults (< 500 m) exhibited multiple weak positive thermal anomalies, while thicker faults (> 500 m) tended to develop a single, substantial positive thermal anomaly. In the second examined geometry, where fault zone thickness increased longitudinally, a consistent positive temperature anomaly emerged at the thickest section of the fault zone. Depending on the permeability value, an additional anomaly may develop but will migrate laterally towards the thinnest part of the fault zone. This multi-disciplinary approach, combining numerical modelling and field measurements, presents a predictive methodology applicable to geothermal exploration in analogous basement domains. In our case, it has shown that the northern end of the Margeride fault zone could represent an area that needs to be explored further to assert its high geothermal potential. Our numerical models will increase understanding of how fault width and geometry impact the geothermal potential of the Margeride fault zone and similar areas in crystalline basement.

Numerical Simulation of Gas–Liquid–Solid Erosive Wear in Gas Storage Columns

Gas reservoirs play an increasingly important role in oil and gas consumption and safety in China. To study the problem of erosion and wear caused by gas-carrying particles in the process of gas extraction from gas storage reservoirs, a mathematical model of gas–liquid–solid three-phase erosion of gas storage reservoir columns was established through theories of multiphase flow and particle motion. Based on this model, the effects of the water volume fraction, gas extraction rate, particle mass flow rate, particle size, and bending angle on the erosion location and rate of the pipe columns were investigated. The findings indicate that when the water content volume fraction is low, the water production volume minimally affects the maximum erosion rate of pipe columns. Conversely, the gas extraction rate exerted the most significant influence on the column erosion, showing a power function relationship between the two. When gas extraction volume exceeds 60 × 104 m3/d, the maximum erosion rate surpasses the critical erosion rate of 0.076 mm/a. This coincided with the increased sand mass flow rate, although the maximum erosion rate of the pipe columns remained relatively steady. The salt mass flow rate demonstrated a linear relationship with the erosion rate, with the maximum erosion rate exceeding the critical erosion rate of 0.076 mm/a. The maximum erosion rate of the pipe columns increased, stabilized with larger sand and salt particle sizes, and exhibited an increasing trend with the bending angle. For gas extraction volumes exceeding 46.4 × 104 m3/d and salt mass flow rates exceeding 22 kg/d, the maximum erosion rate of pipe columns exceeds the critical erosion rate of 0.076 mm/a. The conclusions of this study are of some importance for the clarification of the influencing law of pipe column erosion under high temperature and high pressure in gas storage reservoirs and for the formulation of measures for the prevention and control of pipe column erosion in gas storage reservoirs.

Subsea Capping-Stack Usage Evaluated for CO2 Blowouts

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 35246, “Evaluating Subsea Capping-Stack Usage for CO2 Blowouts,” by Lei Zhou, SPE, SLB, Eric R. Upchurch, SPE, Chevron, and Yaxin Liu, SPE, SLB, et al. The paper has not been peer reviewed. _ A dynamic multiphase-flow simulator was used to investigate a capping operation for CO2 well blowouts. Following the typical sequence of a capping procedure and applying a soft shut-in, different primary bore sizes and choke-line configurations were considered. Additionally, different reservoir flow rates, fluid types [CO2 and methane (CH4)] and water depths were investigated, with the intention of understanding what differentiates a CO2 blowout from that of CH4 under varying conditions. Introduction In offshore CO2 storage operations targeting saline aquifers, the depth and pressure gradient of such storage zones dictate that stored CO2 will almost always be in a supercritical state. Given that reality, the complexities of supercritical-to-gaseous phase transition, varying compressibilities (of both gas and supercritical fluid), and the formation of hydrates all must be addressed accurately in simulation if a path to using capping stacks in response to subsea CO2 blowouts is to be charted. Blowouts with CO2 have complications that CH4 blowouts may not exhibit, given the phase change of supercritical CO2 with significant volume expansion. Capping stacks have been the oil and gas industry’s chosen first line of response to subsea blowouts. The adaptation of subsea capping stacks for halting CO2 blowouts is a logical next step for their application. The unique properties of CO2, combined with conditions of the subsea environment, however, can lead to the formation of CO2 hydrates, frozen sea water, and dry ice. Thus, a thorough assessment of the design, deployment, and operation of capping stacks in a CO2 environment is required to ensure their effectiveness. To the authors’ knowledge, no analogous well-control modeling or case studies are available in the literature. Capping-Stack Configurations In this study, the authors consider multiple capping stacks with dimensions and ratings summarized as follows: - Stack 1: 18.75 in., two rams, pressure rating of 15,000 psi, temperature rating of 250°F, four chokes, choke inner diameter (ID) of 5.125 in. - Stack 2: 18.75 in., three rams, pressure rating of 15,000 psi, temperature rating of 250°F, two chokes, choke ID of 3.063 in. - Stack 3: 7.063 in., two gate valves, pressure rating of 10,000 psi, temperature rating of 302°F, four chokes, choke ID of 5.125 in. Well and Reservoir Scenarios Fig. 1 shows the well and reservoir scenarios used in this evaluation. The configuration in Fig. 1a is used for shallow water (984 ft), while that in Fig. 1b is used for deep water (2,500 ft). In shallow water, reservoir and mudline temperatures were assumed to be 210 and 59°F, respectively, and reservoir pressure was set at 5,000 psi. In deep water, reservoir and mudline temperatures of 167 and 40°F, respectively, were used and reservoir pressure was set at 5,500 psi. By using these static variables and varying reservoir permeability, various blowout rates were simulated ranging from 150 to 370 MMscf/D. Each scenario’s steady-state blowout condition was used as the starting point for modeling the operational steps that led to full closure of the capping stack’s primary bore and choke lines. For simulation simplicity, it was assumed that the well unloaded and stabilized with the capping stack already installed on the well. This assumption had no effect on the final simulation results that reflected how fluid behaved during the process of shutting in the well.

Hydrochemical Characterisation and Genesis Mechanism of Li‐Rich Geothermal Waters in the High‐Temperature Geothermal Areas of Western Sichuan, China

ABSTRACTLithium (Li) is a valuable resource with significant economic benefits and strategic importance. The extraction of Li from Li‐rich geothermal fluids has low production costs and may be an essential source of Li in the future. The Li contents in the high‐temperature geothermal systems of western Sichuan are high (most exceeding 1 mg/L) and reach the exploration standard. However, the Li source and enrichment processes of high‐temperature geothermal fluids are not well known. Therefore, 30 groups of natural hot springs with Li ≥ 1 mg/L from Batang, Litang, and Kangding high‐temperature geothermal systems were selected to analyse the Li enrichment mechanism in high‐temperature geothermal water. The average exposed temperatures of Batang, Litang, and Kangding geothermal waters were 82.4°C, 53.7°C, and 61.9°C, respectively, and the hydrochemical types were HCO3‐Na. The average concentrations of Li in the geothermal waters of Batang, Litang, and Kangding were 2.32, 3.29, and 3.54 mg/L. Based on the δD and δ18O characteristics, the geothermal waters in the study area originated from meteoric water and snow‐melt water. Magmatic water was also mixed during circulation, with Kangding geothermal water being the most mixed (25.0%). Strong water–rock interactions occurred during geothermal water runoff ascent, including silicate mineral dissolution, geothermal gas dissolution, and cation exchange. The deep reservoir temperatures in the geothermal systems of Batang, Litang, and Kangding were estimated to be 239°C, 200°C, and 242°C, and the shallow reservoir temperatures were 175°C, 86°C, and 116°C. Finally, two Li enrichment mechanisms were proposed: (1) Li in the geothermal waters of Batang and Litang geothermal systems mainly came from the leaching of lepidolite and spodumene during water–rock interactions. (2) Li in the Kangding geothermal system mainly originated from the input of magmatic water. This research deepens the understanding of Li enrichment mechanisms in high‐temperature geothermal systems, which will be helpful for the exploration of geothermal Li resources.

Learning with computer simulations: a case study on reservoir temperatures in carnot cycles

Computer simulations have played a significant role in the development of physics, and in physics education as well. Researchers have addressed whether simulations promote learning, but few studies have investigated how simulations actually participate in learning processes. This study seeks to describe how simulations participate in conceptual learning. A case study is carried out using videotaped interviews with three groups of undergraduate students as they address a problem-solving task on thermodynamics (Carnot cycles). Students use a specifically developed simulation for support. The analysis is based on Coordination Class Theory (CCT). Results indicate that students not only use the simulation to think; it is actually a part of what they think. Students were found to engage in three different interaction dynamics with the simulation. Attuned with CCT, these were coded as either Extractive/Inferential/Articulative interactions. In each case, the substance of how these interactions input conceptual learning is described. Implications for future research and for teaching are given.

Production Performance Analysis to Mature Field Development Plan

The research focuses on evaluating the production performance of three oil wells-Well F55A MB, Well Hovea 13 ST1, and Well Pedirka-1-using Inflow Performance Relationship (IPR) and Vertical Lift Performance (VLP) analysis to determine optimal artificial lift methods for each case. The study explores critical production parameters such as reservoir pressure, temperature, and gas-to-oil ratio (GOR) while employing decision tree methodologies to select suitable artificial lift systems. For Well Hovea 13 ST1 and Well Pedirka-1, gas lift installations significantly enhanced oil recovery rates by optimizing injection pressures and valve placements, achieving production gains of 694 and 300 barrels per day, respectively. In contrast, Well F55A MB, characterized by high water cut and lower reservoir temperatures, was deemed unsuitable for artificial lift based on the decision tree analysis, with a stable production of 2832 stb/d. This work highlights the importance of tailored artificial lift strategies for maximizing oil recovery and improving well performance in diverse reservoir conditions.

Novel approach for modelling low enthalpy geothermal in deep sedimentary aquifers: a case study of 40 years of production data in the Dogger formation

Geothermal energy in the Paris urban area has been exploited since the early 1970s. Deep drilling in the Paris sedimentary basin has targeted hot brine in the Dogger formations from a mid-Jurassic carbonate rocks series. More than a hundred wells have been drilled to depths ranging from 1400 to 2000 m and decades of production and reinjection have resulted in variations in the aquifer pressure and temperature in some areas. The regional numerical model discussed herein is aimed at assessing the potential interactions between doublets and for assessing the impact of the addition of more wells in the future. While the integration of a 3D refined geological model into a large-scale reservoir model needs heavy computational resources, local models simplifying the main productive areas into one or two layers surrounded by impermeable units can be used to approximately assess the reservoir characteristics. The modelling of a semi-regional area of the Dogger reservoir in the Southern part of Paris (Cachan/Orly) has been performed, using a conventional double-layer approach to simulate the natural state and production history of the area using the simulator Waiwera, a fast parallel open-source geothermal simulator from the University of Auckland in New-Zealand. Calibration of a natural state model, which describes the conditions before any geothermal operations, has been performed, including an analysis of the impact of boundary condition values on the ability of the model to match the data available in the public domain. The temperature and pressure distributions, instead of being based on geostatistical mapping methods have been obtained from a calibrated natural state model. The implementation of a regional lateral cross flow observed from past studies proved to be essential for matching the measured temperatures and pressures along with variations in the deep heat flux. A calibrated model has been obtained from matching the available production data with mismatches of no more than 1.5 °C. The modelling results confirm the dominance of the shallower productive zone in the aquifers and give insights into the extent of the cooler areas created by the long-term operations. Thus we have used the Dogger reservoir, with multiple data sets available, as a case study for calibrating a semi regional numerical model of a deep sedimentary aquifer used for geothermal direct-use. Our modelling study accounts for the conceptual understanding of the sedimentary aquifer with its heterogeneities and calibrates the numerical model against the measured historical data. Based on the calibrated reservoir model, the pressure and temperature responses in deep productive areas can be determined enabling operators or decision makers to test future strategies for sustainably operating the geothermal resource.

Effects of Modified Cross-Linkers on the Rheology of Water-Based Fracturing Fluids and Reservoir Water Environment

Improving the chemical structure of the cross-linker is a potential method for reducing reservoir pollution and enhancing the fracturing efficiency of shale reservoirs. In this investigation, a three-dimensional (3-D) spherical cross-linker comprising branched chains was synthesized, and the 3-D structure of the cross-linker was analyzed through scanning electron microscopy (SEM). Furthermore, we constructed a multifunctional coupled collaborative evaluation device that can be used to evaluate numerous properties associated with water-based fracturing fluids, including fluid viscosity, adsorption capacity, and water pollution. Meanwhile, the influence of varying reservoir conditions and cross-linker content on the fluid viscosity of water-based fracturing fluids and the potential for reservoir contamination has been evaluated and elucidated. The results indicated that the synthesized cross-linker exhibited a superior environmental protection of the shale reservoir and an enhanced capacity for thickening fracturing fluids in comparison to commercial cross-linkers. Moreover, cross-linker content, reservoir temperature, reservoir pressure, and fracture width can affect fluid viscosity and reservoir residual in different trends. The addition of 0.3% nano-cross-linker (Synthetic products) to a water-based fracturing fluid resulted in an apparent viscosity of 160 mPa·s at 200 °C, and the adsorption capacity and water content of the shale reservoir were only 0.22 µg/m3 and 0.05 µg/L, respectively. Additionally, an elevation in reservoir temperature resulted in a reduction in the adsorption capacity. However, the cross-linker content in groundwater underwent a notable increase, and the cross-linker residue in water increased by 0.009 µg/L. The impact of reservoir pressure on fluid viscosity and groundwater pollution potential exhibited an inverse correlation compared to that of reservoir temperature, and the above two parameters changed by +18 mPa·s and −0.012 µg/L, respectively. This investigation provides basic data support for the efficient fracturing and reservoir protection of shale reservoirs.

Predicted effect of the grand Ethiopian renaissance dam on the Epilimnion temperature in the high Aswan dam reservoir

AbstractThe Nile River is a crucial geopolitical water stream. The construction of the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile poses significant challenges for downstream countries, including Egypt. The GERD will be the largest hydroelectric power plant in Africa and the seventh in the world. This led many researchers to investigate the impacts of the dam construction on water quantity, agriculture, power generation, and the environment. This study aims to investigate some of the environmental impacts of the operation of the GERD on the High Aswan Dam (HAD) reservoir. Water level fluctuations due to the operation of the GERD will directly affect the thermodynamics of the HAD reservoir. As a result, the vertical distribution of heat will be altered assuming the incoming solar radiation will remain the same. Studies indicate that the water level in the HAD reservoir will decline by 10–27 m, due to the filling of the reservoir upstream of the GERD over the next few years. To quantify the change in temperature, the heat content for the reservoir is calculated pre‐ and post‐dam operation. Moreover, a one‐dimensional simulation model, DYnamic REservoir Simulation Model (DYRESM), was used to simulate the change in thermal stratification of the HAD reservoir pre‐ and post‐GERD operation. Results showed that the epilimnion temperature is expected to increase during summer from an average of 31.9°C pre the GERD operation to 33.7°C post the GERD operation. Consequently, this is expected to affect the ecosystem in the reservoir. The findings of this study highlight the significant environmental impacts of the GERD on HAD reservoir. To mitigate these impacts and ensure the sustainable management of water resources in the Nile River basin, it is imperative to implement comprehensive policies and strategies.

Compressor Development for CO2-Based Pumped Thermal Energy Storage (PTES) Systems

Abstract Pumped thermal energy storage (PTES) offers a cost-effective means to store electrical energy for long duration by utilizing a heat pump cycle to transfer thermal energy from a low temperature reservoir (LTR) to a high temperature reservoir (HTR). The heat pump compressor, which represents a significant driver to the cost, performance and operating characteristics of the PTES system. During charging (&amp;gt;100 MW), traditional compressor scaling charts indicate that the operating conditions needed would be best served by a multistage axial compressor. The conceptual design of a large-scale CO2 axial compressor was completed, including mean-line estimates of the compressor performance at full power conditions. At steady state, full power operation, the isentropic efficiency and mechanical efficiency of the compressor have significant impact on the cycle design and round trip efficiency of the PTES system. The results of the conceptual design were used to refine the PTES cycle design and updated operating conditions provided for further aero design optimization. An important characteristic of the PTES system is its ability to charge at variable rate, which provides significant challenges on compressor operability, especially for a compressor that will be coupled to a fixed-speed synchronous motor. Cycle studies of variable charging rate processes have been conducted, and the impact of compressor operating map characteristics explored. Based on initial modeling studies, single compressor operation can be achieved down to at least 50% of rated power, with further reductions possible depending on the characteristics of the compressor map speedlines.

Study and pilot test of in-depth conformance control based on Janus SiO2 nanoparticle emulsions-assisted inorganic gel via dual-liquid method in offshore reservoirs

Inorganic gel is one of the conformance control methods to control excess water production and extend the lifetime of oilfields. However, the inorganic gel is challenging for dual-liquid injected method and in-depth plugging performance. With the purpose of solving this issue for the application of inorganic gel in offshore oilfiled via dual-liquid method, a conformance control system based on Janus SiO2 nanoparticles (NPs) emulsion-assisted inorganic gel was proposed. In this investigation, the inorganic gel reacted with Ca2+and Mg2+ of the reservoir as ion sources, the performance of Janus SiO2 NPs and nano-emulsions was determined, and the gelation time, rheological property, and in-depth flooding performance of Janus SiO2 NPs emulsions-assisted inorganic gel system were systematically explored. The result shows that the sodium silicate concentration is determined at 0.35 wt.% based on the formation water and temperature of target reservoir. Besides, the performance of Janus SiO2 NPs is characterized by the particle size of 24 nm, which is beneficial to extend the half-life of emulsions from 7.6 h to 48 h and oil–water interfacial tension reaches 10−1∼10−2 mN/m. Also, nano-emulsions-assisted inorganic gel system can delay gelation time from 6.3 h to 29.5 h and an significant improvement in elasticity effect. Moreover, core flooding experiments were further conducted to investigate the injection capability and in-depth plugging performance. More importantly, a pilot test also provided the sufficient evidence to demonstrate the conformance control effectiveness of the Janus SiO2 NPs emulsion-assisted inorganic gel system in offshore oil field, which can be a candidate with great potentials for further field application.

Study on the Influence of Geological Parameters of CO2 Plume Geothermal Systems

At present, there are relatively few studies on the exploitation of geothermal resources in depleted high-temperature gas reservoirs with carbon dioxide (CO2) as the heat-carrying medium. Taking the high-temperature gas reservoir of the Huangliu Formation in the Yingqiong Basin as the research object, we construct an ideal thermal and storage coupling model of a CO2 plume geothermal system using COMSOL6.2 software to conduct a sensitivity analysis of geological parameters in the operation of a CO2 plume geothermal system. The simulation results show that, compared with medium- and low-temperature reservoirs, a high-temperature reservoir exhibits higher fluid temperature in the production well and a higher heat extraction rate owing to a higher initial reservoir temperature but has a shorter system operational lifetime; the influence of the thermal conductivity of a thermal reservoir on the CO2 plume geothermal system is relatively minor, being basically negligible; and the thinner the thermal reservoir is, the faster the fluid temperature in the production well decreases and the shorter the thermal breakthrough time. These findings form a basis for selecting heat extraction areas for CO2 plume geothermal systems and also provide a theoretical reference for future practical CO2 plume geothermal system projects.

Hydrogeochemical Characteristics and Genesis of Hot Springs in Da Qaidam Area, Northern Qaidam Margin of the Qaidam Basin

Hydrogeochemical research on fluids is an effective method to understand the formation mechanism, occurrence environment, and circulation process of groundwater. The groundwater sampling sites are located in the town of Dachaidan on the northeastern edge of the Tibetan Plateau, which was selected as the study object. Samples were collected from hot and cold springs and surface water in the area. This study is based on the analysis of water chemistry and isotopes, and aims (1) to discuss the chemical characteristics of groundwater in Da Qaidam, (2) to estimate the deep reservoir temperatures, recharge elevation and circulation depth of geothermal waters, and (3) to figure out the heat source beneath the geothermal area and its genetic mechanism. The result showed the following: The hydrochemical type of the hot spring is Cl·SO4-Na and Cl-Na, and the hydrochemical type of cold spring is SO4·HCO3-Na·Ca and Cl·HCO3·SO4-Ca·Na. The main source of groundwater recharge is snow and ice melt water. The recharge elevation ranges from 4666.8 m to 5755.9 m. The geothermal reservoir temperature is about 119.15–126.6 °C. Ice and snow melt water infiltrate into the high mountainous areas on the north side of Da Qaidam and circulate underground through the developed deep and large fractures. Part of the groundwater migrates upwards under the water conduction of the Da Qaidam fault fracture zone to form cold springs, while another part is heated by deep circulation and exposed to the surface in the form of medium to low temperature tectonic hot springs. The research results can provide a scientific basis for geothermal resource exploitation and utilization in Qinghai Province.

Characteristics and main controlling factors for the development of shale micro pore-fracture in Tiemulike Formation, Yining Basin

Research on the type, size, structure, and other characteristics of shale micro pore-fracture and their genesis is one of the core index for Shale gas study. Based on systematically collected shale samples from outcrop profiles and well cores, the experiments of thin-section observation, scanning electron microscopy, energy-dispersive X-ray spectroscopy, whole-rock analysis, rock–eval pyrolysis and basin simulation analysis were performed to study the micro pore-fracture characteristics and its main controlling factors for the development of shale pores in Tiemulike Formation in Yining Basin. The results show that four types of micro pore-fractures were identified: organic hydrocarbon-generating micro pores, granular dissolved micro pores, intergranular micro pores, and micro-fracture. The development of micro pores in shales is influenced by the internal material composition of the shale reservoir and external temperature conditions. The high organic carbon content with a high degree of thermal evolution led to the development of numerous micro pores, and the main micro pores were produced by shrinking the hydrocarbon generation volume due to the thermal evolution of organic matter. The development of micro-fractures was found to be favoured by the high content of brittle minerals and overpressure in the formation.

Numerical simulation–based optimization of an integrated framework for the efficient development and sustainable utilization of geothermal resources: Application to the Bedugul geothermal field

Geothermal energy is a crucial renewable resource that can generate large power continuously but requires integrated and accurate assessments of its development and utilization for long-term and sustainable exploitation. Accordingly, this study develops an assessment framework considering all the influential factors for power generation: the potential capacity; silica scaling; type of power generation system; and temporal changes in the pressure, temperature, and fluid saturation in the reservoir. The applicability and effectiveness of the proposed method are demonstrated via a case study of the Bedugul geothermal two-phase system on Bali Island, Indonesia, using a calibrated numerical model and a stochastic resource assessment. The numerical model is a combination of wellbore, silica scaling, and thermodynamic power generation models. On the basis of the wellbore model by the Hagedorn and Brown pressure drop correlation, the calculated means of the production capacity and enthalpy from the liquid reservoir are 39.0 kg/s and 1340 kJ/kg, respectively. Using double-flash and flash-binary power generation systems over an exploitation period with a two-phase reservoir temperature of 260 °C, a reinjection temperature of 130 °C, and a silica scaling model, the predicted production from the liquid reservoir can sustain a power generation of 60 MWe, which is equivalent to 70 % of the power potential, according to a stochastic resource assessment using the Plackett–Burman design. The double-flash system is found to generate 1.0 MWe more power (a 1.6 % increase relative to the baseline capacity) than the flash-binary system using pentane as working fluid and to extend the lifetime of the make-up wells by 2.5 years. Consequently, it is vital, at an early stage of development, to understand the nature and properties of reservoirs and the thermodynamics of power generation systems via comprehensive research and reliable and accurate assessments of the power production capacity.

Integrating geomechanical proxy models with data assimilation for energy transition applications

This study presents a method to address the significant uncertainties in subsurface modeling that impact the efficiency of energy transition applications such as geothermal energy extraction and CO2 geological storage. The approach combines a physics-based geomechanical proxy model with an ensemble smoother with multiple data assimilation (ES-MDA), aimed at enhancing uncertainty quantification through the integration of vertical displacement measurements from fluid production and injection. The data from wells is limited in spatial coverage, while these measurements offer extensive spatial information, improving the understanding of subsurface behavior by reflecting changes in reservoir pressure and temperature. The open-DARTS simulator for fluid flow and a geomechanical proxy are used to perform data assimilation with ES-MDA. By generating an ensemble of model realizations with varied permeability, calculating vertical displacements at the surface, and applying ES-MDA, we effectively identify the probability distribution of the vertical displacement of the model conditioned to observed subsidence data. Entropy is used as a statistical measure to quantify the reduction of uncertainty of subsurface models based on observations. Our approach was tested on a 2D conceptual and 3D realistic datasets, demonstrating its capability to provide data assimilation. This workflow represents an advancement in subsurface modeling, supporting informed decision-making in geothermal energy production and CO2 sequestration by offering an improved alternative for data assimilation and enhancing tools for uncertainty quantification.

ГЕОТЕРМИЧЕСКАЯ МОДЕЛЬ НЕФТЕГАЗОНОСНЫХ ОТЛОЖЕНИЙ ВИЛЮЙСКОЙ ГЕМИСИНЕКЛИЗЫ

The paper deals with the presented results of geothermal studies of Paleozoic and Mesozoic deposits within the Vilyuy hemisyneclise and adjacent territories. Features of geothermal zoning of oil-and-gas deposits are determined by the cryogenic stratum developed everywhere here, structural plan and heat flow magnitude. The lowest values of heat flow (up to 35 MW/m2) are typical for the western and south-western regions of the Vilyuy hemisyneclise, the largest (up to 50 MW/m2 or more) values are сharacteristic of central and eastern ones. The thickness of the cryogenic stratum naturally increases with a distance from the Lena River valley, where a through talik is developed, in a north-western direction, where it exceeds 1000 m; the thickness of the cryogenic stratum is 600–650 m in the central regions of the hemisyneclise. Two types of vertical geothermal zoning have been determined. The first type with low geothermal gradients (0.49–1.40 °C/100 m) was revealed in the southern, north-western and north-eastern margins; the second one (more than 2 °C/100 m) – throughout most of the studied region. The thermal regime of Cambrian rocks is significantly influenced by disjunctive tectonics, which is expressed in an increase in the values of current reservoir temperatures in the south-east of the research area (more than 180–190 °C).

Analisis Efesiensi Mesin Carnot Dalam Sistem Termodinamika

This study aims to analyze the literature related to the efficiency of the Carnot Engine in thermodynamic systems, focusing on theoretical limitations and factors affecting efficiency in real applications. The Carnot Engine, as an ideal model, provides an illustration of the maximum efficiency limit for the conversion of heat energy into work in a system involving two heat reservoirs at different temperatures. This ideal efficiency, which is determined only by the reservoir temperatures, is difficult to achieve in practice due to irreversibility factors such as friction, imperfect heat transfer, and entropy increase. This literature review presents a deeper understanding of the principles of thermodynamic efficiency, the applications of the Carnot cycle in modern technologies such as power generation and refrigeration systems, and the challenges in approaching ideal efficiency in real engines. The results of this analysis are expected to contribute to improving energy efficiency in various industrial sectors.

Experimental Study on Enhanced Oil Recovery of Shallow Super-Heavy Oil in the Late Stage of the Multi-Cycle Huff and Puff Process

The shallow, thin super-heavy oil reservoir demonstrates certain characteristics, such as shallow reservoir depths, low-formation temperature, and high crude oil viscosity at reservoir temperatures. In the current production process, the central area of P601 is undergoing high-frequency huff and puff operations, facing certain problems such as decreasing production, low recovery rates, and rapid depletion of formation pressure. Through physical simulation experiments, the various elements of HDNS-enhanced oil recovery technology were analyzed. Nitrogen plus an oil-soluble viscosity reducer can improve the thermal recovery and development effect of super-heavy oil. With the addition of the viscosity-reducing slug, the recovery rate of steam flooding was 58.61%, which was 23.32% higher than that of pure steam flooding; after adding the 0.8 PV nitrogen slug, the recovery rate increased to 76.48%. With the increased nitrogen injection dosage, the water breakthrough time was extended, the water cut decreased, and the recovery rate increased. Nitrogen also plays a role in profile control and plugging within the reservoir; this function can effectively increase the heating range, increase steam sweep efficiency, and reduce water cut. So, the synergistic effects of steam, nitrogen, and viscosity-reducing agents are good. This technology enhances the development of shallow-layer heavy oil reservoirs, and subsequent development technologies are being compared and studied to ensure the sustainable development of super-heavy oil reservoirs.

Research on Key Parameters of Wellbore Stability for Horizontal Drilling in Offshore Hydrate Reservoirs

The South China Sea has abundant reserves of natural gas hydrates, and if developed effectively, it can greatly alleviate the pressure on the energy supply in China. But the hydrate reservoirs in the sea area are loose, shallow, porous, and have poor mechanical properties. During the drilling process, the invasion of drilling fluid into this kind of reservoir is likely to induce mass decomposition of gas hydrate and, in turn, a significant reduction in mechanical strength around the wellbore as well as instability of the wellbore. In this study, in light of the engineering background of exploratory wells at the South China Sea, a temperature and pressure field model in a gas hydrate reservoir at sea during open circuit drilling was established, and then, based on this model, a comprehensive model for the stability analysis of the well drilled in the hydrate reservoir at sea was constructed, both of them with errors of less than 10%. With these two models, the effects of different drilling parameters on wellbore stability were investigated. The gas and liquid produced by the decomposition of hydrates in the formation will increase the pore pressure in the formation, thereby reducing the effective stress in the formation. The closer the formation is to the wellbore, the more thorough the decomposition of hydrates in the formation and the greater the effective plastic strain. Keeping all other conditions constant, the increase in drilling fluid invasion pressure and temperature, as well as reservoir permeability, will lead to a decrease in the mechanical strength of the formation around the wellbore and an expansion of the wellbore yield zone. The results can provide a theoretical reference for the stability analysis at sea.