Free Gas Volume Research Articles

Estimation of Shale Gas Reserves: A Modified Material Balance Equation and Numerical Simulation Study

This study presents a comprehensive material balance equation (MBE) to estimate the reserve of shale gas reservoirs including free and adsorbed gas volume. The presented material balance equation takes into account the effect of stress change, matrix shrinkage, water volume production and influx, and critical desorption pressure. The material balance equation is converted into a linear relationship between the reservoir production and expansion parameters used during the derivation procedures that include rock-fluid properties and production history data. The proposed straight line reserve evaluation technique yields a slope of original free and absorbed gas in organic matrix, while the y-intercept yields the volume of original free gas in the in-organic matrix. A field case study of shale gas located in Australia is presented. Results show that the proposed MBE and the corresponding straight line reserve evaluation technique are rational and competent in estimating the free gas and adsorbed gas volumes accurately with error less than 6% compared to the numerical simulation model presented in this study using an in-house simulator based on finite element technique and FORTRAN language. Hence, the presented technique in this study can be used as a quick and easy to use tool to accurately estimate the free and adsorbed gas reserves and to improve the development of the production strategies of shale gas reservoirs.

Salt Diapir‐Driven Recycling of Gas Hydrate

AbstractBy harnessing both hypothetical, synthetic basin and gas hydrate (GH) system models and real‐world models of well‐studied salt diapir‐associated GH sites at Green Canyon (Gulf of Mexico) and Blake Ridge (U.S. Atlantic coast), we propose and demonstrate salt movement (and in particular, diapirism) to be a new mechanism for the recycling of marine GH. At Green Canyon, for example, we show that by considering this newly proposed diapir‐driven recycling mechanism in conjunction with previously proposed lithological control on sandy‐reservoir‐hosted hydrate at the base of the GH stability zone (BGHSZ; ∼bottom‐simulating reflector, BSR), modeled GH saturations match drilling data. Overall, salt diapir movement‐induced GH recycling provides a temperature‐driven mechanism by which GH saturations at the BGHSZ may reach >90 vol. % and by which GH volumes near and free gas volumes beneath the BGHSZ may be increased significantly through time. Interestingly, comparison of salt diapir‐driven recycling and sediment burial‐driven recycling scenarios suggests notably higher rates of recycling via diapir‐driven versus burial‐driven processes. Our results suggest that GH and associated free gas accumulations above salt diapir crests represent particularly attractive targets for unconventional and conventional hydrocarbon resource exploration and for scientific and academic drilling expeditions aimed at exploiting GH systems. Salt basins containing GH systems—including passive margin basins of the Gulf of Mexico, southeastern Brazil, and southwestern Africa—are therefore compelling localities for studying salt‐driven GH recycling and for salt diapir‐associated natural gas exploration.

Occurrence and Migration Mechanisms of Methane in Marine Shale Reservoirs

The occurrence mechanism of methane is very important as evaluating the gas-bearing properties of marine shale reservoirs, and the evaluation of the development effect of shale gas wells need to focus on the migration mechanism of methane. In this study, LTNA technology and NMR technology were used to analyze the pores and methane of shale. The results show that inorganic pores have better connectivity, larger pore size, and micro–nano cracks between pores compared to organic pores. Most of the pores in shale are micropores and mesopores, which provide most of the specific surface area, but the contribution of macropores to pore volume cannot be ignored. Adsorbed gas volume depends on the pore surface area and gas pressure, while free gas volume depends on pore volume and gas pressure. The pore structure of micropores and mesopores is complex, and the specific surface area is large. The dispersion force between pore surface molecules and methane molecules is firm, which makes the pore wall an ideal enrichment space for adsorbed gas. Macropores have larger pore volumes and can store more free gas. In the process of gas well development, free gas is first discharged from pores under the action of the pressure gradient. As the pore pressure is lower than the critical desorption pressure, adsorbed gas begins to desorb in large quantities. It should be noted that the desorption process of adsorbed gas is slow and persistent, which makes it impossible for gas wells to achieve higher recovery in a shorter production cycle. Therefore, improving the recovery rate of adsorbed gas is the key to future research on shale gas development effects. This study is helpful in clarifying the occurrence and migration mechanism of methane in marine shale reservoirs and guiding the development of gas wells.

The Pore Structure of Marine to Continental Transitional Shales in the Permian Shanxi Formation on the East Margin of the Ordos Basin, China

The pore structure is an important factor in determining the storage capacity for shale gas development. Twelve samples were selected from the marine to continental transitional shales in the Shanxi Formations on the eastern margin of the Ordos Basin, and their nanoscale pore structure was investigated by a variety of low-temperature N2 adsorption (LT-N2GA) and low-pressure CO2 adsorption (LP-CO2GA) and high-pressure mercury intrusion (HPMI) experiments. The shale pores are complex and are mainly mesopores, which range mainly from 10 nm to 40 nm and greatly contribute to the pore volume (PV), whereas pores with a diameter less than 0.8 nm greatly contribute to the specific surface area (SSA) of the shale. The pore structure is affected by the TOC content, organic matter maturity, and illite/smectite (I/S) mixed layer content. The total PV increases with the increase in TOC content, organic matter maturity, and I/S mixed layer content. The effects of pores on the occurrence shale gas were determined by high-pressure methane adsorption experiments. The maximum adsorption amount of methane was positively correlated with the SSA of the micropores, indicating that the micropores have a large SSA, which controlled the adsorbed gas content of the shale. The mesopores provide the majority of the PV, which mainly corresponds to the volume of free gas in the shale, and the macropores are mainly micron-sized pores, which can form the main migration channels for shale gas.

Flow regimes characteristics of industrial-scale center-rising airlift reactor

• Multiphase fluids in industrial-scale CRALR exhibit unique flow characteristics. • Δ P - u g curves increase stepwise with gradually rising in distributor hole area. • Pressure accumulation and release in large distributor form gas-liquid oscillations. • Increase of the CRALR diameter induces the bubble stream to rotate in advance. • Limit of gas holdup is determined by equipment parameters. Airlift reactors are frequently preferred in biochemical engineering, and related investigations are almost performed using bench-scale reactors. However, in industrial-scale reactors, multiphase fluid usually exhibits unique mixing and transfer behaviors. Therefore, we studied the flow regimes characteristics in an industrial-scale center-rising airlift reactor (CRALR) with a diameter of 1.2 m. The results show that the available jet hole area of the gas distributor gradually increases along with the superficial gas velocity in the plateau range of the total pressure drop. Since the rise in initial liquid height enlarges the available jet hole area, the flow regime can be transformed from a pure heterogeneous regime to other regimes. Meanwhile, the total gas holdup plunges within the transition regime range, which can be interpreted by the gas–liquid oscillations in the gas distributor with a large free gas volume. When the oscillations cannot maintain the small bubble ratio, the rapid transition from a homogeneous regime to heterogeneous regime is affected. Compared with previous results, the bubble stream rotates in advance in the homogeneous regime of the industrial-scale CRALR. The rotational structure helps to reduce the flow resistance and improves the radial bubble distribution. Furthermore, the total gas holdup curves under various operating conditions converge into one curve at which a limit, determined by equipment parameters, is ultimately reached in the course of increasing the superficial gas velocity. It turns out that the fluids have similar hydrodynamic behaviors in flow fields of different scales when the limit is reached.

Quantification of gas exsolution and preferential diffusion for alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions

The in-situ formation of foamy oil has been found to be a crucial mechanism accounting for the better-than-expected production performance in heavy oil reservoirs under solution gas drive. Not only have the physical laws dominating gas exsolution in foamy oil not yet been well understood, but also the different contributions of each component in a gas mixture to the generation of foamy oil associated with an extremely complicated dynamic process has not been quantified. In this study, a novel and pragmatic technique has been proposed and validated to quantify the gas exsolution and preferential diffusion for alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions by taking gas bubble size distribution and preferential mass transfer of each gas component into account. Experimentally, constant-composition expansion (CCE) tests with various constant-pressure decline rates are utilized to describe gas exsolution behaviour of alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions, during which not only pressure and volume are simultaneously monitored and measured, but also gas samples were respectively collected at the beginning and end of experiments to perform compositional analysis. Theoretically, a mathematical model has been formulated to quantify gas exsolution and preferential mass transfer between each gas component and the liquid phase in alkane solvent(s)–CO2–heavy oil systems under nonequilibrium conditions. More specifically, quasi-equilibrium boundary conditions, real gas equation, and Rayleigh distribution function are combined with the classical equation of motion, continuity equation, and mass transfer equation to form a novel equation matrix for quantifying gas bubble growth in foamy oil. Considering gas bubble size distribution and preferential diffusion of each component in a gas mixture, the total number of gas bubbles and individual diffusion coefficient of each gas component are determined by minimizing the discrepancy between the measured and calculated volume of alkane solvent(s)–CO2–heavy oil systems. More importantly, the dynamic composition of the gas phase and the amounts of both entrained gas and evolved gas can also be obtained simultaneously during the gas exsolution processes. Excellent agreements between the experimentally measured parameters (i.e., volume of foamy oil, composition of evolved gas, and volume of free gas) and the calculated ones have been respectively achieved. Compared with the individual diffusion coefficient for each component in a gas mixture determined under the traditional equilibrium conditions, a relatively large value has been found during mass transfer processes in a supersaturated oleic phase. Moreover, pseudo-bubblepoint pressure and gas exsolution rate are found to be two main mechanisms dominating the volume-growth rate of the evolved gas.

Gas content evolutionin western Guizhou and differential occurrencein China of Permian shale with type III kerogen

Permian organicmatter(OM) in China mainly comes from higher plants rich in type III kerogen. Exploring gas content evolution and occurrence mechanisms is of great significance for shale gas exploration. Shales of western Guizhou in China were collected from wells and subjected to experiments under formation conditions (e.g. thermal simulation, Rock-Eval pyrolysis, X-ray diffraction and CH4 isotherm adsorption). A thermogenic gas generation model was established based on the logistic model, a hydrocarbon expulsion model was established based on the hydrocarbon potential method, and an adsorbed gas volume model was established based on temperature, pressure and total organic carbon(TOC). Various gas content of shale with type III kerogen were calculated in a special geological history. The differences of shales between the western Guizhou and the northeastern Ordos Basin in China were compared in terms of gas generation, expulsion and adsorption capacity. The results showed that the gas generation capacity of the western Guizhou samples was stronger because of the higher TOC and hydrogen index (HI). Limited differences in hydrocarbon expulsion efficiency were observed between the two areas. The source area of the samples had no significant effect on the adsorption capacity. Due to its high TOC, low geothermal gradient, high pressure gradient and suitable burial depth (500–1500 m), the shale in western Guizhou has a stronger adsorption capacity. Obvious differences in the free gas volume and proportion in different areas were observed and should be analyzed separately in combination with the TOC, HI, geothermal gradient, pressure gradient and depth.

Histological Examination of Respiratory Tissues of Dolphins and Porpoises Subjected to Postmortem Blast Exposure

Exposure to explosions often causes morbidity as waves of over-pressure and under-pressure shear interstitial tissue and cause traumatic damage including severe hemorrhage. Respiratory tissues are most at risk due to their proximity to free gas volumes that rapidly and severely contract or expand during blast-induced pressure changes. Unfortunately, we have no medical interventions that can prevent or limit pressure-induced blast damage to tissues. Perhaps such protective technology can be modeled from the respiratory tissue of diving animals that are naturally adapted for pressure changes. Our goal is to characterize any respiratory injuries resulting from postmortem blast pressure exposures. 5 species of freshly dead dolphins (n= 8) and porpoises (n =6) were obtained from naturally occurring strandings were artificially exposed to blast pressures postmortem. Gross observations were made during a necropsy, and respiratory tract tissues were then harvested and processed for histological examination. Blast pressure exposure levels were not revealed to enable unbiased observations. Results indicate that many specimens show dark reddish discoloration of variable intensities that may be evidence of blast-induced trauma. Discoloration was found in the lungs (dark, striped pattern correlating with intercostal spaces between ribs), larynx (above and below palatopharyngeal sphincter), trachea (uniform throughout lumen), and nasal region (visualized only in areas of sloughed lining). Gas containing tissues may exhibit damage due to dramatic compression/expansion to accommodate changing gas volumes. Abrupt edges to discoloration patches indicate protection, possibly conferred by contact with adjacent tissues. Discoloration patterns are consistent in location but have variable intensity, perhaps reflecting different degrees of exposure. Specimens exhibited variable levels of damage to the same organs, perhaps indicating a correlation with received blast pressures. These differences may also indicate a level of resistance to blast damage of tissues that have mechanisms to compensate for pressure changes. Tissue compensation is likely limited to pressure exposures that correspond to naturally occurring diving pressures. Pressures that exceed these levels are presumed to overwhelm tissue compensatory mechanisms. This information may be useful in setting critical exposure limits to prevent harm to odontocetes in the vicinity of a blast event. Further, It is hoped that a discovery of pressure mitigating structures in dolphins can inspire the design of new protective devices for use by people exposed to blast forces.

셰일 및 치밀 저류층의 지화학 및 암석물리 특성 연구동향 고찰

Shale reservoirs has drawn great attention among unconventional resources since the first unconventional extraction of gas from Barnett Shale by Mitchell in 1998. In the beginning, carpet drilling and hydraulic fracturing to shale reservoirs made a great benefit without detailed geological understanding. However, the sudden increase of gas supply and international economic crisis resulted in lower gas price relative to oil price, which requires more detailed development optimization and geological characterization on shale reservoirs to reduce operation cost. In order to evaluate the productivity of shale and tight reservoirs, it is necessary to accurately predict the amount of gas stored in the reservoir. To calculate exact volume of gas in reservoirs, we must reliably measure petrophysical parameters such as permeability, porosity, and water saturation to estimate free gas volume, and geochemical parameters such as total organic carbon (TOC) and adsorption capacity to estimate desorbed gas volume. Several measurement techniques have been proposed to overcome the difficulty in very low porosity and permeability of shale and tight reservoirs. Recently, the crushed rock technique have been used for porosity and permeability of shale and tight reservoir are measured, but the standard procedures have not yet been established. Water saturation is another hurdle since actual measurements are extremely difficult and time-consuming. Modified conventional equations have been tried, but there are still various limitations. We also cover currently available techniques and their limitations on TOC, a measure for gas generation potential, and adsorption capacity. Currently, measurement techniqies for petrophysical and geochemical properties of shale and tight reservoirs are not fully established. There should be detailed studies for the accurate estimation of these properties, which can lead successful reservoir characterization.

Law of imbibition effect on shale gas occurrence state

So far, how imbibition effect changes the occurrence state of shale gas has not been quantitatively understood, and the law of gas–water dynamic displacement caused by the retention of abundant fracturing fluid in a shale reservoir has not been determined clearly. In this paper, a gas–water displacement experiment was performed to simulate the change in the water content of shale near the wellbore after hydraulic fracturing. Then, based on the low field nuclear magnetic resonance spectrum analysis technique of hydrogen-bearing fluid (1H-NMR), the occurrence state of methane in shale reservoirs was dynamically monitored and methane volume in different occurrence states was calculated. Finally, the law of imbibition effect on the occurrence state of shale gas was studied. And the following research results were obtained. First, the process of shale saturation with methane is divided into adsorption-dominant phase and pore-filling phase. And adsorption and pressure gradient play a role simultaneously in the process of shale saturation with methane. Second, in the early stage of the process of shale saturation with methane, priority is given to saturated adsorbed gas, and free methane exists in shale pores as an intermediate state in which the external methane is converted to the adsorbed methane. After the adsorbed gas reaches the saturated state, methane fills shale pores under the pressure gradient until the pressure inside and outside the pores is balanced. Third, imbibition effect leads to the occurrence of gas–water displacement in shale. The adsorbed methane is partially desorbed into free methane, and the proportion of adsorbed gas is reduced. After 80 h' imbibition, the proportion of adsorbed gas is reduced from 63.58% to 45.87%. The increase of free gas volume results in the rise of shale pore pressure. And at the same time, water occupies partial pore volume to compress the storage space of free gas and expel some free gas out of shale pores. In this way, the gas bearing property of the reservoir is deteriorated, and the gas content of the shale sample is reduced to 7.34 mL/g from 7.91 mL/g which is the value before the beginning of imbibition. Fourth, the retention of abundant fracturing fluid in the process of hydraulic fracturing makes the shale reservoir near the wellbore in the state of rich water, the gas–water displacement induced by imbibition effect increases the volume of free methane in the external space (such as shale pore and wellbore), and the increase of pore pressure leads to the rise of the formation pressure, which is beneficial to the exploitation of shale gas to a certain extent.

Spontaneous gastric rupture presenting as severe pneumoperitoneum in a cat with presumed idiopathic gastric ulceration

An 11-year-old female British blue cat was referred for investigation of acute onset vomiting and marked abdominal enlargement. Diagnostic investigations confirmed a large volume of free gas within the abdomen...

Tests of Acoustic Target Strength and Bubble Dissolution Models Using a Synthetic Bubble Generator

AbstractTo test methods used for converting observations of acoustic backscatter to estimates of the volume and transport of free gas escaping the seabed, a bubble generator has been constructed and used at sea. The bubble generator creates individual bubbles of the sizes commonly associated with methane seeps, 1–5-mm radii, which can be released at preplanned rates. The bubble generator was deployed off the coast of New Hampshire at a depth of 55 m, and acoustic backscatter between 16 and 24 kHz was collected from a shipboard echo sounder while transiting over the rising bubbles. Bubble sizes and compositions (either Ar or N2) were known at the source. A model for bubble evolution, accounting for changes in bubble size and composition due to hydrostatic pressure and gas diffusion across the gas–liquid boundary, was coupled with an acoustic target strength (TS) model to generate predictions of the acoustic backscatter from bubbles that had risen to different depths. These predictions were then compared with experimental observation. Good agreement between prediction and observation was found in most cases, with the exception of the largest (4 mm) gas bubbles at depths of 30 m or less. The exact cause of this bias is unknown, but may be due to incorrect assumptions in models for the bubble TS, rise velocity, or mass transfer rate.

Quantifying Gas Content in Coals Using Resonance Borehole Magnetic

Evaluating gas content in coals has significant commercial and operational importance. In coal seam gas exploration and development, gas contained in coal seams is the resource of interest. In coal mining, quantifying gas content and evaluating the effectiveness of degassing is essential to safe mining operations. Traditional approaches to saturation evaluation in conventional oil and gas reservoirs rely on relationships between resistivity and water saturation. These relationships are challenging to apply in coals due to complexities in their pore systems and gas trapping mechanisms. Therefore, geophysical log-based methods are not commonly employed for saturation evaluation, and core canister desorption measurements are the standard approach for gas content evaluation. Desorption measurements present their own challenge due to the unknown and variable volume of gas lost during core recovery, so an in-situ measurement of gas content is desirable. Advanced magnetic resonance measurements are one method of resistivity-independent saturation evaluation that have been employed in the oil and gas industry for the past approximately fifteen years. However, previous approaches to these types of measurements have focused on the evaluation of conventional reservoirs and hence free gas and oil volumes, and have lacked sensitivity to quantify adsorbed gas, which has a different magnetic resonance response. A novel magnetic resonance acquisition scheme has been developed that provides sensitivity to both adsorbed and free gas, as well as water, allowing for the complete evaluation of fluid content in coal seams. This measurement has been employed in evaluating coal gas content for mining optimisation with encouraging results.

Hazardous manifestation of gas-dynamic phenomena in the faces of coal mines

The statistics of coal and gas outbursts in the faces of the Russian coal mines is provided. The mining-geological and mining-engineering conditions for the occurrence of sudden outbursts during the coal mining are considered, and the distinctive features in the factors of their occurrence and behavior are discussed. The criteria for identifying the potentially hazardous zones with the help of geophysical measurements are given. It is shown that it is important to take into account the data on the actual occurrence of outburst hazard in overlying and underlying longwall faces and development workings, as well as the results of the current forecast when preparing the extraction area for mining, as it follows from the results of underground investigations. The features are noted and the concept of the mechanism causing sudden coal and gas outbursts of faces is formulated. According to this concept, the probability of a hazardous situation is minimal at the beginning of the face advancement before the primary roof collapse. After the primary caving, the outburst hazard increases with the face advancement from the place of caving due to increased stresses in the bearing pressure zone, strengthening of the restraint of the nearest roof support, and the formation of a low permeable bridge in the coal seam near the exposed surface of the coal massif, which increases the pressure and free gas volume behind this bridge. The maximum degree of outburst hazard in the cleaning face is reached at the time of secondary roof collapses.

Modeling of Methane/Shale Excess Adsorption Under Reservoir Conditions

Summary Micropores and mesopores are the main storage volumes in shale matrix. Because of their small pore sizes, the force between pore boundary and gas molecules is significant. A larger amount of adsorbed gas is in a shale gas reservoir than in a conventional gas reservoir. People usually measure adsorption through volumetric methods under an isothermal condition. Because of a limitation of volumetric methods, only excess adsorption data are directly measured; then, a chosen model is applied to calculate an absolute adsorption through fitting the measured data. An adsorption process induces changes in free-gas volume. However, the changes in absorbent volume and methane absorption into organic matter also alter the measured gas volume, which is widely neglected in previous studies. In this study, one volume term, which accounts for the unexpected changes in gas volumes caused by the other mechanisms except adsorption, is added to the Dubinin-Astakhov (DA) model (pore-filling theory). The in-situ methane is in a supercritical condition under reservoir conditions. Because of the lack of a saturation pressure of a supercritical fluid, an adsorbed-phase gas density is used to replace the saturation pressure in the DA model. The modified model is validated by the isothermal adsorption data from four different shale plays. The calculated data by the proposed model have a better match with the measured data than those by the DA model. All shale samples demonstrate a nonmonotonic deformation of adsorbent (volume shrinkage in the low-pressure region, then swelling as pressure increases), which coincides with the results of previous molecular simulation. The key parameters of the proposed model such as a maximum adsorption capacity are more accurate and reasonable than the ones of the DA model. The proposed model provides a good approach to quantify absolute adsorption through experimental data, especially under reservoir conditions, and to emphasize the important effects of volume on methane/shale adsorption.

Large deformation and gas retention during cookoff of a plastic bonded explosive (PBX 9407)

We have used several configurations of the Sandia Instrumented Thermal Ignition (SITI) experiment to develop a pressure-dependent, four-step ignition model for a plastic bonded explosive (PBX 9407) consisting of 94 wt.% RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and a 6 wt.% VCTFE binder (vinyl chloride/chlorotrifluoroethylene copolymer). The four steps include desorption of water, decomposition of RDX to form equilibrium products, pressure-dependent decomposition of RDX forming equilibrium products, and decomposition of the binder to form hydrogen chloride and a nonvolatile residue (NVR). We address drying, binder decomposition, and decomposition of the RDX component from the pristine state through the melt and into ignition. We used Latin Hypercube Sampling (LHS) of the parameters to determine the sensitivity of the model to variation in the parameters. We also successfully validated the model using one-dimensional time-to-explosion (ODTX and P-ODTX) data from a different laboratory. Our SITI test matrix included 1) different densities ranging from 0.7 to 1.63 g/cm3, 2) free gas volumes ranging from 1.2 to 38 cm3, and 3) boundary temperatures ranging from 170 to 190 °C. We measured internal temperatures using embedded thermocouples at various radial locations as well as pressure using tubing that was connected from the free gas volume (ullage) to a pressure gauge. We also measured gas flow from our vented experiments. A borescope was included to obtain in situ video during some SITI experiments. We observed significant changes in the explosive volume prior to ignition. Our model, in conjunction with data observations, imply that internal accumulation of decomposition gases in high density PBX 9407 (90% of the theoretical maximum density) can contribute to significant strain whether or not the experiment is vented or sealed.

A comparison study between N-Solv method and cyclic hot solvent injection (CHSI) method

Steam injection is one of the major recovery methods to exploit heavy oil reservoirs. Replacing steam with hot solvent is an innovative idea to immensely decrease environmental pollution and energy consumption in steam-based recovery methods. The current hot solvent injection method attracts attention to the vapor solvent extraction (VAPEX) process. In comparison with the VAPEX process, cyclic solvent injection (CSI) process has been acknowledged as a high oil rate method due to the driving force of foamy oil flow. Hot solvent injection method is potentially applicable in the CSI process, which may increase the oil production rate and avoid the disadvantage of the VAPEX method. In this study, two experiments have been conducted to compare the production performance between the hot solvent-based CSI method and the hot solvent-based VAPEX method. The hot solvent-based CSI method is named the cyclic hot solvent injection method (CHSI). The hot solvent-based VAPEX method refers to the N-Solv method. N-solv is a patented method where the solvent is injected at the dew point temperature under the reservoir pressure condition. Due to the temperature difference between the reservoir and injected solvent, the injected solvent will condense in the reservoir and the condensed solvent will generate latent heat that can heat the reservoir chamber and thus reduce the oil viscosity (Nenniger and Gunnewiek, 2009). In this study, the N-Solv method has been studied in a laboratory test for the first time in N-Solv research history (Cao, 2011; Nenniger, 2005; Nenniger and Gunnewiek, 2009).According to experimental results, either of the two methods demonstrates some advantages in comparison with the other method from various aspects. From the production performance point of view, the recovery factor of the CHSI method is nearly 10% higher than that of the N-Solv method. The longer high oil rate period of the CHSI method in contrast with the N-Solv method indicates that the foamy oil behavior is more beneficial to the oil production compared with the gravity drainage and the solvent diffusion effect. In addition, it is shown from the solvent chamber growth difference that the gas flooding effect can enhance oil production in the CHSI process because the oil from gas-flooded area in the reservoir is clearly extracted out. However, according to the production GOR data, CHSI is a solvent-consuming method where a tremendous volume of free gas tends to be trapped in the solvent chamber as a result of gas flooding, which may offset the positive effect of gas flooding due to large consumption of solvent. The phenomenon of free gas trapping has not been found in the N-Solv process.

Decomposition of Methane Hydrate in the Presence of Sodium Dodecyl Sulfate

Presented work is devoted to the study of the process of decomposition of methane hydrate obtained in the presence of sodium dodecyl sulfate. It was found that the rate of dissociation increases with temperature and surfactant concentration increasing. It was found that free gas volume inside the reactor plays important role in the process of methane hydrate formation and influences on kinetics of hydrate formation and methane concentration in produced hydrate. It has been suggested that the decrease in the gas content in the resulting hydrate is associated with a decrease in the cooling efficiency with a larger reactor load and a decrease in the area of the effective cooling surface of the reactor walls and the formation of a hydrate on the reactor walls that reduces heat exchange between the remaining liquid phase and the refrigerant.

Characterization of a hydro-pneumatic suspension strut with gas-oil emulsion

Abstract The nonlinear stiffness and damping properties of a simple and low-cost design of a hydro-pneumatic suspension (HPS) strut that permits entrapment of gas into the hydraulic oil are characterized experimentally and analytically. The formulation of gas-oil emulsion is studied in the laboratory, and the variations in the bulk modulus and mass density of the emulsion are formulated as a function of the gas volume fraction. An analytical model of the HPS is formulated considering polytropic change in the gas state, seal friction, and the gas-oil emulsion flows through orifices and valves. The model is formulated considering one and two bleed orifices configurations of the strut. The measured data acquired under a nearly constant temperature are used to identify gas volume fraction of the emulsion, and friction and flow discharge coefficients as functions of the strut velocity and fluid pressure. The results suggested that single orifice configuration, owing to high fluid pressure, causes greater gas entrapment within the oil and thus significantly higher compressibility of the gas-oil emulsion. The model results obtained under different excitations in the 0.1–8 Hz frequency range showed reasonably good agreements with the measured stiffness and damping properties of the HPS strut. The results show that the variations in fluid compressibility and free gas volume cause increase in effective stiffness but considerable reduction in the damping in a highly nonlinear manner. Increasing the gas volume fraction resulted in substantial hysteresis in the force–deflection and force–velocity characteristics of the strut.

Geologic structure controls on initial productions of lower Silurian Longmaxi shale in south China

The Lower Silurian Longmaxi shale is the most important marine shale gas play in South China. Several hundred wells have been drilled to date, of which more than 150 wells have obtained high initial production (IP). Outside of the Sichuan Basin, however, wells drilled in the Lower Silurian Longmaxi shale do not reach flow rates that are commercial. Developing an understanding of the key factors controlling the IPs of Longmaxi shale is important in screening shale-resource plays. In this study, the TOC, thermal maturity, porosity, and gas saturation data obtained from Longmaxi shale of southeastern Chongqing area outside Sichuan Basin have been compared with that of Sichuan Basin. The results of this study show that the shales encountered display similar properties including TOC (>2%), thermal maturity (2.5–3.5% EqRo), and total porosity (3–6%). A good correlation between IPs and pressure coefficient suggest that the free gas content of gas shale controls on IPs. Porosity and gas saturation of gas shale are the main factors to control its free gas volume. The gas saturations in Longmaxi shale from high initial production wells in Sichuan Basin mainly range between 50 and 90%, however, that of shale in the southeastern Chongqing area are decreased to 10–30%. This is the directly reason for low IPs of wells. The contrasting gas saturation of Longmaxi shale between Sichuan Basin and the adjacent fold-thrust belts are interpreted to reflect, in part, differences in sealed condition of fluid system. Intensive tectonic movements caused the exhumation, faulting and fracturing, that reduced or destroyed the sealed ability of shale fluid system, which are the major factors for enhancing water saturation, decreasing fluid pressure and IPs. Finally, the study proposes several most favorable zones for Longmaxi shale gas exploration and development.