Rock Permeability Research Articles

Experimental and theoretical investigation of the mechanisms of drying during CO2 injection into saline reservoirs

A viable CO2 storage resource must have sufficient storage capacity, reliable containment efficiency and adequate well injectivity. Deep saline formations stand out in terms of storage capacity and containment efficiency. However, formation brine dry-out and salt precipitation in the near well region could impair CO2 injectivity in deep saline reservoirs, thus reducing their potential for CO2 storage. Core-flood experiments and analytical modelling were used to investigate various mechanisms of external and internal salt precipitation. Particularly, the impact of the extension of the dry-out region on CO2 injectivity was investigated. It was found that, for high permeability rocks, injection of CO2 at relatively low injection rates could result in salt cake deposition at the injection inlet especially under high salinity conditions. It was also found that extension of the dry-out region does not have significant impact on CO2 injectivity. Although the magnitude of CO2 injectivity impairment increased more than two-fold when initial brine salinity was doubled, real-time changes in CO2 injectivity during the drying process was found to be independent of initial brine salinity. We have shown that the bundle-of-tubes model could provide useful insight into the process of brine vaporization and salt deposition in the dry-out region during CO2 injection. This work provides vital understanding of the effect of salt precipitation on CO2 injectivity.

Evolution of reservoir properties of oil shale rocks under hydro-thermal treatment: Investigations from micro- to macro-scale

Treatment with water at sub- and supercritical states which is considered as one of the most promising technologies for oil shale reservoirs development is still understudied. In particular, reliable correlations between most of the reservoir properties and temperature are absent. However, this data may significantly improve the quality of oil recovery predictions applying numerical simulations. This work is devoted to obtaining the dependency between porosity, permeability, organic matter content and temperature through physical modeling of hydrous pyrolysis. A unique experimental program design is proposed to investigate changes in reservoir properties at macro- and micro-scales and connect these changes with composition and pore structure evolution. A set of experiments on hydrous pyrolysis in a closed system was performed at temperatures 110, 250, 300,325, 350, 375, 400, and 450 °C, and the pressure of 23.4 MPa on rock samples of the Bazhenov formation.As a result, the relation between reservoir properties and the temperature was derived, characterized by a few specific temperature zones with particular behaviors of rock porosity and permeability. Effects on reservoir properties were analyzed in a complex way to highlight the mechanisms of void space transformation related both with pore space evolution and reduction. The observed effects include thermal expansion of organic matter with further transformation to synthetic hydrocarbons, formation of new mineral components, mineral matrix swelling and fracturing.

New Model for Absolute Permeability Prediction in Coal Samples: Application of Modified Purcell Model to Mercury Injection Pressure and Nuclear Magnetic Resonance Data.

The permeability of rocks is a critical parameter in many subsurface geological applications, and pore properties measured on rock samples (including rock fragments) can be used to estimate rock permeability. A major use of MIP and NMR data is to assess the pore properties of a rock in order to estimate the permeability based on empirical equations. Although sandstones have been extensively studied, permeability in coals has received less attention. Consequently, in order to obtain reliable predictions for coal permeability, a comprehensive study of different permeability models was performed on coal samples having a range of permeabilities from 0.003 to 1.26 mD. The model results showed that the seepage pores in coals account for the bulk of the permeability, while the contribution of adsorption pores to permeability is negligible. The models that only consider a single pore size point on the mercury curve, such as the Pittman and Swanson model, or those that use the entire pore size distribution, like the Purcell and SDR model, are inadequate for predicting permeability in coals. This study modifies the Purcell model to determine permeability from the seepage pores of coal, resulting in the enhancement of the predictive capability, with an increased R2 and reduction in the average absolute error by approximately 50% compared to the Purcell model. To apply the modified Purcell model to NMR data, a new model was developed that provides a high degree of predictive capability (∼0.1 mD). This new model can be used for cuttings, which could lead to a new method for field permeability estimation.

Flood Management: Solving Conformance or Sweep Efficiency Problems—Part 2: Connecting Problems to Solutions

_ In Part 1 we discussed the process wheel and the first two elements of that wheel, namely candidate selection and problem clarification. In Part 2 we will focus on generating a connection between the problem types as outlined in the conformance problem matrix and various methods of trying to solve these problems. In this section we continue to utilize the conformance problem matrix outlined in Part 1 and incorporate various overlays on this matrix to describe how elements of the conformance solution continuum and the subsection of the continuum, i.e., existing wellbore interventions, can be used to show how these solutions can be effectively applied. Defining the Problem Matrix Prior effort to classify conformance engineering problems have used a linear view of grading problems from easiest to most difficult to control. Probably the most quoted document in this effort is by Seright et al., SPE 84966. Although I don’t disagree with their ranking process, it really doesn’t help us to focus on the most appropriate solution. A different way of classifying conformance problems was developed, briefly described, and presented in Part 1. The conformance problem matrix (Fig. 1) allows us to classify conformance problems based on two primary problem characteristics: the dominant problem flow path (i.e., a VSC [void-space conduit] or permeable rock) and the location of prominent flow control (i.e., near the wellbore or deeper in the reservoir). Although some problems can contain multiple characteristics, the key is to define the most dominant characteristic so it can be solved first. Populating the Problem Matrix Populating the matrix with every problem type that we face within the industry would create a very cluttered chart. One thing to recognize is that the wellbore is a VSC that we created to connect us to the reservoir. Anytime we lose control of how fluid enters the wellbore from the reservoir, we have a VSC. Thus, we start by reviewing the more common problems associated with losing control of the wellbore such as casing leaks, packer leaks or plugs, mis-perforated intervals, cement channels, perforated wrong interval, etc. These problems all fall in the upper left quadrant. Since they are strictly void space or conduit flow, they are controlled totally at the wellbore. The next example helps us understand the importance of geologic controls and understanding. If we have a watered-out layer with no crossflow between layers, this problem falls in the upper right quadrant, since the flow problem is dominated by permeable flow, but due to no crossflow between layers, all the control exists at the wellbore. We then move to the more complex problem of a watered out layer, but one with extensive crossflow between layers. This problem would fall in the lower right quadrant as the flow problem is permeability related, but since there is extensive crossflow, there is really limited or no control at the wellbore. These last two problems exist as a continuous grade from the upper right quadrant to the lower right quadrant, depending on the level of crossflow between layers.

Application of a Modular Dynamic Formation Tester on a Wire Line to Refine the Filtration Characteristics of the Production Formations of the Magovsky Oil and Gas Condensate Field

An important task in monitoring the development of hydrocarbon fields is to obtain data on the filtration characteristics of reservoirs and the properties of fluids in reservoir conditions. When using standard logging in the complicated conditions of low-permeability formations, poorly consolidated rocks and eroded wellbores, it is very difficult to perform reservoir pressure measurements, sampling with a detailed analysis of fluid properties. A study was carried out in order to clarify the filtration properties of the rocks of the geological section by the method of hydrodynamic logging with testing of the formations by a tester on a MDT logging cable (modular dynamic tester). This problem was solved using the example of carbonate production formations of the Magovskoye oil and gas condensate field, which are generally characterized by a complex heterogeneous structure. An analysis of the effectiveness of using a modular dynamic reservoir tester made it possible to clarify the boundaries of permeable rock intervals with an assessment of their saturation. At the same time, working intervals of the geological section were established, which, with standard logging, were interpreted as dense rocks.

FOAM ACID FRACTURE AS AN ALTERNATIVE TO STANDARD FRACKING AND LIQUID-LESS METHODS OF ROCKS LIQUIDATION

The article discusses the issue of the resource potential of tight terrigenous gas-saturated reservoirs, which lie at significant depths within the central part of the Dnipro-Donetsk oil and gas-bearing region, and ways to solve problems related to the methods of development of these deposits, since they are non-convective and cannot be extracted by the classical method. Within the scope of this issue, the article considers the method of hydraulic fracturing as one of the most effective ways of causing the inflow of hydrocarbons from the productive horizon and intensifying the development of hard-to-extract deposits. An overview of fracturing substances used for the process of densification of rocks, in particular, liquids based on water, hydrocarbon, acid bases, liquid-free methods and foam systems, was performed. The compositions of the reagents, the features of their use, and their main disadvantages are listed. Examples of world experience in the use of well-known fracturing fluids and fluid-free methods of reservoir densification are given.In this work, attention is focused on increasing the permeability of rocks through the use of foam acid systems, since, as experience shows, they are highly effective in conditions of tightand heterogeneous reservoirs due to their selectivity, they can be adapted to rocks of various lithological and mineralogical composition and a wide range thermo-baric conditions, they have satisfactory transport properties and the ability to cause self-cleaning of the well.The main reasons for popularizing the use of methods of loosening rocks with a minimum liquid content in the composition of explosive substances for unconventional gas deposits of Ukraine are highlighted. It is recommended to carry out work on the creation of more effective, ecological and economically profitable new or improvement of existing disintegrants, especially foam systems.

Impact of effective stress on permeability for carbonate fractured-vuggy rocks

To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs, several core models with different structural characteristics were designed and fabricated to investigate the impact of effective stress on permeability for carbonate fractured-vuggy rocks (CFVR). It shows that the permeability performance curves under different pore and confining pressures (i.e. altered stress conditions) for the fractured core models and the vuggy core models have similar change patterns. The ranges of permeability variation are significantly wider at high pore pressures, indicating that permeability reduction is the most significant during the early stage of development for fractured-vuggy reservoirs. Since each obtained effective stress coefficient for permeability (ESCP) varies with the changes in confining pressure and pore pressure, the effective stresses for permeability of four representative CFVR show obvious nonlinear characteristics, and the variation ranges of ESCP are all between 0 and 1. Meanwhile, a comprehensive ESCP mathematical model considering triple media, including matrix pores, fractures, and dissolved vugs, was proposed. It is proved theoretically that the ESCP of CFVR generally varies between 0 and 1. Additionally, the regression results showed that the power model ranked highest among the four empirical models mainly applied in stress sensitivity characterization, followed by the logarithmic model, exponential model, and binomial model. The concept of “permeability decline rate” was introduced to better evaluate the stress sensitivity performance for CFVR, in which the one-fracture rock is the strongest, followed by the fracture-vug rock and two-horizontal-fracture rock; the through-hole rock is the weakest. In general, this study provides a theoretical basis to guide the design of development and adjustment programs for carbonate fractured-vuggy reservoirs.

Pore Structure and Permeability Variations during Gas Displacement in Unconsolidated Sandstone Reservoirs through CT Reconstruction Analysis

The continuous gas displacement in unconsolidated sandstone gas reservoirs will necessarily result in the pore structure and rock permeability variations, which cannot be neglected in the gas development process. However, the variations have not been comprehensively addressed yet, especially for the rock structure in pore scale. This work presented the quantitative results of pore structure in microscale and permeability variations during gas displacement in unconsolidated sandstone reservoirs through computed tomography (CT) reconstruction analysis. The results indicated that a more than 3% increase in porosity after gas displacement resulted from the enlargement of the pore and throat with a diameter of more than 20 μm and 3 μm, respectively, owing to the release and migration of clay and fine particles, in spite of the distribution frequency decline of both pore and throat with a small diameter. The pore connectivity would be enhanced by the increase of the connected pores as well as the enlargement of the pore and throat sizes. However, the pore-throat coordination number could only change with slight improvement. In terms of permeability and relative permeability changes with pore structure, the improvement of permeability after gas displacement was higher than that of porosity, and the continuous gas displacement would broaden gas-water flow region and lower irreducible water saturation and residual gas saturation, and then, the equal phase relative permeability point would shift to the right. These investigations will contribute to more accurate reserve evaluation and productivity prediction.

Miocene tropical storms: Carbonate framework approaches and geochemistry proxies in a reservoir model

The Bragantina Platform is an important sedimentary package that occurs in northwestern Brazil, typically around the equatorial western Atlantic coast. Most of the latest Neogene succession of this carbonate-siliciclastic platform consists of the Pirabas Formation of Miocene age (Burdigalian to Serravalian). High-energy coastal storms and hurricanes as a consequence of trade wind anomalies during the Neogene impacted the shallow-water inner marine heterozoan assemblage deposits of the Pirabas Formation. A chaotic overlap of benthic infauna and epifauna, and of demersal and pelagic species in the same section was analyzed using petrography, petrophysics, micro- and macropaleontology, taphonomy, and geochemistry in order to understand sedimentary and paleoenvironmental processes. The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. This high-energy wave environment caused severe damage to shallow-water heterozoan assemblages at the seafloor, resulting in chaotic faunal arrangements, and removing fine-grained particles thus improving the petrographic properties of the rock (porosity and permeability).

A Survey on the Shortcomings of the Current Rate of Penetration Predictive Models in Petroleum Engineering

In drilling engineering, the rate of penetration (ROP) is a prevalent indicator to evaluate the energy efficiency of drilling operations. Nowadays, ROP prediction has become more critical since the production from deeper hydrocarbon resources is unprecedentedly escalating. So far, a wealth of theoretical and practical investigations has been conducted to develop ROP models; however, the existing models have not been adequately updated with the new technological advancements or geological restrictions. This research strives to integrate the latest advancements, restrictions, and future requirements in ROP prediction. To do this, the existing empirical and data-driven ROP models are elaborated and compared. From the conducted research, it was deduced that four uncontrollable factors, including the rock permeability, wellbore inclination, temperature, and rock hardness, have not been adequately considered in ROP models. Moreover, although data-driven ROP models deliver more accurate results than the empirical models, the determination of the number and type of the input parameters is still challenging. To tackle this issue, it is recommended to develop a formation-based classification system of input parameters for future investigations. This inclusive review can be adopted by the companies and engineers involved in drilling operations to update and reform their drilling strategies.

A similarity solution for a pre-existing fluid driven fracture in a permeable rock

The problem of a two-dimensional, pre-existing, fluid-driven fracture propagating in a permeable rock is investigated. The fracturing fluid is a viscous, incompressible Newtonian fluid and the flow of fluid inside the fracture is laminar. The elasticity of the rock is modelled using the Cauchy principal value integral derived from linear elastic fracture mechanics. With the aid of lubrication theory, a nonlinear partial integro-differential equation relating the fracture half-width to the pressure and leak-off velocity is derived. Similarity solutions are derived for the fracture half-width, pressure and leak-off velocity and are used to reduce the partial integro-differential equation to an ordinary integro-differential equation. In order to close the problem, a model in which the leak-off velocity is proportional to the fracture half-width and the gradient of the fluid–rock interface was used. Numerical results are obtained for the fracture length, fracture half-width and the net fluid pressure.

Comparison of the Permeability of Potential Ballast Rocks from Northern Rio de Janeiro State under Different Fouling Rates after Sodium Sulfate Attack.

This paper aimed to analyze the reduction in the ballast layer permeability simulated in a laboratory in saturated conditions by the presence of rock dust as a contaminant of three types of rocks explored in different deposits in the northern region of the state of Rio de Janeiro, Brazil, through laboratory testing relating the physical properties of rock particles before and after sodium sulfate attack. Sodium sulfate attack is justified by the proximity of some sections of the planned EF-118 Vitória-Rio railway line to the coast and of the sulfated water table to the ballast bed, which could degrade the material used and compromise the railway track. Granulometry and permeability tests were performed to compare ballast samples with fouling rates of 0, 10, 20, and 40% rock dust by volume. A constant head permeameter was used to analyze hydraulic conductivity and establish correlations between the petrography and mercury intrusion porosimetry of the rocks, namely two types of metagranite (Mg1 and Mg3) and a gneisse (Gn2). Rocks, such as Mg1 and Mg3, with a larger composition of minerals susceptible to weathering according to petrography analyses, tend to be more sensitive to weathering tests. This, in conjunction with the climate in the region studied, with average annual temperature and rainfall of 27 °C and 1200 mm, could compromise track safety and user comfort. Additionally, the Mg1 and Mg3 samples showed greater percentage variation in wear after the Micro-Deval test, which could damage the ballast due to the considerable changeability of the material. The mass loss caused by abrasion due to the passage of rail vehicles was assessed by the Micro-Deval test, with Mg3 (intact rock) declining from 8.50 ± 1.5 to 11.04 ± 0.5% after chemical attack. However, Gn2, which exhibited the greatest mass loss among the samples, showed no significant variation in average wear, and its mineralogical characteristics remained almost unchanged after 60 sodium sulfate cycles. These aspects, combined with its satisfactory hydraulic conductivity rate, indicate that Gn2 is suitable for use as railway ballast in the EF-118 railway line.

Investigation of the effect of Fe3O4/SiO2 nanofluid on asphaltene adsorption and wettability alteration in hydrocarbon reservoirs: Optimization of nanocomposite composition and nanofluid concentration

One of the most efficient ways to extract hydrocarbons is to use nanoparticles for wettability alteration, to address dwindling reservoirs and growing energy demand. Another crucial factor is inhibiting asphaltene precipitation, which can cause damage to production components and alter the rock's wettability and permeability. This study investigates the impact of synthesized Fe3O4, SiO2, and Fe3O4/SiO2 nanomaterials on wettability alteration and asphaltene removal in an oil/water system at two temperatures (25 °C and 80 °C). The nanocomposites with various ratios were manufactured with the aid of the sol-gel method and characterized using FTIR, XRD, and dynamic light scattering analysis. The stability of different concentrations of nanofluids was assessed via sedimentation tests and zeta potential measurements. According to the results, there was a reduction in both surface energy and oil area fraction from 89.46 to 8.13 mN/m and from about 1–0.075, respectively. Maximum wettability alteration (from 155° to 32°) was achieved at the optimum condition (0.075 wt% of C1000 at 80 °C). The C1000 nanocomposite played a significant role as an inhibitor in shifting the onset point to higher concentrations of n-heptane compared to Fe3O4 and SiO2 nanoparticles. Furthermore, nanomaterials have a better association with the Langmuir model, and the asphaltene particles are adsorbed homogeneously and in the form of one layer of adsorbents. The results of this study can assist the petroleum sector in better controlling asphaltene precipitation and enhancing oil recovery by C1000 nanoparticles, leading to a higher recovery rate and a more cost-effective production approach.

Geochemical Effects on Storage Gases and Reservoir Rock during Underground Hydrogen Storage: A Depleted North Sea Oil Reservoir Case Study

In this work, geochemical modelling using PhreeqC was carried out to evaluate the effects of geochemical reactions on the performance of underground hydrogen storage (UHS). Equilibrium, exchange, and mineral reactions were considered in the model. Moreover, reaction kinetics were considered to evaluate the geochemical effect on underground hydrogen storage over an extended period of 30 years. The developed model was first validated against experimental data adopted from the published literature by comparing the modelling and literature values of H2 and CO2 solubility in water at varying conditions. Furthermore, the effects of pressure, temperature, salinity, and CO2% on the H2 and CO2 inventory and rock properties in a typical sandstone reservoir were evaluated over 30 years. Results show that H2 loss over 30 years is negligible (maximum 2%) through the studied range of conditions. The relative loss of CO2 is much more pronounced compared to H2 gas, with losses of up to 72%. Therefore, the role of CO2 as a cushion gas will be affected by the CO2 gas losses as time passes. Hence, remedial CO2 gas injections should be considered to maintain the reservoir pressure throughout the injection and withdrawal processes. Moreover, the relative volume of CO2 increases with the increase in temperature and decrease in pressure. Furthermore, the reservoir rock properties, porosity, and permeability, are affected by the underground hydrogen storage process and, more specifically, by the presence of CO2 gas. CO2 dissolves carbonate minerals inside the reservoir rock, causing an increase in the rock’s porosity and permeability. Consequently, the rock’s gas storage capacity and flow properties are enhanced.

Influence of rock permeability and surface conditioning on carbonate wettability: A link between contact angle and Amott-index

The wettability of crude oil/brine/rock system is of great importance in determining oil recovery during water displacement processes. The wetting behavior of rocks has traditionally been assessed via a range of experimental techniques such as the Amott tests and contact angle measurements. While the Amott wettability is known to be influenced by a range of factors, still the impact of rock permeability, rocks surface/saturation condition and initial water saturation remains unclear. Furthermore, a link between Amott wettability and contact angle is missing which is vital to characterize macroscopic vs. core scale wettability. Therefore, in this study, we investigated the effect of permeability, rocks surface/saturation condition and initial water saturation on Amott tests and contact angle measurements using Indiana limestone. We further attempt to experimentally explore the relationship between the contact angle and Amott-Harvey wettability index (IAH) for different rocks. We demonstrated that, in addition to surface texture (roughness) and surface chemistry (heterogeneity), rock surface wetting behavior depends also on the rock permeability and surface/saturation condition (Dry,Sw=1,Sor,SwirrandSo=1). Moreover, a comparison of the observed values for the Amott and contact angles, showed that only when the rock has moderate to high permeability (up to 15.17 mD) will the Amott index corresponds to the wetting state estimated using contact angle method. The influence of several factors on wettability via IAH and contact angle is evident. While permeability demonstrated a positive correlation with wettability, Sor exhibited a negative correlation. For water-wet rocks, contact angle showed weak positive correlation with IAH, while negative correlations were observed in the case of intermediate- and oil-wet rocks. In addition, exceptions were found in the correlations; unlike the IAH, contact angle is weakly correlated with both Sor and Swi obtained from the imbibition experiments. Lastly, spontaneous imbibition time becomes slower and tends to underestimate IAH as rock permeability decreases. The findings from this study will thus broaden the understanding of the interplay of different petrophysical parameters and the relationship between different wetting indices.

Hydrogen tightness evaluation in bedded salt rock cavern: A case study of Jintan, China

Hydrogen is regarded as one of the most important energy sources for the future. Safe, large-scale storage of hydrogen contributes to the commercial development of the hydrogen industry. Use of bedded salt caverns for natural gas storage in China provides a new option for underground hydrogen storage (UHS). In this study, the physical properties of multicomponent gases in UHS and salt rock are reviewed and discussed, along with the flow of hydrogen in the surrounding salt rock. Mathematical models of the two-phase multicomponent flow of the gas–brine system in the UHS were established. A numerical model of a simplified elliptical salt cavern was built to simulate the migration of the gas–brine system in the UHS. The hydrogen tightness of the UHS was evaluated through simulation with different storage strategies, salt rock and interlayer permeabilities, and gas components. The results indicate that: (1) Cyclic injection and withdrawal facilitate hydrogen leakage, which is accelerated by increasing the frequency. (2) The huff-n-puff of hydrogen gas in the injection and withdrawal cycles forces the gas into pore space and enhances the relative permeability of the gas phase. The migration of hydrogen and brine weakens the hydrogen tightness. Brine saturation is an important index for evaluating the hydrogen tightness of UHS. (3) The leakage rate of UHS increases with an increase in the permeability of the salt rock and interlayer and the total thickness of the interlayers. The average permeability Kwa weighted by the thickness of layers for the bedded salt formation is proposed to integrate three variables to facilitate field application of the simulation results. The critical Kwa is less than 3.02 × 10−17 m2 if the recommended annual hydrogen leakage rate is less than 1%. (4) The difference between hydrogen and other gas species is another important factor in the leakage rate and should be considered. This study provides theoretical guidance for evaluating the feasibility of UHS in salt caverns and site selection in China.

A novel method to estimate the Stress-Dependent Kozeny-Carman constant of Low-Permeability, clastic sedimentary rocks

The stress-dependent permeability of low-permeability sedimentary rocks has seized attention because of the growing need for fossil fuels, geological carbon sequestration, and radioactive waste disposal. The Kozeny-Carman equation (K-C equation) is a well-known model for predicting the permeability of sedimentary rocks. The Kozeny-Carman constant (K-C constant, ckc) in the K-C equation accounts for the shape of the pores and the complexity of the pore conduit geometry in rocks. The pore structure of rocks varies owing to compaction at different burial depths. Therefore, the ckc is stress-dependent, a key parameter for understanding the stress-dependent permeability of rocks. However, measuring the stress-dependent ckc in low-permeability rocks is challenging. The present study proposes a novel approach for measuring the stress-dependent ckc of low-permeability rocks. The key elements of the proposed approach are (1) utilizing the Klinkenberg slip factor to evaluate the pore structure of rocks under stress, and (2) measuring rock porosity and permeability simultaneously under stress. This study amended the existing apparatus to fulfill the aforementioned purpose. Silty sandstone and clayey siltstone were selected to illustrate the novel ckc measurement method. The measured ckc values were compatible with the measurement results of documented sandstones and mudstones (most stress-independent). Interestingly, the ckc increased with increasing effective confining stress but started to decrease when the applied stress exceeded a certain critical value. Finally, we provide a synthetic case demonstrating the importance of considering stress-dependent ckc for permeability prediction under stress. If we neglect the stress dependence of ckc, the prediction of permeability using the K-C equation can induce errors up to several orders of magnitude.

Formation damage and improved recovery in kaolinitic high enthalpy gas fields with fabric geological settings

This paper investigates the fines migration and transport in natural gas reservoirs as a function of porous rocks with fabric geological settings. So, an analytical and surface thermodynamic model was developed for high temperature permeable media. Two sets of core flood experiments were conducted under normal (50 °C) and high temperature (150 °C) fluid flow, where the major results revealed that there is an increase in the rock core thermal expansion of 57 (10−6°C−1) and 192 (10−6°C−1) at 50 °C and 150 °C. The rock core underwent a thermal strain to 0.36% and 0.86% under normal and higher temperature conditions. At 50 °C the pressure stabilized to 20 psi and 50 psi was recorded as the peak pressure under 150 °C rock temperature. The fines concentration under higher temperature is significantly higher than the normal rock temperature and yielded maximum up to 77.28 ppm. The rock permeability exhibited a linear and stabilized decline, but at higher temperature new surface energies was created in the rock core and as a result, the reservoir permeability begun to rebound. Microstructural images revealed that the kaolinite clay fine particle under 50 °C has a platelet structure and has multiple straining mechanism. Whereas, under higher temperature the clay fines have transcended to compaction over the rock surface fabrics. Exponential gas recovery of 15% and 25% was observed for both 50 °C and 150 °C cases. In the former case, a linear growth rate to 25% was noted and then gradually it fell to 12.9%. While, in the latter case the gas recovery rate climbed to 33.7% and stabilized, which indicates that the gas recovery rate was monotonous. The experimental and analytical models have been verified using multiple linear regression method and the model's outcome revealed an excellent agreement whose R2 values were found to be 0.9997 and 0.9995.

Evolution of permeability and pore structure of salt rock and its self-healing mechanism under coupled thermo-hydro-mechanical environment

The self-healing characteristic of salt rock under the coupled thermo-hydro-mechanical (THM) environment is important for the safety assessment of underground repositories. In order to study the evolution of permeability and pore structure of salt rock and its self-healing mechanism under the coupled THM environment, the salt rock is treated with self-designed high-temperature and high-pressure THM coupled equipment. The pore/fissure evolution of the specimens is observed by computerized tomography (MCT) and metallographic microscopy and compared with the characteristic of salt rock after heat treatment only. The results show that (1) the salt rock after high-temperature treatment only does not have healing properties from 25 to 700 °C, and the salt rock damage increases sharply when the temperature is higher than 500 °C; (2) under the coupled THM environment, the pressure and temperature make some pores and fissures of the salt rock appear to heal. It is not that the higher the pressure and temperature, the stronger the healing effect, but there is an overall complex competing effect of damage and healing. When the temperature is 25–400 °C, the damaging effect is higher than the healing effect, so the overall microscopic parameters increase; when the temperature is 400–500 °C, the healing effect in the competing relationship is greater than the damaging effect, and the overall microscopic parameters decrease; when the temperature is 500–700 °C, the damaging effect dominates, the overall microscopic parameters increase sharply, and the damage is severe. The healing effect is best in the temperature range of 400–500 °C.

Motion through a viscous liquid sphere enclosed by a solid core embedded into a Brinkman medium

AbstractThe flow around a solid spherical particle encased in a Newtonian liquid sphere and immersed in a couple stress fluid medium is studied. The problem is expressed by using the Brinkman and Stokes equations, which describe both the flow outside and inside the liquid sphere, respectively. The Gegenbauer polynomials and modified Bessel function are used to express the stream function solution for the internal and external regions. An analytical determination for the flow field in terms of stream function is examined by wielding the method of separation of variables. The drag force on a solid spherical particle placed in a permeable region is calculated. On the drag coefficient, the effects of the permeability κ, the viscosity ratio γ2, and the couple stress parameter λ are investigated. Corresponding dependencies (such as the permeability parameter, couple stress parameter, viscosity ratio, and separation parameter) are graphically represented and discussed. The findings shows when the separation parameter is increased the drag coefficient gradually increases, it refers to a sphere surface with a high level of flow resistance. Passages to the limits are used to describe known specific cases. The present study is essentially significant in the course through a layer developed by penetrable particles and has very important and persuasive applications both in nature and innovation, with various potential outcomes. Thus, the discoveries of this article are comprehensively pertinent to the investigation of the flow of permeable liquids past spherical permeable rocks, aloxite materials, sand beds, earthen soil, petrol supply rocks, and so forth. The present application will support in planning a productive bearing framework.