Coal Seam Methane Research Articles

Experimental Study on Desorption Characteristics of Coalbed Methane under Variable Loading and Temperature in Deep and High Geothermal Mine

Due to the influence of deep high stress, geothermal heat, and other factors, the law of desorption of methane in coal seams is more complicated in the process of mining deep coal seams, which is prone to methane over‐limit, coal and gas outburst, and other accidents. In order to study the desorption characteristics of coalbed methane under different loading and temperature conditions, the desorption tests at different deformation stages of coal containing methane were carried out in the process of loading‐adsorption‐desorption‐reloading until the coal sample was destroyed by using the seepage‐adsorption‐desorption test system on coal and rock mass, and the test programs were different combinations of gas pressure 1.2 MPa, two kinds of confining pressure, and three kinds of temperature. The results show that the cumulative methane desorption amount corresponding to each deformation stage presents a convex parabolic increase trend with the increase in desorption time, while the desorption rate presents a power function decay trend. Under the condition of the same desorption time, the cumulative methane desorption amount from large to small is residual deformation stage, compaction stage, near the peak stress, plastic deformation stage, and elastic deformation stage. Under the same confining pressure, temperature, and methane pressure, the maximum desorption rate from large to small is residual deformation stage, near the peak stress, plastic deformation stage, compaction stage, and elastic deformation stage. The desorption and diffusion of methane are promoted under the higher temperature and lower confining pressure, which presents a certain mechanism of promoting desorption. The thermal movement of methane molecules is intensified with the increase in temperature, and the adsorption effect between methane molecules and the molecules at the surface of the coal is weakened. The cumulative methane desorption amount and the maximum desorption rate increase with the increase in temperature. The cumulative methane desorption in the residual deformation stage is obviously greater than that in other deformation stages. The increase in confining pressure inhibits the development and expansion of pore fractures in raw coal specimen and hinders the increase in the effective desorption surface area. The cumulative methane desorption amount and the maximum desorption rate decrease with the increase in confining pressure.

The Effect of Static Blasting Materials on Coal Structure Changes and Methane Adsorption Characteristics

Methane in coal seam is always under the dynamic process of adsorption and desorption. It has been demonstrated that the static blasting technology is an effective way to extract methane from coal. Although it is of great significance to understand the role of static blasting materials on methane extraction, the change of methane during static blasting is not well understood due to limited research studies. In this paper, we took the reaction pressure and heat from the hydration of the static blasting materials as the main factors. Microstructure changes in the static blasting materials and coal were analyzed by scanning electron microscopy, gas chromatography, infrared spectroscopy, and mercury injection. Changes of methane adsorption and adsorption rate before and after the static blasting were also measured. Our results demonstrated that the static blasting materials entered the microcracks of the coal body and the porosity of the coal was increased by heat expansion, improving methane migration. During the blasting process, methane began to desorb from the coal and its adsorption content was decreased. In contrast, the adsorption of methane was increased after the reaction. However, methane adsorption rate is higher than that of raw coal, indicating that the adsorbed methane is easier to convert into free methane, which is conducive to emission. This is of great significance to methane extraction and the safety of mines.

Effects of moisture on methane desorption characteristics of the Zhaozhuang coal: experiment and molecular simulation

Coal and gas outbursts have occurred in the Zhaozhuang coal mine (a high gas coal mine) since its construction, and these outbursts pose a great threat to lives and property. Therefore, the combination of methane desorption experiments and molecular simulations was adopted to investigate the effects of moisture on the methane desorption characteristics of the Zhaozhuang coal, and the microscopic mechanism was analyzed in this paper. The aim of this work is to provide a method for predicting the effect of moisture on coal seam methane desorption, and quantitatively evaluating the control effect of hydraulic measures on coal and gas outbursts from a molecular perspective. The experimental data (methane desorption amount) were measured under various adsorption equilibrium pressures (0.3 MPa, 0.4 MPa, and 0.5 MPa) and moisture contents (0%, 5%, and 9.8%). Based on the Zhaozhuang coal molecular model, the molecular simulation process was conducted using Materials studio software, which can better match the experimental conditions by setting various pressure parameters (0.3 MPa, 0.4 MPa, and 0.5 MPa) and calculating various numbers of H2O molecules (0, 8, and 16) on the coal molecule. The results show that methane desorption decreases with the increasing moisture content in the experiment. The number of CH4 molecules adsorbed on the coal molecule decreases with the increasing number of H2O molecules in the simulation. This phenomenon can be explained by the competitive adsorption between CH4 and H2O molecule: the interaction between coal molecule and H2O molecules is stronger. The affinity between CH4 molecules and the coal molecule is reduced, and CH4 molecules are less aggregated around the coal molecule because of the presence of H2O molecules.

Super Deep Boring Technology

Fracking, injecting heated water or steam into rock at depth with proppant to hold open cracks and facilitate flows, has changed the world energy market. Instead of shortages predicted by proponents of peak oil formulations, natural gas is now plentiful. Far more plentiful than the oil and gas trapped in classical reservoirs, and even tight gas and coal seam methane, are the vast deposits of deep gas which must exist given vast geophysical evidence. Methane as “fossil fuel” is a misnomer as methane is abundant in the cosmos and at great depths in the earth. To date conventional methods are unable to access this depth. This paper details the need to develop new super deep boring technologies, not just to access deep gas, but to garner geothermal power under every location on Earth. The design and method of rock melting device is presented but independent computations and calculations show that such devices modeled on the subterrene originally developed in Los Alamos Government Labs, although later patented, cannot work. As there is no significant benefit to boring through rock melt or solid rock at great pressure, a self-propelled shaped charge penetrator previously offered as a self-propelled bunker bomb is offered as a viable method to reach depths to access deep gas. Other lucrative applications for this device is also proposed.

Application of CBM horizontal well development technology in the roof strata close to broken-soft coal seams

Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane (CBM) in broken-soft coal seams. In this paper, No.8 coal seam in the Luling Mine of the Huaibei Coal Field was taken as an example to study the way to improve CBM production of broken-soft coal reservoirs. First, drilling, fracturing and production of horizontal wells were considered comprehensively. Then, based on the idea of exploiting CBM through horizontal wells in roof strata close to the broken-soft coal seams, the propagation laws of fractures created by layer-penetrating fracturing of horizontal wells in roof strata were studied, and accordingly the location of horizontal well was optimized. Finally, the CBM horizontal well exploitation technology for the roof strata close to coal seams was developed and tested on site. And the following research results were obtained. First, the vertical fractures created during layer-penetrating fracturing of horizontal wells in roof strata can propagate from the roof strata with high stress values downward to the coal seam with low stress values. In addition, the location of horizontal well has an important influence on the effect of layer-penetrating fracturing. The closer the horizontal well is to the coal seam, the better the fracture propagation effect of layer-penetrating fracturing. Second, the horizontal well should be arranged in the roof strata 1.5 m away from the top of coal seam, so that fracturing stimulation requirements of horizontal wells in roof strata can be satisfied to the uttermost. Third, three key technologies are formed, including the “high-quality, fast and safe” drilling technology, the deep-penetration oriented perforating technology and the “large displacement, large scale, high pad ratio and moderate proppant concentration” active water fracturing technology. Fourth, the gas production with this technology in engineering practice is remarkable. In conclusion, the CBM development technology of horizontal wells in roof strata close to broken-soft coal seams is feasible. The research results provide a new technical method for the development of CBM in broken-soft coal seams.

DEVELOPMENT OF A NEW INDEX FOR METHANE DRAINAGEABILITY OF A COAL SEAM USING THE FUZZY ROCK ENGINEERING SYSTEM

Coal seam gas is one of the most significant energy resources in unconventional gas fields. The identification of influenc- ing parameters and methane drainage assessment are, thus, a prime geotechnical focus for all potential methane drain- age projects. In methane drainage operations of coal seams, many factors, such as natural factors and operational factors affect the drainage efficiency. In this paper, a new coal seam methane drainageability index (CMDI) is introduced for pre-drainage techniques in a working mine. In this approach, seventeen parameters are considered as the main factors affecting the methane drainage form coal seam, and the interaction matrix based on the fuzzy rock engineering system (FRES), which analyzes the interrelationship between the parameters affecting methane drainage activities, are used to study coal seam methane drainageability. Since the value of interaction in the RES method is not unique, the fuzzy sys- tem is used to minimize subjectivity of the weights which are computed in the RES method. The Tabas coal mine (Iran) was selected as a case study and the proposed index was used to rank the C1 seam in this mine. It was observed that the methane drainageability index could suitably predict the potential of the methane drainage of coal seam. The newly proposed index can be used as a basis for decision-making when uncertainties about the evaluation of the parameters affect the methane drainage of a coal seam and reduce the risk of methane drainage projects.

Influence of water invasion on methane adsorption behavior in coal

Fluid displacement is the fundamental process for subsurface fossil fuels extraction. Water invasion in coal seams is one of the routinely used stimulation approaches for coal seam methane extraction in underground coal mines. However, how the invading bulk water interacts with adsorbed/gaseous methane in coal is rarely considered even though it is known that moisture presence in coal decreases methane uptake by occupying adsorption sites. Here we study how the invading water interacts with adsorbed/gaseous methane in molded coal under elevated pressures using a custom-designed instrument; the test procedure mimics the real water invasion process in engineering applications. Experimental results demonstrate that invasion water displaces adsorbed methane in nanopores of coal and thus enhances the free gas content. The displacement mechanism can be attributed to capillary effect and preferential flow in a coating mode. It was found that Philip's sorptivity model can simulate the relationship between displaced methane content and time, and the obtained sorptivity increases with increasing water invasion content and is independent of gas pressure. It was observed that the higher the initial adsorption equilibrium pressure, the larger the displaced methane content, and this can be attributed to the pressure-dependent feature of adsorbed methane density. The higher the invasion water content, the higher the displaced methane content. These experimental results are also applied for optimizing gas drainage borehole arrangement to efficiently drain coal seam gas in underground coal mines. These findings provide a new perspective to understand the interactions between bulk water and methane in coals and pave the way for developing new technologies for methane recovery in coal seams.

Laboratory Evaluation of Soil Amendments To Limit Structural Degradation under a Sequential Irrigation with Coal Seam Gas and Rain Water

Core Ideas Land amendment irrigation was effective at reducing structural decline under rapid dilution. Threshold electrolyte concentration analysis and initial Ksat are crucial management factors. High‐frequency rainfall events may cause concern for marginal quality water use in irrigation. Land amendment irrigation (LAI) has become an increasingly useful practice in addressing sodic and alkaline coal seam methane gas (CSG) water for irrigation purposes. However, there is a paucity of information pertaining to rapid dilution of soil solution under LAI management. This study investigated the ability of land amendment to buffer soils against structure degradation under sequential irrigation with CSG water (electrical conductivity [EC], 3 dS cm–1; sodium adsorption ratio [SAR], 100 mmolc L–1; pH 8.4) and rainwater in a highly smectitic black Vertisol (BV) and kaolinitic Oxisol (OX) soil. Stoichiometric quantities of gypsum and sulfur amendments were applied for the LAI process to reduce sodicity and alkalinity to a target of SAR ≤20 and HCO3− alkalinity ≤100 mg L–1. Soils were irrigated with 10 ML ha–1 CSG water and 9 ML ha–1 rainwater in the sequence of 1 ML ha–1 and 0.9 ML ha–1 CSG water and rainwater events, respectively, using a 7.5 mm h–1 rainfall intensity. Saturated hydraulic conductivity was determined and reported as a reduction from initial conductivity. The collected leachates were used for subsequent measurements of pH, EC, SAR, and alkalinity at each event. Results suggested that LAI was inadequate to protect soil structure from more than three of the intensity–frequency–duration events but sufficient for up to three events. This was considered positive evidence for LAI given the annual recurrence of such an event was one for the region. Additional gypsum application had no significant effect on protecting soil from further hydraulic reduction compared with LAI alone. The OX and BV behaved differently in terms of the observed hydraulic reduction, which was determined to be both a function of iron oxides (OX) and the effect of dilution, in contrast to the threshold electrolyte concentration. This highlighted that both the initial hydraulic conductivity and threshold electrolyte conditions are important in implementing LAI.

Undesorbable residual gas in coal seams and its influence on gas drainage

The definition of “residual gas” can be found in different scenarios, such as the “fast” and “slow” desorption methods of measuring gas content and the sorption hysteresis test and gas management of coal mines, however, its meaning varies a lot in different contexts. The main aim of this paper is to discuss the existence of truly undesorbable residual gas in coal seam conditions and its impacts on sorption model and gas drainage efficiency. We believe the undesorbable residual gas does exist due to the observation of the extended slow desorption test and the sorption hysteresis test. The origin of undesorbable residual gas may be because of the inaccessible (closed or semi-closed) pores. Some gas molecules produced during coalification are stored in these inaccessible pores, since the coal is relatively intact in the coal seam condition, these gas molecules cannot escape during natural desorption and then create the undesorbable residual gas. Based on the existing adsorption models, we propose the improved desorption versions by taking into consideration the role of residual gas. By numerically simulating a gas drainage case, the gas contents after different drainage times are studied to understand the influence of residual gas content on gas drainage. The results indicate that the influence starts to be obvious even when the total gas content is at a high level, and the impact becomes more and more apparent with increasing drainage time. Our study shows that the existence of residual gas will impede the gas drainage and the total amount of recoverable coal seam methane may be less than expected.

CO2 gas fracturing: A novel reservoir stimulation technology in low permeability gassy coal seams

Coal mine methane (CMM) is one of the major safety hazards in China’s gassy coal mines. To prevent the gas related mining hazards, effective gas drainage is a pivot technology to reduce the gas content in coal seams. For low permeability coal seams, permeability enhancement is one of the top challenges for enhancing gas drainage efficiency. In the study, a novel methane drainage technology for coal permeability enhancement, namely CO2 gas fracturing (CO2-Frac), has been proposed and investigated in Luan coal mine field. CO2-Frac is achieved by multiple stage directional CO2 gas fracturing with a newly renovated CARDOX system. Through optimization of the CO2-Frac boreholes parallel to face cleats, a complex and high permeability fracture network was generated in CO2-Frac borehole and hence the improvement of methane gas drainage effectiveness. Mine-scale tests of CO2-Frac have been conducted in 5 coal mines in Luan mine field from December 2011 to December 2015. Methane concentrations and flow rates from both CO2-Frac boreholes and adjacent boreholes without CO2-Frac were continuously monitored for evaluating the stimulation efficiency. It was observed that permeability and methane drainage effectiveness in the CO2-Frac boreholes was significantly improved: (1) gas permeability increases up to 20–50 folds; (2) extracted methane concentration increases ∼10 folds ranging from 50 to 90%, compared the concentration of 5–30% in normal boreholes without CO2-Frac; (3) methane rate in a single CO2-Frac hole varies from 140 to 280m3/d with an increase of 10–20 folds, compared the rate of 14–20m3/d in normal boreholes; (4) methane content of the coal seam in drainage area reduced from original 11.7m3/t to 6.5m3/t after 210days of drainage; (5) upgraded methane from CO2-Frac boreholes can be better utilized in air ventilation methane (AVM) power plant. CO2-Frac is confirmed as the best technology to drainage methane in this low permeability coal seams in Luan mine field, and it is not only beneficial on coal mine gas control and safety management but the CMM economic utilization by upgrading drained methane gas concentration.

Time-Dependent Methane Diffusion Behavior in Coal: Measurement and Modeling

In-depth understanding of how methane diffuses in porous media like coal is critical for enhanced coalbed methane recovery and coal seam methane drainage. However, the classic unipore gas diffusion model can only describe methane diffusion behavior in coal at the early time diffusion stage. Describing the whole methane diffusion behavior in coal has not been reasonably addressed in the coalbed methane field. Considering the large surface-to-volume ratio of coal, the authors proposed a time-dependent gas diffusion model to describe the whole diffusion process. This work first proposed a power–law relationship between diffusion coefficient and time according to previous studies of the time-dependent gas diffusion process in porous media. Then, both the analytical solution and its approximation solution for the time-dependent gas diffusion model were derived. Six methane diffusion tests in crushed coal were conducted to validate the proposed model under different pressures (0.5, 1.5, 2.5 MPa) and temperatures (20 and \(30\,{^{\circ }}\hbox {C}\)). Modeling results show that the time-dependent gas diffusion model is superior to the classic unipore gas diffusion model for describing the whole methane diffusion process in coal. Increasing temperature always accelerates methane diffusion in coal; the higher the temperature the larger the diffusion coefficient.

Effect of pore characteristics on coalbed methane adsorption in middle-high rank coals

Gas hazards are still one of the most severe disasters restricting mine safety, and the occurrence of them is heavily dependent on the storage and transportation of methane in coal seams. In order to investigate the influence of pore structure characteristics of middle-high rank coals (V daf < 25 %) on coalbed methane adsorption, six coal samples of different metamorphism were studied with regard to their surface chemical structure and pore morphological features using Fourier transform infrared (FTIR) spectroscopy, low-pressure nitrogen gas adsorption (LP-N2GA) and scanning electron microscopy (SEM), and their coalbed methane adsorption capacities were also tested. Based on the Langmuir equation, the Langmuir volume and Langmuir pressure were obtained to characterize the adsorption capacity, and the impact of structural parameters of coal samples on coalbed methane adsorption was analyzed. The results indicate that the pore shape varies a lot between coal samples, suggesting the significant heterogeneity on coal surface. The micropores (<10 nm) in coal samples are well-developed, and the pore size distributions from adsorption analysis are multi-modal. Pore characteristics in coal samples is affected by coalification to a large extent. The adsorption volume of gas mainly concentrates in micropores, and the adsorption capacities of different coal samples display remarkable difference. The Langmuir volume (V L) is closely related to micropores, but shows little relationship with mesopores, while the Langmuir pressure (P L) is remarkably affected by both micropores and mesopores. The research results are of great importance for the coalbed methane storage and the accurate prediction of gas emission.

Stimulation of commercial coal seam methane production aimed at improving mining technology

The relevance of the current research is due to the urgent need to revise the existing normative bases and procedures involved in intensive development of coal-methane deposits and commercial production of coal seam methane. The article presents the analysis of data on coal production volume and amount of methane emitted into the atmosphere in Kuzbass. There is a need to develop the exploration techniques that would allow implementing pre-mining gas drainage of coal seams and provide the companies with the guidance on coal seam methane drainage in very gassy coal mines. Commercial production of methane should become an integral part of economy and energy balance of the Russian Federation, which, in its turn, would enhance environmental protection due to reducing methane emissions, the largest source of greenhouse effect.

Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams

The methane concentration of the return current will always be enhanced to a certain degree when hydraulic fracturing with bedding drilling is implemented to a gassy coal seam in an underground coal mine. The methane in coal seam is driven out by hydraulic fracturing. Thus, the phenomenon is named as methane driven effect of hydraulic fracturing. After deep-hole hydraulic fracturing at the tunneling face of the gassy coal seam, the coal methane content exhibits a “low-high-low” distribution along excavation direction in the following advancing process, verifying the existence of methane driven caused by hydraulic fracturing in methane-bearing coal seam. Hydraulic fracturing causes the change of pore-water and methane pressure in surrounding coal. The uneven distribution of the pore pressure forms a pore pressure gradient. The free methane migrates from the position of high pore (methane) pressure to the position of low pore (methane) pressure. The methane pressure gradient is the fundamental driving force for methane-driven coal seam hydraulic fracturing. The uneven hydraulic crack propagation and the effect of time (as some processes need time to complete and are not completed instantaneously) will result in uneven methane driven. Therefore, an even hydraulic fracturing technique should be used to avoid the negative effects of methane driven; on the other hand, by taking fully advantage of methane driven, two technologies are presented.

A method for hydrofracture propagation control based on non-uniform pore pressure field

Hydraulic fracturing technology, a technique for increasing productivity applicable in low-permeability oil-gas reservoir, has been used in the extraction of coal seam methane in underground coal mines. However, because of the more complex structure of coal seam compared with that of oil-gas reservoir, the hydrofracture propagation can easily extend to roof-floor rocks, limiting the range of permeability and making damages of roof-floor rocks in subsequent coal mining and support difficulty. How to control the hydrofracture propagation well-aligned in a large area of coal seam has become the key to long-time highly effective extraction of coal seam methane. Firstly, it starts with the perspective of stress field of crack tip, by means of thermal elasticity fracture mechanics theory, to get the stress intensity factor of hydrofracture tip while taking pore pressure into consideration. Next, a laboratory fracturing experiment using sandstone specimens was conducted to study the impact of non-uniform pore pressure on the direction of hydrofracture propagation. Lastly, a numerical simulation software RFPA2D-Flow is adopted to further verify the theoretical and experimental results. The study shows that pore pressure can effectively increase the stress intensity factor of the crack tip, the more pressure of pore, the smaller the needed fluid pressure for hydrofracture propagation. In a large area, affected by the direction and distribution of pore pressure gradient, the hydrofracture will propagate along higher pore pressure area. A method is put forward for controlling hydrofracture propagation in underground coal mines accordingly. Meanwhile, the matching relationship between the space between boreholes and the water injection maintaining pressure and maintaining time are studied together, with methods and steps for calculating key fracture parameters established.

Revealing colonisation and biofilm formation of an adherent coal seam associated microbial community on a coal surface

The discovery that coal seam microbial communities contribute appreciably to coal seam methane (CSM) reserves worldwide has led to an increased interest in the coal seam microbiome. While studies to date have focussed on characterising the microbial communities in a mature state, very little has been reported on the physical niche partitioning and colonisation processes of these communities on coal surfaces. Coal represents a difficult substrate for microbial characterisation using classical techniques due to in its adsorptive nature and recalcitrance to reflectance and fluorescence-based microscopy. This study presents a new technique involving culturing on specially prepared polished coal disks which allows for examination of microbes adherent to the coal surface using both molecular and microscopic approaches. Using this technique we have investigated the colonisation process of the coal surface including evidence for the involvement of a biofilm and successional changes in abundance of several community members during colonisation.

Coal Seam Methane Abatement and Utilization Techniques with Availability and Feasibility Criteria

Coal Seam Methane Abatement and Utilization Techniques with Availability and Feasibility Criteria

Sorption charateristics of methane among various rank coals: impact of moisture

Enhanced coalbed methane (ECBM) in deep coal seams is being actively investigated around the world. Since the in situ coal seams are always saturated with water, methane sorption behavior on coal in the presence of water can help accurately assess the amount of recoverable methane. Thus, methane sorption isotherms have been measured on a high-rank anthracite, a low-volatile bituminous, a middle-volatile bituminous and a high-volatile bituminous coal with the manometric technology at 30 °C under six different moisture contents. The Dubinin–Astakhov (D–A) equation was used to fit the experimental sorption isotherm data. In all cases, the moisturized coals exhibited lower sorption capacity than the corresponding dry materials and moisture has a significant effect on CH4 sorption capacity. The maximum sorption capacity, V 0, displays a linear decline with the moisture content for the Changcun and Malan samples, but it is nonlinear for the other two coal samples. The net heat of CH4 sorption, βE, is also reduced by the presence of water, but varies only slightly between a relatively small span of about 8.8 and 10.0 kJ mol−1 for the dry samples studied, despite the difference in coal rank. In addition, the maximum sorption capacity of CH4 in dry coals presents the typical “U-shape” trend with coal rank. Moisture has a greater impact on the sorption capacity in low-rank coals than that in high-rank coals. The mechanisms responsible for the effect of moisture on CH4 sorption among various rank coals are also presented. The pore-blocking effect is the main influencing factor for high-rank anthracite, whereas, the competition sorption is dominant for low-rank coals.

Coal Seam Methane Abatement and Utilization Techniques with Availability and Feasibility Criteria

Coal Seam Methane Abatement and Utilization Techniques with Availability and Feasibility Criteria

Laboratory characterisation of coal matrix shrinkage, cleat compressibility and the geomechanical properties determining reservoir permeability

This paper presents the results of a laboratory program of work to measure the coal properties required to apply models for the behaviour of the absolute reservoir permeability during gas production. These measurements were made on core samples from the Bowen Basin of Australia, an important area for coal seam methane production, and involved applying an integrated testing methodology. During the testing the pore pressure was increased in a stepwise fashion with gas adsorption equilibration allowed at each pressure step. The gas content of the intact sample was estimated from the gas taken up during equilibration and the sample swelling in response to adsorption measured. After adsorption had equilibrated, the geomechanical properties were determined through axial loading and measurement of the deformation and the permeability measured with respect to confining pressure. These permeability measurements were then used to estimate the cleat compressibility by fitting the Seidle model to the observations. The results from five coal samples are presented. A method is presented for the calculation of the cleat porosity, a difficult property to determine experimentally as it represents the proportion of the porosity involved in Darcy flow. Thus, the presented method uses a property determined from flow measurements; the cleat compressibility. The measured properties are used in the Shi–Durucan model to predict permeability behaviour with pressure drawdown. The results are compared to the field based estimates from the analysis of Mazumder et al. (2012).