The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms...The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms of free gas remains limited.This study identifies structural elements associated with free gas,such as thrust faults,piggyback basins,unconformities,and décollements,through detailed interpretation of newly acquired seismic data.Free gas reservoirs within piggyback basins are located in the folded zone of the accretionary prism,whereas unconformity-type and horizontal sandstone-type free gas reservoirs are identified in undeformed areas.In the folded zone,décollement,thrust faults,and permeable sand layers act as primary migration pathways for free gas,which accumulates in turbidite sands beneath bottom simulating reflectors(BSRs)in piggyback basins.In the undeformed zone,free gas migrates along décollements and thrust faults into horizontal sandstones,where substantial accumulations are found near unconformities below BSRs.The distribution of free gas reservoirs across the study area is extensive and diverse.This study is the first to document unconformity-type and horizontal sandstone-type free gas reservoirs in the undeformed zone,highlighting their considerable resource potential.The findings are of substantial value for oil and gas exploration at the front of the accretionary prism and provide important theoretical and practical insights into natural gas accumulation systems along active continental margins.展开更多
Taking deep coal-rock gas in the Yulin and Daning-Jixian areas of the Ordos Basin,NW China,as the research object,full-diameter coal rock samples with different cleat/fracture development degrees from the Carboniferou...Taking deep coal-rock gas in the Yulin and Daning-Jixian areas of the Ordos Basin,NW China,as the research object,full-diameter coal rock samples with different cleat/fracture development degrees from the Carboniferous Benxi Formation were selected to conduct physical simulation and isotope monitoring experiments of the full-life-cycle depletion development of coal-rock gas.Based on the experimental results,a dual-medium carbon isotope fractionation(CIF)model coupling cleats/fractures and matrix pores was constructed,and an evaluation method for free gas production patterns was established to elucidate the carbon isotope fractionation mechanism and adsorbed/free gas production characteristics during deep coal-rock gas development.The results show that the deep coal-rock gas development process exhibits a three-stage carbon isotope fractionation pattern:“Stable(Ⅰ)→Decrease(Ⅱ)→Increase(Ⅲ)”.A rapid decline in boundary pressure in stageⅢleads to fluctuations in isotope value,characterized by a“rapid decrease followed by continued increase”,with free gas being produced first and long-term supply of adsorbed gas.The CIF model can effectively match measured gas pressure,cumulative gas production,and δ^(13)C_(1) value of produced gas.During the first two stages of isotope fractionation,free gas dominated cumulative production.During the mid-late stages of slow depletion production,the staged pressure control development method can effectively increase the gas recovery.The production of adsorbed gas is primarily controlled by the rock's adsorption capacity and the presence of secondary flow channels.Effectively enhancing the recovery of adsorbed gas during the late stage remains crucial for maintaining stable production and improving the ultimate recovery factor of deep coal-rock gas.展开更多
In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well...In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.展开更多
Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have ...Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have been confirmed by logging,coring,and production tests in the foraminifera-rich silty sediments with complex bottom-simulating reflectors(BSRs).The broad-band processing is conducted on conventional three-dimensional(3D)seismic data to improve the image and detection accuracy of gas hydratebearing layers and delineate the saturation and thickness of gas hydrate-and free gas-bearing sediments.Several geophysical attributes extracted along the base of the gas hydrate stability zone are used to demonstrate the variable distribution and the controlling factors for the differential enrichment of gas hydrate.The inverted gas hydrate saturation at the production zone is over 40% with a thickness of 90 m,showing the interbedded distribution with different boundaries between gas hydrate-and free gas-bearing layers.However,the gas hydrate saturation value at the adjacent canyon is 70%,with 30-m-thick patches and linear features.The lithological and fault controls on gas hydrate and free gas distributions are demonstrated by tracing each gas hydrate-bearing layer.Moreover,the BSR depths based on broad-band reprocessed 3D seismic data not only exhibit variations due to small-scale topographic changes caused by seafloor sedimentation and erosion but also show the upward shift of BSR and the blocky distribution of the coexistence of gas hydrate and free gas in the Pearl River Mouth Basin.展开更多
Deep shale gas(3500-4500 m)will be the important succeeding field for the growth of shale gas production in China.Under the condition of high temperature and high pressure in deep shale gas reservoirs,its gas occurren...Deep shale gas(3500-4500 m)will be the important succeeding field for the growth of shale gas production in China.Under the condition of high temperature and high pressure in deep shale gas reservoirs,its gas occurrence characteristics are markedly different from those of medium and shallow layers.To elucidate the gas occurrence characteristics and controlling factors of deep shales in the Wufeng-Longmaxi Formation,methane adsorption,low-temperature N2,and cO2 adsorption experi-ments were conducted.The results show that in deep shales,the mesopores provide approximately 75%of the total specific surface area(SA)and 90%of the total pore volume(PV).Based on two hypotheses and comparing the theoretical and actual adsorption capacity,it is speculated that methane is adsorbed in deep shale in the form of micropore filling,and free gas is mainly stored in the mesopores.Correlation analysis demonstrated that ToC is the key material constraint for the adsorption capacity of deep shale,and micropore SSA is the key spatial constraint.Other minerals and mesopore parameters have limited effect on the amount of adsorbed gas.Moreover,the free gas content ranges from 2.72 m^(3)/t to 6.20 m^(3)/t,with an average value of 4.60 m^(3)/t,and the free gas content ratio is approximately 58%,suggesting that the deep shale gas reservoirs are dominated by free gas.This ratio may also increase to approximately 70%when considering the formation temperature effect on adsorbed gas.Gas density,porosity,and gas saturation are the main controlling factors of free gas content,resulting in significantly larger free gas content in deep shale than in shallower formations.展开更多
By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of s...By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of shale gas.An improved evaluation method of shale gas content evolution in superimposed basins is proposed.This method incorporates the coupling effect of key geological factors such as temperature,pressure,organic matter abundance,maturity,and pore characteristics on the content and occurrence state of shale gas,as well as the configuration relationship between shale gas generation and storage throughout geological history.Using this approach,the gas evolution histories of the Longmaxi Formation shales in wells N201 and PY1 are reconstructed under varying geological conditions.The Longmaxi Formation shales in these wells are dominated by typeⅠkerogen,with original total organic carbon(TOC_(o))contents of 6.20 wt% and 4.92 wt%,respectively,indicating differences in the initial material basis for gas generation.At the maximum burial depth of approximately 5000 m,the Longmaxi Formation shale in well N201 exhibits a formation pressure coefficient of 2.05,an organic matter maturity of 2.2%,and organic pores accounting for 68%of the total porosity.The gas generation quantity(Q_(g))reaches 19.24 m^(3)/t,while the gas storage capacity(Q_(s))is 4.30 m^(3)/t.The actual total gas content(Q_(a)),constrained by Q_(s),is 4.30 m^(3)/t,with free gas comprising 94%.Following relatively moderate tectonic uplift,the Q_(a) in well N201 decreases to 4.03 m^(3)/t,with free gas accounting for 63%.In contrast,the Longmaxi Formation shale in well PY1 reached a maximum burial depth of 6300 m,associated with a formation pressure coefficient of 1.62,organic matter maturity of 2.5%,and organic pore proportion of 67%.Here,Q_(g) is 16.87 m^(3)/t,and both Q_(s) and Q_(a) are 3.65 m^(3)/t,with free gas accounting for 98%.After intense tectonic uplift,Q_(a) declines to 2.72 m^(3)/t,and the proportion of free gas drops to51%.Finally,a four-stage differential accumulation model of shale gas is established:Slow gas generation and only adsorbed gas occur in stageⅠ,which is primarily controlled by TOC content;both adsorbed gas and free gas present in stageⅡ,with free gas becoming dominant;rapid gas generation and free gas predominance are controlled by temperature and porosity in stageⅢ;and gas adjustment and accumulation are primarily controlled by temperature and pressure in stageⅣ.展开更多
Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some sho...Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some shortcomings because of the low permeability and tightness of shale,complex gas flow behavior of multi-scale gas transport regions and multiple gas transport mechanism superpositions,and complex and variable production regimes of shale gas wells.Recent research has demonstrated the existence of a multi-stage isotope fractionation phenomenon during shale gas production,with the fractionation characteristics of each stage associated with the pore structure,gas in place(GIP),adsorption/desorption,and gas production process.This study presents a new approach for estimating shale gas well production and evaluating the adsorbed/free gas ratio throughout production using isotope fractionation techniques.A reservoir-scale carbon isotope fractionation(CIF)model applicable to the production process of shale gas wells was developed for the first time in this research.In contrast to the traditional model,this model improves production prediction accuracy by simultaneously fitting the gas production rate and δ^(13)C_(1) data and provides a new evaluation method of the adsorbed/free gas ratio during shale gas production.The results indicate that the diffusion and adsorption/desorption properties of rock,bottom-hole flowing pressure(BHP)of gas well,and multi-scale gas transport regions of the reservoir all affect isotope fractionation,with the diffusion and adsorption/desorption parameters of rock having the greatest effect on isotope fractionation being D∗/D,PL,VL,α,and others in that order.We effectively tested the universality of the four-stage isotope fractionation feature and revealed a unique isotope fractionation mechanism caused by the superimposed coupling of multi-scale gas transport regions during shale gas well production.Finally,we applied the established CIF model to a shale gas well in the Sichuan Basin,China,and calculated the estimated ultimate recovery(EUR)of the well to be 3.33×10^(8) m^(3);the adsorbed gas ratio during shale gas production was 1.65%,10.03%,and 23.44%in the first,fifth,and tenth years,respectively.The findings are significant for understanding the isotope fractionation mechanism during natural gas transport in complex systems and for formulating and optimizing unconventional natural gas development strategies.展开更多
Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals th...Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals the fluid characteristics,gas accumulation control factors and accumulation modes in the Upper Paleozoic coal reservoirs.The study indicates findings in two aspects.First,the 1500-1800 m interval represents the critical transition zone between open fluid system in shallow-medium depths and closed fluid system in deep depths.The reservoirs above 1500 m reflect intense water invasion,with discrete pressure gradient distribution,and the presence of methane mixed with varying degrees of secondary biogenic gas,and they generally exhibit high water saturation and adsorbed gas undersaturation.The reservoirs deeper than 1800 m,with extremely low permeability,are self-sealed,and contains closed fluid systems formed jointly by the hydrodynamic lateral blocking and tight caprock confinement.Within these systems,surface runoff infiltration is weak,the degree of secondary fluid transformation is minimal,and the pressure gradient is relatively uniform.The adsorbed gas saturation exceeds 100%in most seams,and the free gas content primarily ranges from 1 m^(3)/t to 8 m^(3)/t(greater than 10 m^(3)/t in some seams).Second,the gas accumulation in deep coals is primarily controlled by coal quality,reservoir-caprock assemblage,and structural position governed storage,wettability and sealing properties,under the constraints of the underground temperature and pressure conditions.High-rank,low-ash yield coals with limestone and mudstone caprocks show superior gas accumulation potential.Positive structural highs and wide and gentle negative structural lows are favorable sites for gas enrichment,while slope belts of fold limbs exhibit relatively lower gas content.This research enhances understanding of gas accumulation mechanisms in coal reservoirs and provides effective parameter reference for precise zone evaluation and innovation of adaptive stimulation technologies for deep resources.展开更多
Through systematic investigation of deep coal-rock gas in the Ordos Basin,NW China,this work analysed the thickness distribution of the entire Upper Paleozoic coal-rock intervals,quantified the resource potential of r...Through systematic investigation of deep coal-rock gas in the Ordos Basin,NW China,this work analysed the thickness distribution of the entire Upper Paleozoic coal-rock intervals,quantified the resource potential of representative areas(a 12000 km2 rectangular block in the eastern Ordos Basin roughly centered on Yulin City),clarified the occurrence characteristics of coal-rock gas,and identified key development indicators for gas wells,thereby defining the direction for iterative optimization of key technologies.(1)The total coal-rock gas in-place of the Upper Paleozoic coal seams 1^(#)-10^(#)in the resource evaluation region is assessed at 5.66×10^(12) m^(3),of which coal seam 8^(#),currently the main target interval,contains about 3.08×10^(12) m^(3),accounting for roughly 54%of the total.(2)Deep coal-rock gas is characterized by a high ratio of free gas.Under the conditions of 2000 m burial depth,6.35%porosity,95%free gas saturation,and 22.13 m^(3)/t total gas content,the free gas content of the reservoir is estimated to be ca.40%of the total gas.(3)Three productivity evaluation models(triangular,convex,concave)are developed for horizontal wells,of which the triangular model can serve as the reference model for predicting the estimated ultimate recovery(EUR)throughout the lifecycle of coal-rock gas wells.Using the triangular model with a 7 m coal thickness,1500 m effective lateral length and 400 m well spacing,the average single-well EUR is determined to be 4621.28×10^(4) m^(3).(4)Development of the coal seam 8^(#)should employ horizontal wells with pressure-controlled production.Meanwhile,it can be further optimized by adopting the cost-effective strategies of Sulige Gas Field in the Ordos Basin,China.(5)To achieve cost-effective development and increase primary recovery factor,key technologies must undergo continuous iteration and upgrading,focusing on accelerating drilling,extending effective lateral lengths,high-intensity reservoir stimulation,and well-pattern optimization.展开更多
A new detection system consisted of a flame ionization detector（FID） and a sulfur chemiluminescence detector（SCD） was developed for sensitive and interference free determination of total sulfur in natural gas by n...A new detection system consisted of a flame ionization detector（FID） and a sulfur chemiluminescence detector（SCD） was developed for sensitive and interference free determination of total sulfur in natural gas by non-separation gas chromatography. In this system, sulfur containing compounds and hydrocarbons were firstly burned in the FID using oxygen rich flame and converted to SO_2, CO_2 and H_2O, respectively. The products from FID were transported into the SCD with hydrogen rich atmosphere wherein only SO_2 could be reduced to SO and reacted with O_3 to produce characteristic chemiluminescence. Therefore, the chemiluminescence of CO found in conventional SCD were eliminated because CO_2 could not be reduced to CO under these conditions. The experimental parameters were systematically investigated. Limit of detection obtained by the proposed system is better than 0.5 mmol/mol for total sulfur and superior to those previously reported. The proposed method not only retains the advantages of the conventional SCD but also provides several unique advantages including no hydrocarbon interference, better stability, and easier calculation. The utility of this technique was demonstrated by the determination of total sulfur in real samples and two certified reference materials（GBW 06332 and GBW（E） 061320）.展开更多
The free electron gas in a uniform magnetic field at low temperature is restudied. The grand partition function previously obtained by Landau＇s quantitative calculation contains three parts, which are all approximate...The free electron gas in a uniform magnetic field at low temperature is restudied. The grand partition function previously obtained by Landau＇s quantitative calculation contains three parts, which are all approximate. An improved calculation is presented, in which two of the three parts are obtained in exact forms. A simple remedy for Landau and Lifshitz＇s qualitative calculation in the textbook is also given, which turns the qualitative result into the same one as obtained by the improved quantitative calculation. The chemical potential is solved approximately and the thermodynamic quantities are caiculated explicitly in both a weak field and a strong field. The thermodynamic quantities in a strong field obtained here contain both non-oscillating and oscillating corrections to the corresponding results derived from Landau＇s grand partition function. In particular, Landau＇s grand partition function is not sufficiently accurate to yield our nonzero results for the specific heat and the entropy. An error in the Laplace-transform method for the problem is corrected. The results previously obtained by this method are also improved.展开更多
Shale needs to contain a sufficient amount of gas to make it viable for exploitation. The continental heterogeneous shale formation in the Yan-chang （YC） area is investigated by firstly measuring the shale gas conte...Shale needs to contain a sufficient amount of gas to make it viable for exploitation. The continental heterogeneous shale formation in the Yan-chang （YC） area is investigated by firstly measuring the shale gas content in a laboratory and then investigating use of a theoretical prediction model. Key factors controlling the shale gas content are determined, and a prediction model for free gas content is established according to the equation of gas state and a new petrophysical volume model. Application of the Langmuir volume constant and pressure constant obtained from results of adsorption isotherms is found to be limited because these constants are greatly affected by experimental temperature and pressures. Therefore, using measurements of adsorption isotherms and thermodynamic theory, the influence of temperature, total organic carbon （TOC）, and mineralogy on Langmuir volume constants and pressure constants are investigated in detail. A prediction model for the Langmuir pressure constant with a correction of temperatures is then established, and a prediction model for the Langmuir volume constant with correction of temperature, TOC, and quartz contents is also proposed. Using these corrected Langmuir constants, application of the Langmuir model determined using experimental adsorption isotherms is extrapolated to reservoir temperature, pressure, and lithological conditions, and a method for the prediction of shale gas content using well logs is established. Finally, this method is successfully applied to predict the shale gas content of the continental shale formation in the YC area, and practical application is shown to deliver good results with high precision.展开更多
In recent years,great breakthroughs have been made in the exploration and development of natural gas in deep coal-rock reservoirs in Junggar,Ordos and other basins in China.In view of the inconsistency between the ind...In recent years,great breakthroughs have been made in the exploration and development of natural gas in deep coal-rock reservoirs in Junggar,Ordos and other basins in China.In view of the inconsistency between the industrial and academic circles on this new type of unconventional natural gas,this paper defines the concept of"coal-rock gas"on the basis of previous studies,and systematically analyzes its characteristics of occurrence state,transport and storage form,differential accumulation,and development law.Coal-rock gas,geologically unlike coalbed methane in the traditional sense,occurs in both free and adsorbed states,with free state in abundance.It is generated and stored in the same set of rocks through short distance migration,occasionally with the accumulation from other sources.Moreover,coal rock develops cleat fractures,and the free gas accumulates differentially.The coal-rock gas reservoirs deeper than 2000 m are high in pressure,temperature,gas content,gas saturation,and free-gas content.In terms of development,similar to shale gas and tight gas,coal-rock gas can be exploited by natural formation energy after the reservoirs connectivity is improved artificially,that is,the adsorbed gas is desorbed due to pressure drop after the high-potential free gas is recovered,so that the free gas and adsorbed gas are produced in succession for a long term without water drainage for pressure drop.According to buried depth,coal rank,pressure coefficient,reserves scale,reserves abundance and gas well production,the classification criteria and reserves/resources estimation method of coal-rock gas are presented.It is preliminarily estimated that the coal-rock gas in place deeper than 2000 m in China exceeds 30×10^(12)m^(3),indicating an important strategic resource for the country.The Ordos,Sichuan,Junggar and Bohai Bay basins are favorable areas for large-scale enrichment of coal-rock gas.The paper summarizes the technical and management challenges and points out the research directions,laying a foundation for the management,exploration,and development of coal-rock gas in China.展开更多
Natural gas hydrates are considered as strategic resources with commercial potential in the 21st century. Obvious BSR characteristics will be shown on seismic profiles, if there exist natural gas hydrates. The AVO met...Natural gas hydrates are considered as strategic resources with commercial potential in the 21st century. Obvious BSR characteristics will be shown on seismic profiles, if there exist natural gas hydrates. The AVO method is one of the methods which can be used to identify and forecast lithologic characteristics and fluid properties by using the relationship between Amplitude and Offset. AVO anomaly is one of the significant signs to check out whether or not there is free gas below the BSR, so it can be used to detect natural gas hydrates from the seismic profile. Considering the geological and geophysical characteristics of the Okinawa Trough and making use of the techniques mentioned above, we can conclude that the conditions there are favorable for the formation and concentration of natural gas hydrates. By analyzing the data collected from the study area, one can discover many different anomalous phenomena on the seismic profile which are related to the existence of natural gas hydrates. Preliminary estimation of the natural gas hydrates in the Okinawa Trough shows that the trough is rich in natural gas hydrates and may become a potential important resources exploration area.展开更多
Free gas saturation is a key parameter for calculating shale gas reserves.The complex conductivity mechanism of shale reservoirs restricts the application of Archie's formula and its extended form for the evaluati...Free gas saturation is a key parameter for calculating shale gas reserves.The complex conductivity mechanism of shale reservoirs restricts the application of Archie's formula and its extended form for the evaluation of free gas saturation.Instead,a number of non-resistivity-based saturation evaluation methods suitable for shale gas reservoirs have been established,including core calibration(TOC method,clay content method),gas porosity cutoff,excavation effect and four-pore modeling.These methods,together with adsorbed phase porosity correction,are used to calculate the free gas saturation.These methods are applied to shale reservoirs of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Sichuan Basin,southwestern China to test their applicability and accuracy.The results,when compared with measured data from core samples,show that the TOC-based core calibration is more accurate in evaluating free gas saturation in the entire shale gas interval,which is of great significance to the calculation of shale gas reserves.展开更多
The Permian Wujiaping Formation(P_(3)w)shale in eastern Sichuan Basin exhibits high gas content.Through total organic carbon(TOC)content determination,mineral composition analysis,N_(2)/CO_(2) adsorption,high-pressure...The Permian Wujiaping Formation(P_(3)w)shale in eastern Sichuan Basin exhibits high gas content.Through total organic carbon(TOC)content determination,mineral composition analysis,N_(2)/CO_(2) adsorption,high-pressure methane adsorption,and scanning electron microscopy experiments,we identified determinants of the high gas content and restored in-situ gas content.Findings demonstrate that the supercritical Dubinin-Astakhov(S-DA)model(based on micropore-filling theory)represents the optimal approach for accurately restoring the absolute adsorption amount of the third member of P_(3)w(P_(3)w^(3))shale within the study region compared to the supercritical Langmuir(S-L)model(based on monolayer adsorption theory)widely used in the assessment of gas content of the Wufeng-Longmaxi shale.The P_(3)w^(3) and Wufeng-Longmaxi shales have similar adsorption capacities at equivalent TOC levels,with the high adsorbed gas content of P_(3)w^(3) attributed to the development of rich organic shale(with a TOC content of 7.68%)in the anoxic reduction environment of the deep marine shelf facies.The high free gas content is due to the abundant siliceous minerals that play an anti-compaction and porepreservation effect during the diagenesis,forming rich pore spaces(porosity of 6.05%).Under the influence of formation temperature and pressure,the in-situ gas content of P_(3)w^(3)shale reservoir gradually increases with burial depth.The P_(3)w^(3) shale gas reservoir with a burial depth of 4300-4400 m mainly exists in the free state,with the ratio of free gas to adsorbed gas approximately 7:3.展开更多
In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Sha...In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Shale Gas Fields as the research object to quantitatively characterize the development characteristics of natural fractures in the Longmaxi Formation shale by means of helium pycnometry,X-ray diffraction(XRD),true density testing and other methods,with the aid of the modified petrophysical model.Then,the development types and genetic mechanisms of natural fractures and their influences on shale gas development are discussed.The following research results are obtained.First,the modified petrophysical model can accurately describe the pore system in the Changning shale with a fitting rate of 0.74.Second,the development of natural fractures in shale is different in various regions.The natural fractures in the Changning Shale Gas Field,controlled by basement thrust faults,decollement layers and internal folds,are locally developed and filled with calcareous,and the average fracture porosity is 0.15%.In the Fuling Shale Gas Field,however,natural fractures,mainly controlled by reverse faults and slippage effect,are commonly more developed and unfilled or semi-filled with siliceous,and the average fracture porosity is 1.30%.Third,under the formation conditions,the opening of natural fractures is different.The natural fractures in the Changning Shale Gas Field are basically closed with weaker flowing ability,while those in the Fuling Shale Gas Field are relatively open with stronger flowing ability.Fourth,the occurrence mode of shale gas is influenced by natural fractures,and it is internally dominated by free gas.The initial gas production of shale gas wells is higher.In conclusion,(1)the regression coefficient is introduced to calculate the actual total organic matter content,which promotes the modified petrophysical model to describe matrix pores and fracture pores more accurately;(2)the development of natural fractures in the shale producing pay of the Sichuan Basin is relatively beneficial to shale gas enrichment and exploitation,but the flowing ability of the natural fractures will be weakened under the original formation conditions.展开更多
The most commonly used marker for gas-hydrates is a bottom simulating reflector or BSR on seismic section.The BSR is not a lithological interface but a physical boundary between the gas-hydrates bearing sediments abov...The most commonly used marker for gas-hydrates is a bottom simulating reflector or BSR on seismic section.The BSR is not a lithological interface but a physical boundary between the gas-hydrates bearing sediments above and free-gas saturated sediments below.From visual inspection of seismic section,it is hard to demarcate the zones of gas-hydrates and free-gas laden sediments.At many places in the world,BSRs have not been observed but gas-hydrates have been recovered by drilling.展开更多
Regarding CO_(2)enhanced shale gas recovery,this work focuses on changes in the multiphase(free/adsorbed)CH_(4)in the process of CO_(2)enhanced shale gas recovery,by utilizing a rigorous numerical model with real geol...Regarding CO_(2)enhanced shale gas recovery,this work focuses on changes in the multiphase(free/adsorbed)CH_(4)in the process of CO_(2)enhanced shale gas recovery,by utilizing a rigorous numerical model with real geological parameters.This work studies nine injection well(IW)and CH_(4)production well(PW)combinations of CO_(2)to determine the influence of IW and PW locations on the dynamic interaction of multiphase CH_(4)during 10000 d of CO_(2)injection.The results indicate that the content of both the adsorbed CH_(4)and free CH_(4)is strongly variable before(and during)the CO_(2)-CH_(4)displacement.In addition,during the simulation process,the proportion of the adsorbed CH_(4)among all extracted CH_(4)phases dynamically increases first and then tends to stabilize at 70%-80%.Moreover,the IW-PWs combinations signifi-cantly affect the outcomes of CO_(2)enhanced shale gas recovery-for both the proportion of adsorbed/free CH_(4)and the recovery efficiency.A longer IW-PW distance enables more adsorbed CH_(4)to be recovered but results in a lower efficiency of shale gas recovery.Basically,a shorter IW-PWs distance helps recover CH_(4)via CO_(2)injection if the IW targets the bottom layer of the Wufeng-Longmaxi shale formation.This numerical work expands the knowl-edge of CO_(2)enhanced gas recovery from depleted shale reservoirs.展开更多
The comprehensive analysis of AC electrical conductivity in magnetite was performed in order to find relations between the formation of polarons,phonons and conduction by a virtual free electron gas.The analysis perfo...The comprehensive analysis of AC electrical conductivity in magnetite was performed in order to find relations between the formation of polarons,phonons and conduction by a virtual free electron gas.The analysis performed here for the first time shows experimental data for the behavior of electrons for magnetite with the scattering time shifted to the GHz region.According to our study,the DC electrical conductivity can be described by the virtual free electron gas model,and high frequency conductivity can be described by the combination of the Drude model for disordered materials and Jonscher's universal power law.The observed peak at the imaginary part of AC conductivity was related to the scattering time of the electron-phonon coupling.This interaction between electrons and thermally formed phonons results in the formation of large polarons,and these are responsible for high frequency conductivity in magnetite.展开更多
基金the National Natural Science Foundation of China(Nos.42076069,41406080)the Laoshan Laboratory Science and Technology Innovation Project(No.LSKJ202203401)the China Geological Survey Project(Nos.DD20190581,DD20160155)。
文摘The Makran Accretionary Prism is one of the largest accretionary prisms in the world and hosts substantial natural gas hydrate resources.However,research on the distribution characteristics and accumulation mechanisms of free gas remains limited.This study identifies structural elements associated with free gas,such as thrust faults,piggyback basins,unconformities,and décollements,through detailed interpretation of newly acquired seismic data.Free gas reservoirs within piggyback basins are located in the folded zone of the accretionary prism,whereas unconformity-type and horizontal sandstone-type free gas reservoirs are identified in undeformed areas.In the folded zone,décollement,thrust faults,and permeable sand layers act as primary migration pathways for free gas,which accumulates in turbidite sands beneath bottom simulating reflectors(BSRs)in piggyback basins.In the undeformed zone,free gas migrates along décollements and thrust faults into horizontal sandstones,where substantial accumulations are found near unconformities below BSRs.The distribution of free gas reservoirs across the study area is extensive and diverse.This study is the first to document unconformity-type and horizontal sandstone-type free gas reservoirs in the undeformed zone,highlighting their considerable resource potential.The findings are of substantial value for oil and gas exploration at the front of the accretionary prism and provide important theoretical and practical insights into natural gas accumulation systems along active continental margins.
基金Youth Fund of National Natural Science Foundation of China(42302170)CNPC Scientific and Technological Innovation Fund(2022DQ02-0104)RIPED Open Project Fund(2024-KFKT-31).
文摘Taking deep coal-rock gas in the Yulin and Daning-Jixian areas of the Ordos Basin,NW China,as the research object,full-diameter coal rock samples with different cleat/fracture development degrees from the Carboniferous Benxi Formation were selected to conduct physical simulation and isotope monitoring experiments of the full-life-cycle depletion development of coal-rock gas.Based on the experimental results,a dual-medium carbon isotope fractionation(CIF)model coupling cleats/fractures and matrix pores was constructed,and an evaluation method for free gas production patterns was established to elucidate the carbon isotope fractionation mechanism and adsorbed/free gas production characteristics during deep coal-rock gas development.The results show that the deep coal-rock gas development process exhibits a three-stage carbon isotope fractionation pattern:“Stable(Ⅰ)→Decrease(Ⅱ)→Increase(Ⅲ)”.A rapid decline in boundary pressure in stageⅢleads to fluctuations in isotope value,characterized by a“rapid decrease followed by continued increase”,with free gas being produced first and long-term supply of adsorbed gas.The CIF model can effectively match measured gas pressure,cumulative gas production,and δ^(13)C_(1) value of produced gas.During the first two stages of isotope fractionation,free gas dominated cumulative production.During the mid-late stages of slow depletion production,the staged pressure control development method can effectively increase the gas recovery.The production of adsorbed gas is primarily controlled by the rock's adsorption capacity and the presence of secondary flow channels.Effectively enhancing the recovery of adsorbed gas during the late stage remains crucial for maintaining stable production and improving the ultimate recovery factor of deep coal-rock gas.
基金This study was financially supported by the National Natural Science Foundation of China(Grant Nos.51704197 and 11872258)。
文摘In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.
基金supported by the State Key Laboratory of Natural Gas Hydrate(No.2022-KFJJ-SHW)the National Natural Science Foundation of China(No.42376058)+2 种基金the International Science&Technology Cooperation Program of China(No.2023YFE0119900)the Hainan Province Key Research and Development Project(No.ZDYF2024GXJS002)the Research Start-Up Funds of Zhufeng Scholars Program.
文摘Gas hydrate drilling expeditions in the Pearl River Mouth Basin,South China Sea,have identified concentrated gas hydrates with variable thickness.Moreover,free gas and the coexistence of gas hydrate and free gas have been confirmed by logging,coring,and production tests in the foraminifera-rich silty sediments with complex bottom-simulating reflectors(BSRs).The broad-band processing is conducted on conventional three-dimensional(3D)seismic data to improve the image and detection accuracy of gas hydratebearing layers and delineate the saturation and thickness of gas hydrate-and free gas-bearing sediments.Several geophysical attributes extracted along the base of the gas hydrate stability zone are used to demonstrate the variable distribution and the controlling factors for the differential enrichment of gas hydrate.The inverted gas hydrate saturation at the production zone is over 40% with a thickness of 90 m,showing the interbedded distribution with different boundaries between gas hydrate-and free gas-bearing layers.However,the gas hydrate saturation value at the adjacent canyon is 70%,with 30-m-thick patches and linear features.The lithological and fault controls on gas hydrate and free gas distributions are demonstrated by tracing each gas hydrate-bearing layer.Moreover,the BSR depths based on broad-band reprocessed 3D seismic data not only exhibit variations due to small-scale topographic changes caused by seafloor sedimentation and erosion but also show the upward shift of BSR and the blocky distribution of the coexistence of gas hydrate and free gas in the Pearl River Mouth Basin.
基金funded by a PetroChina Basic Technology Research Project(No.2021DJ1905).
文摘Deep shale gas(3500-4500 m)will be the important succeeding field for the growth of shale gas production in China.Under the condition of high temperature and high pressure in deep shale gas reservoirs,its gas occurrence characteristics are markedly different from those of medium and shallow layers.To elucidate the gas occurrence characteristics and controlling factors of deep shales in the Wufeng-Longmaxi Formation,methane adsorption,low-temperature N2,and cO2 adsorption experi-ments were conducted.The results show that in deep shales,the mesopores provide approximately 75%of the total specific surface area(SA)and 90%of the total pore volume(PV).Based on two hypotheses and comparing the theoretical and actual adsorption capacity,it is speculated that methane is adsorbed in deep shale in the form of micropore filling,and free gas is mainly stored in the mesopores.Correlation analysis demonstrated that ToC is the key material constraint for the adsorption capacity of deep shale,and micropore SSA is the key spatial constraint.Other minerals and mesopore parameters have limited effect on the amount of adsorbed gas.Moreover,the free gas content ranges from 2.72 m^(3)/t to 6.20 m^(3)/t,with an average value of 4.60 m^(3)/t,and the free gas content ratio is approximately 58%,suggesting that the deep shale gas reservoirs are dominated by free gas.This ratio may also increase to approximately 70%when considering the formation temperature effect on adsorbed gas.Gas density,porosity,and gas saturation are the main controlling factors of free gas content,resulting in significantly larger free gas content in deep shale than in shallower formations.
基金funded by the Sinopec Science and Technology Project(No.P23132)the AAPG Foundation Grants-inAid Program(No.18644937)。
文摘By investigating the evolution of shale gas generation,storage,adjustment and accumulation under different structural settings in superimposed basins,this study elucidates the differential accumulation mechanisms of shale gas.An improved evaluation method of shale gas content evolution in superimposed basins is proposed.This method incorporates the coupling effect of key geological factors such as temperature,pressure,organic matter abundance,maturity,and pore characteristics on the content and occurrence state of shale gas,as well as the configuration relationship between shale gas generation and storage throughout geological history.Using this approach,the gas evolution histories of the Longmaxi Formation shales in wells N201 and PY1 are reconstructed under varying geological conditions.The Longmaxi Formation shales in these wells are dominated by typeⅠkerogen,with original total organic carbon(TOC_(o))contents of 6.20 wt% and 4.92 wt%,respectively,indicating differences in the initial material basis for gas generation.At the maximum burial depth of approximately 5000 m,the Longmaxi Formation shale in well N201 exhibits a formation pressure coefficient of 2.05,an organic matter maturity of 2.2%,and organic pores accounting for 68%of the total porosity.The gas generation quantity(Q_(g))reaches 19.24 m^(3)/t,while the gas storage capacity(Q_(s))is 4.30 m^(3)/t.The actual total gas content(Q_(a)),constrained by Q_(s),is 4.30 m^(3)/t,with free gas comprising 94%.Following relatively moderate tectonic uplift,the Q_(a) in well N201 decreases to 4.03 m^(3)/t,with free gas accounting for 63%.In contrast,the Longmaxi Formation shale in well PY1 reached a maximum burial depth of 6300 m,associated with a formation pressure coefficient of 1.62,organic matter maturity of 2.5%,and organic pore proportion of 67%.Here,Q_(g) is 16.87 m^(3)/t,and both Q_(s) and Q_(a) are 3.65 m^(3)/t,with free gas accounting for 98%.After intense tectonic uplift,Q_(a) declines to 2.72 m^(3)/t,and the proportion of free gas drops to51%.Finally,a four-stage differential accumulation model of shale gas is established:Slow gas generation and only adsorbed gas occur in stageⅠ,which is primarily controlled by TOC content;both adsorbed gas and free gas present in stageⅡ,with free gas becoming dominant;rapid gas generation and free gas predominance are controlled by temperature and porosity in stageⅢ;and gas adjustment and accumulation are primarily controlled by temperature and pressure in stageⅣ.
基金supported by the Natural Science Foundation of China(Grant No.42302170)National Postdoctoral Innovative Talent Support Program(Grant No.BX20220062)+3 种基金CNPC Innovation Found(Grant No.2022DQ02-0104)National Science Foundation of Heilongjiang Province of China(Grant No.YQ2023D001)Postdoctoral Science Foundation of Heilongjiang Province of China(Grant No.LBH-Z22091)the Natural Science Foundation of Shandong Province(Grant No.ZR2022YQ30).
文摘Prediction of production decline and evaluation of the adsorbed/free gas ratio are critical for determining the lifespan and production status of shale gas wells.Traditional production prediction methods have some shortcomings because of the low permeability and tightness of shale,complex gas flow behavior of multi-scale gas transport regions and multiple gas transport mechanism superpositions,and complex and variable production regimes of shale gas wells.Recent research has demonstrated the existence of a multi-stage isotope fractionation phenomenon during shale gas production,with the fractionation characteristics of each stage associated with the pore structure,gas in place(GIP),adsorption/desorption,and gas production process.This study presents a new approach for estimating shale gas well production and evaluating the adsorbed/free gas ratio throughout production using isotope fractionation techniques.A reservoir-scale carbon isotope fractionation(CIF)model applicable to the production process of shale gas wells was developed for the first time in this research.In contrast to the traditional model,this model improves production prediction accuracy by simultaneously fitting the gas production rate and δ^(13)C_(1) data and provides a new evaluation method of the adsorbed/free gas ratio during shale gas production.The results indicate that the diffusion and adsorption/desorption properties of rock,bottom-hole flowing pressure(BHP)of gas well,and multi-scale gas transport regions of the reservoir all affect isotope fractionation,with the diffusion and adsorption/desorption parameters of rock having the greatest effect on isotope fractionation being D∗/D,PL,VL,α,and others in that order.We effectively tested the universality of the four-stage isotope fractionation feature and revealed a unique isotope fractionation mechanism caused by the superimposed coupling of multi-scale gas transport regions during shale gas well production.Finally,we applied the established CIF model to a shale gas well in the Sichuan Basin,China,and calculated the estimated ultimate recovery(EUR)of the well to be 3.33×10^(8) m^(3);the adsorbed gas ratio during shale gas production was 1.65%,10.03%,and 23.44%in the first,fifth,and tenth years,respectively.The findings are significant for understanding the isotope fractionation mechanism during natural gas transport in complex systems and for formulating and optimizing unconventional natural gas development strategies.
基金Supported by the National Natural Science Foundation of China(42130802,42272200)CNPC Science and Technology Major Project(2023ZZ18)+1 种基金PetroChina Changqing Oilfield Major Science and Technology Project(2023DZZ01)Technology Project of PetroChina Coalbed Methane Company Limited(2023-KJ-18)。
文摘Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals the fluid characteristics,gas accumulation control factors and accumulation modes in the Upper Paleozoic coal reservoirs.The study indicates findings in two aspects.First,the 1500-1800 m interval represents the critical transition zone between open fluid system in shallow-medium depths and closed fluid system in deep depths.The reservoirs above 1500 m reflect intense water invasion,with discrete pressure gradient distribution,and the presence of methane mixed with varying degrees of secondary biogenic gas,and they generally exhibit high water saturation and adsorbed gas undersaturation.The reservoirs deeper than 1800 m,with extremely low permeability,are self-sealed,and contains closed fluid systems formed jointly by the hydrodynamic lateral blocking and tight caprock confinement.Within these systems,surface runoff infiltration is weak,the degree of secondary fluid transformation is minimal,and the pressure gradient is relatively uniform.The adsorbed gas saturation exceeds 100%in most seams,and the free gas content primarily ranges from 1 m^(3)/t to 8 m^(3)/t(greater than 10 m^(3)/t in some seams).Second,the gas accumulation in deep coals is primarily controlled by coal quality,reservoir-caprock assemblage,and structural position governed storage,wettability and sealing properties,under the constraints of the underground temperature and pressure conditions.High-rank,low-ash yield coals with limestone and mudstone caprocks show superior gas accumulation potential.Positive structural highs and wide and gentle negative structural lows are favorable sites for gas enrichment,while slope belts of fold limbs exhibit relatively lower gas content.This research enhances understanding of gas accumulation mechanisms in coal reservoirs and provides effective parameter reference for precise zone evaluation and innovation of adaptive stimulation technologies for deep resources.
基金Supported by the Scientific Research and Technology Development Project of PetroChina Company Limited(2023YQX103)Scientific Research and Technology Development Project of China National Petroleum Corporation(2024DJ86).
文摘Through systematic investigation of deep coal-rock gas in the Ordos Basin,NW China,this work analysed the thickness distribution of the entire Upper Paleozoic coal-rock intervals,quantified the resource potential of representative areas(a 12000 km2 rectangular block in the eastern Ordos Basin roughly centered on Yulin City),clarified the occurrence characteristics of coal-rock gas,and identified key development indicators for gas wells,thereby defining the direction for iterative optimization of key technologies.(1)The total coal-rock gas in-place of the Upper Paleozoic coal seams 1^(#)-10^(#)in the resource evaluation region is assessed at 5.66×10^(12) m^(3),of which coal seam 8^(#),currently the main target interval,contains about 3.08×10^(12) m^(3),accounting for roughly 54%of the total.(2)Deep coal-rock gas is characterized by a high ratio of free gas.Under the conditions of 2000 m burial depth,6.35%porosity,95%free gas saturation,and 22.13 m^(3)/t total gas content,the free gas content of the reservoir is estimated to be ca.40%of the total gas.(3)Three productivity evaluation models(triangular,convex,concave)are developed for horizontal wells,of which the triangular model can serve as the reference model for predicting the estimated ultimate recovery(EUR)throughout the lifecycle of coal-rock gas wells.Using the triangular model with a 7 m coal thickness,1500 m effective lateral length and 400 m well spacing,the average single-well EUR is determined to be 4621.28×10^(4) m^(3).(4)Development of the coal seam 8^(#)should employ horizontal wells with pressure-controlled production.Meanwhile,it can be further optimized by adopting the cost-effective strategies of Sulige Gas Field in the Ordos Basin,China.(5)To achieve cost-effective development and increase primary recovery factor,key technologies must undergo continuous iteration and upgrading,focusing on accelerating drilling,extending effective lateral lengths,high-intensity reservoir stimulation,and well-pattern optimization.
基金the National Science and Technology Supporting Plan(No.2013BAK12B04)for financial support
文摘A new detection system consisted of a flame ionization detector（FID） and a sulfur chemiluminescence detector（SCD） was developed for sensitive and interference free determination of total sulfur in natural gas by non-separation gas chromatography. In this system, sulfur containing compounds and hydrocarbons were firstly burned in the FID using oxygen rich flame and converted to SO_2, CO_2 and H_2O, respectively. The products from FID were transported into the SCD with hydrogen rich atmosphere wherein only SO_2 could be reduced to SO and reacted with O_3 to produce characteristic chemiluminescence. Therefore, the chemiluminescence of CO found in conventional SCD were eliminated because CO_2 could not be reduced to CO under these conditions. The experimental parameters were systematically investigated. Limit of detection obtained by the proposed system is better than 0.5 mmol/mol for total sulfur and superior to those previously reported. The proposed method not only retains the advantages of the conventional SCD but also provides several unique advantages including no hydrocarbon interference, better stability, and easier calculation. The utility of this technique was demonstrated by the determination of total sulfur in real samples and two certified reference materials（GBW 06332 and GBW（E） 061320）.
基金Supported by the National Natural Science Foundation of China under Grant No.10675174
文摘The free electron gas in a uniform magnetic field at low temperature is restudied. The grand partition function previously obtained by Landau＇s quantitative calculation contains three parts, which are all approximate. An improved calculation is presented, in which two of the three parts are obtained in exact forms. A simple remedy for Landau and Lifshitz＇s qualitative calculation in the textbook is also given, which turns the qualitative result into the same one as obtained by the improved quantitative calculation. The chemical potential is solved approximately and the thermodynamic quantities are caiculated explicitly in both a weak field and a strong field. The thermodynamic quantities in a strong field obtained here contain both non-oscillating and oscillating corrections to the corresponding results derived from Landau＇s grand partition function. In particular, Landau＇s grand partition function is not sufficiently accurate to yield our nonzero results for the specific heat and the entropy. An error in the Laplace-transform method for the problem is corrected. The results previously obtained by this method are also improved.
基金sponsored by National Natural Science Foundation(Project number:41274136)
文摘Shale needs to contain a sufficient amount of gas to make it viable for exploitation. The continental heterogeneous shale formation in the Yan-chang （YC） area is investigated by firstly measuring the shale gas content in a laboratory and then investigating use of a theoretical prediction model. Key factors controlling the shale gas content are determined, and a prediction model for free gas content is established according to the equation of gas state and a new petrophysical volume model. Application of the Langmuir volume constant and pressure constant obtained from results of adsorption isotherms is found to be limited because these constants are greatly affected by experimental temperature and pressures. Therefore, using measurements of adsorption isotherms and thermodynamic theory, the influence of temperature, total organic carbon （TOC）, and mineralogy on Langmuir volume constants and pressure constants are investigated in detail. A prediction model for the Langmuir pressure constant with a correction of temperatures is then established, and a prediction model for the Langmuir volume constant with correction of temperature, TOC, and quartz contents is also proposed. Using these corrected Langmuir constants, application of the Langmuir model determined using experimental adsorption isotherms is extrapolated to reservoir temperature, pressure, and lithological conditions, and a method for the prediction of shale gas content using well logs is established. Finally, this method is successfully applied to predict the shale gas content of the continental shale formation in the YC area, and practical application is shown to deliver good results with high precision.
基金Supported by the Prospective and Basic Research Project of PetroChina(2021DJ23)。
文摘In recent years,great breakthroughs have been made in the exploration and development of natural gas in deep coal-rock reservoirs in Junggar,Ordos and other basins in China.In view of the inconsistency between the industrial and academic circles on this new type of unconventional natural gas,this paper defines the concept of"coal-rock gas"on the basis of previous studies,and systematically analyzes its characteristics of occurrence state,transport and storage form,differential accumulation,and development law.Coal-rock gas,geologically unlike coalbed methane in the traditional sense,occurs in both free and adsorbed states,with free state in abundance.It is generated and stored in the same set of rocks through short distance migration,occasionally with the accumulation from other sources.Moreover,coal rock develops cleat fractures,and the free gas accumulates differentially.The coal-rock gas reservoirs deeper than 2000 m are high in pressure,temperature,gas content,gas saturation,and free-gas content.In terms of development,similar to shale gas and tight gas,coal-rock gas can be exploited by natural formation energy after the reservoirs connectivity is improved artificially,that is,the adsorbed gas is desorbed due to pressure drop after the high-potential free gas is recovered,so that the free gas and adsorbed gas are produced in succession for a long term without water drainage for pressure drop.According to buried depth,coal rank,pressure coefficient,reserves scale,reserves abundance and gas well production,the classification criteria and reserves/resources estimation method of coal-rock gas are presented.It is preliminarily estimated that the coal-rock gas in place deeper than 2000 m in China exceeds 30×10^(12)m^(3),indicating an important strategic resource for the country.The Ordos,Sichuan,Junggar and Bohai Bay basins are favorable areas for large-scale enrichment of coal-rock gas.The paper summarizes the technical and management challenges and points out the research directions,laying a foundation for the management,exploration,and development of coal-rock gas in China.
基金supported by the National High Technology Research and Development (863) Program (Grant No.2006AA09Z339)the Natural Science Foundation of Shandong, China (Grant No. Y2006E09)
文摘Natural gas hydrates are considered as strategic resources with commercial potential in the 21st century. Obvious BSR characteristics will be shown on seismic profiles, if there exist natural gas hydrates. The AVO method is one of the methods which can be used to identify and forecast lithologic characteristics and fluid properties by using the relationship between Amplitude and Offset. AVO anomaly is one of the significant signs to check out whether or not there is free gas below the BSR, so it can be used to detect natural gas hydrates from the seismic profile. Considering the geological and geophysical characteristics of the Okinawa Trough and making use of the techniques mentioned above, we can conclude that the conditions there are favorable for the formation and concentration of natural gas hydrates. By analyzing the data collected from the study area, one can discover many different anomalous phenomena on the seismic profile which are related to the existence of natural gas hydrates. Preliminary estimation of the natural gas hydrates in the Okinawa Trough shows that the trough is rich in natural gas hydrates and may become a potential important resources exploration area.
文摘Free gas saturation is a key parameter for calculating shale gas reserves.The complex conductivity mechanism of shale reservoirs restricts the application of Archie's formula and its extended form for the evaluation of free gas saturation.Instead,a number of non-resistivity-based saturation evaluation methods suitable for shale gas reservoirs have been established,including core calibration(TOC method,clay content method),gas porosity cutoff,excavation effect and four-pore modeling.These methods,together with adsorbed phase porosity correction,are used to calculate the free gas saturation.These methods are applied to shale reservoirs of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the Sichuan Basin,southwestern China to test their applicability and accuracy.The results,when compared with measured data from core samples,show that the TOC-based core calibration is more accurate in evaluating free gas saturation in the entire shale gas interval,which is of great significance to the calculation of shale gas reserves.
基金supported by the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(No.2024CXJB05)the Natural Science Foundation of Sichuan Province of China(No.2025ZNSFSC0309)。
文摘The Permian Wujiaping Formation(P_(3)w)shale in eastern Sichuan Basin exhibits high gas content.Through total organic carbon(TOC)content determination,mineral composition analysis,N_(2)/CO_(2) adsorption,high-pressure methane adsorption,and scanning electron microscopy experiments,we identified determinants of the high gas content and restored in-situ gas content.Findings demonstrate that the supercritical Dubinin-Astakhov(S-DA)model(based on micropore-filling theory)represents the optimal approach for accurately restoring the absolute adsorption amount of the third member of P_(3)w(P_(3)w^(3))shale within the study region compared to the supercritical Langmuir(S-L)model(based on monolayer adsorption theory)widely used in the assessment of gas content of the Wufeng-Longmaxi shale.The P_(3)w^(3) and Wufeng-Longmaxi shales have similar adsorption capacities at equivalent TOC levels,with the high adsorbed gas content of P_(3)w^(3) attributed to the development of rich organic shale(with a TOC content of 7.68%)in the anoxic reduction environment of the deep marine shelf facies.The high free gas content is due to the abundant siliceous minerals that play an anti-compaction and porepreservation effect during the diagenesis,forming rich pore spaces(porosity of 6.05%).Under the influence of formation temperature and pressure,the in-situ gas content of P_(3)w^(3)shale reservoir gradually increases with burial depth.The P_(3)w^(3) shale gas reservoir with a burial depth of 4300-4400 m mainly exists in the free state,with the ratio of free gas to adsorbed gas approximately 7:3.
基金Project supported by the National Major Science and Technology Project“Formation and Enrichment Conditions of Shale Gas in the Sichuan Basin and Its Surrounding Areas,Technologies for Selecting Regions,Evaluation and Applications”(No.:2017ZX05035)。
文摘In order to provide technical support for the shale gas exploration and development in the Lower Silurian Longmaxi Formation of the Sichuan Basin,this paper takes the Longmaxi Formation in the Changning and Fuling Shale Gas Fields as the research object to quantitatively characterize the development characteristics of natural fractures in the Longmaxi Formation shale by means of helium pycnometry,X-ray diffraction(XRD),true density testing and other methods,with the aid of the modified petrophysical model.Then,the development types and genetic mechanisms of natural fractures and their influences on shale gas development are discussed.The following research results are obtained.First,the modified petrophysical model can accurately describe the pore system in the Changning shale with a fitting rate of 0.74.Second,the development of natural fractures in shale is different in various regions.The natural fractures in the Changning Shale Gas Field,controlled by basement thrust faults,decollement layers and internal folds,are locally developed and filled with calcareous,and the average fracture porosity is 0.15%.In the Fuling Shale Gas Field,however,natural fractures,mainly controlled by reverse faults and slippage effect,are commonly more developed and unfilled or semi-filled with siliceous,and the average fracture porosity is 1.30%.Third,under the formation conditions,the opening of natural fractures is different.The natural fractures in the Changning Shale Gas Field are basically closed with weaker flowing ability,while those in the Fuling Shale Gas Field are relatively open with stronger flowing ability.Fourth,the occurrence mode of shale gas is influenced by natural fractures,and it is internally dominated by free gas.The initial gas production of shale gas wells is higher.In conclusion,(1)the regression coefficient is introduced to calculate the actual total organic matter content,which promotes the modified petrophysical model to describe matrix pores and fracture pores more accurately;(2)the development of natural fractures in the shale producing pay of the Sichuan Basin is relatively beneficial to shale gas enrichment and exploitation,but the flowing ability of the natural fractures will be weakened under the original formation conditions.
文摘The most commonly used marker for gas-hydrates is a bottom simulating reflector or BSR on seismic section.The BSR is not a lithological interface but a physical boundary between the gas-hydrates bearing sediments above and free-gas saturated sediments below.From visual inspection of seismic section,it is hard to demarcate the zones of gas-hydrates and free-gas laden sediments.At many places in the world,BSRs have not been observed but gas-hydrates have been recovered by drilling.
基金supported by the Project funded by China Postdoctoral Science Foundation(No.2020M683253)the Key Laboratory of Shale Gas Exploration,Ministry of Natural Resources(No.KLSGE-MLR-202003)the National Natural Science Foundation of China(Grant No.51704197).
文摘Regarding CO_(2)enhanced shale gas recovery,this work focuses on changes in the multiphase(free/adsorbed)CH_(4)in the process of CO_(2)enhanced shale gas recovery,by utilizing a rigorous numerical model with real geological parameters.This work studies nine injection well(IW)and CH_(4)production well(PW)combinations of CO_(2)to determine the influence of IW and PW locations on the dynamic interaction of multiphase CH_(4)during 10000 d of CO_(2)injection.The results indicate that the content of both the adsorbed CH_(4)and free CH_(4)is strongly variable before(and during)the CO_(2)-CH_(4)displacement.In addition,during the simulation process,the proportion of the adsorbed CH_(4)among all extracted CH_(4)phases dynamically increases first and then tends to stabilize at 70%-80%.Moreover,the IW-PWs combinations signifi-cantly affect the outcomes of CO_(2)enhanced shale gas recovery-for both the proportion of adsorbed/free CH_(4)and the recovery efficiency.A longer IW-PW distance enables more adsorbed CH_(4)to be recovered but results in a lower efficiency of shale gas recovery.Basically,a shorter IW-PWs distance helps recover CH_(4)via CO_(2)injection if the IW targets the bottom layer of the Wufeng-Longmaxi shale formation.This numerical work expands the knowl-edge of CO_(2)enhanced gas recovery from depleted shale reservoirs.
基金supported by the Polish Ministry of Science and Higher Education[grant number 0220/DIA/2018/470]the National Science Center,Poland[grant number 2016/23/B/ST8/03405].
文摘The comprehensive analysis of AC electrical conductivity in magnetite was performed in order to find relations between the formation of polarons,phonons and conduction by a virtual free electron gas.The analysis performed here for the first time shows experimental data for the behavior of electrons for magnetite with the scattering time shifted to the GHz region.According to our study,the DC electrical conductivity can be described by the virtual free electron gas model,and high frequency conductivity can be described by the combination of the Drude model for disordered materials and Jonscher's universal power law.The observed peak at the imaginary part of AC conductivity was related to the scattering time of the electron-phonon coupling.This interaction between electrons and thermally formed phonons results in the formation of large polarons,and these are responsible for high frequency conductivity in magnetite.
