A hybrid physics-informed data-driven neural network for CO_(2) storage in depleted shale reservoirs

To reduce CO_(2) emissions in response to global climate change,shale reservoirs could be ideal candidates for long-term carbon geo-sequestration involving multi-scale transport processes.However,most current CO_(2) sequestration models do not adequately consider multiple transport mechanisms.Moreover,the evaluation of CO_(2) storage processes usually involves laborious and time-consuming numerical simulations unsuitable for practical prediction and decision-making.In this paper,an integrated model involving gas diffusion,adsorption,dissolution,slip flow,and Darcy flow is proposed to accurately characterize CO_(2) storage in depleted shale reservoirs,supporting the establishment of a training database.On this basis,a hybrid physics-informed data-driven neural network(HPDNN)is developed as a deep learning surrogate for prediction and inversion.By incorporating multiple sources of scientific knowledge,the HPDNN can be configured with limited simulation resources,significantly accelerating the forward and inversion processes.Furthermore,the HPDNN can more intelligently predict injection performance,precisely perform reservoir parameter inversion,and reasonably evaluate the CO_(2) storage capacity under complicated scenarios.The validation and test results demonstrate that the HPDNN can ensure high accuracy and strong robustness across an extensive applicability range when dealing with field data with multiple noise sources.This study has tremendous potential to replace traditional modeling tools for predicting and making decisions about CO_(2) storage projects in depleted shale reservoirs.

A two-phase type-curve method with multiscale fluid transport mechanisms in hydraulically fractured shale reservoirs

The quantitative understanding of hydraulic fracture(HF)properties guides accurate production forecasts and reserve estimation.Type curve is a powerful technique to characterize HF and reservoir properties from flowback and long-term production data.However,two-phase flow of water and hydrocarbon after an HF stimulation together with the complex transport mechanisms in shale nanopores exacerbate the nonlinearity of the transport equation,causing errors in type-curve analysis.Accordingly,we propose a new two-phase type-curve method to estimate HF properties,such as HF volume and permeability of fracture,through the analysis of flowback data of multi-fractured shale wells.The proposed type curve is based on a semianalytical solution that couples the two-phase flow from the matrix with the flow in HF by incorporating matrix influx,slippage effect,stress dependence,and the spatial variation of fluid properties in inorganic and organic pores.For the first time,multiple fluid transport mechanisms are considered into two-phase type-curve analysis for shale reservoirs.We analyze the flowback data from a multi-fractured horizontal well in a shale gas reservoir to verify the field application of the proposed method.The results show that the fracture properties calculated by the type-curve method are in good agreement with the long-time production data.

Pore-Fracture Distribution Heterogeneity of Shale Reservoirs Determined by using HPMI and LPN_(2 )GA Tests

The compressibility of shale matrix reflects the effects of reservoir lithology, material composition, pore structure and tectonic deformation. It is important to understand the factors that influence shale matrix compressibility(SMC) and their effects on pore size distribution(PSD) heterogeneity in order to evaluate the properties of unconventional reservoirs.In this study, the volumes of pores whose diameters were in the range 6–100 nm were corrected for SMC for 17 shale samples from basins in China using high-pressure mercury intrusion and low-temperature nitrogen gas adsorption analyses,in order to investigate the factors influencing the SMC values. In addition, the variations in fractal dimensions before and after pore volume correction were determined, using single and multifractal models to explain the effects of SMC on PSD heterogeneity. In this process, the applicability of each fractal model for characterizing PSD heterogeneity was determined using statistical analyses. The Menger and Sierpinski single fractal models, the thermodynamic fractal model and a multifractal model were all used in this study. The results showed the following. The matrix compression restricts the segmentation of the fractal dimension curves for the single fractal Menger and Sierpinski models, which leads to a uniformity of PSD heterogeneity for different pore diameters. However, matrix compression has only a weak influence on the results calculated using a thermodynamic model. The SMC clearly affects the multifractal value variations, showing that the fractal dimension values of shale samples under matrix compression are small. Overall PSD heterogeneity becomes small for pores with diameters below 100 nm and the SMC primarily affects the PSD heterogeneity of higher pore volume areas. The comparison of fractal curves before and after correction and the variance analysis indicate that the thermodynamic model is applicable to quantitatively characterize PSD heterogeneity of shale collected from this sampling area. The results show that PSD heterogeneity increases gradually as micro-pore volumes increase.

Simulation of methane adsorption in diverse organic pores in shale reservoirs with multi-period geological evolution

In shale reservoirs,the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane.However,in the process of thermal evolution,the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied.In this study,the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin,China.The results show that the characteristics of pore structure will affect the methane adsorption characteristics.The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores.The groove space inside the pore will change the density distribution of methane molecules in the pore,greatly improve the adsorption capacity of the pore,and increase the pressure sensitivity of the adsorption process.Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size,all pores have the strongest methane adsorption capacity when the pore size is about 2 nm.In addition,the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics.The pore adsorption capacity first increases and then decreases with the increase of pressure,and increases with the increase of temperature.In the early stage of thermal evolution,pore adsorption capacity is strong and pressure sensitivity is weak;while in the late stage,it is on the contrary.

Acid-base alternation diagenesis and its influence on shale reservoirs in the Permian Lucaogou Formation, Jimusar Sag, Junggar Basin, NW China

The diagenesis and diagenetic facies of shale reservoirs in Lucaogou Formation of Jimusar Sag were studied by means of microscopic observation and identification of ordinary thin sections and cast thin sections,X-ray diffraction,scanning electron microscope and electron probe tests.The results show that alkaline and acidic diagenetic processes occurred alternately during the deposition of Permian Lucaogou Formation in Jimusar Sag.The evolution of porosity in the shale reservoirs was influenced by compaction and alternate alkaline and acidic diagenetic processes jointly,and has gone through three stages,namely,stage of porosity reduction and increase caused by alkaline compaction,stage of porosity increase caused by acid dissolution,and stage of porosity increase and reduction caused by alkaline dissolution.Correspondingly,three secondary pore zones developed in Lucaogou Formation.The shale reservoirs are divided into three diagenetic facies:tuff residual intergranular pore-dissolution pore facies,tuff organic micrite dolomite mixed pore facies,and micrite alga-dolomite intercrystalline pore facies.With wide distribution,good pore structure and high oil content,the first two facies are diagenetic facies of favorable reservoirs in Lucaogou Formation.The research results provide a basis for better understanding and exploration and development of the Lucaogou Formation shale reservoirs.

Numerical simulation of hydraulic fracture propagation in laminated shale reservoirs

The main area of the Jiaoshiba anticline of the Fuling shale gas field was taken as the research object,laboratory rock mechanical experiments and direct shear experiments were conducted to clarify the mechanical anisotropy characteristics and parameters of rock samples with rich beddings.Based on the experimental results,a 3D fracture propagation model of the target reservoir taking mechanical anisotropy,weak bedding plane and vertical stress difference into account was established by the discrete element method to analyze distribution patterns of hydraulic fractures under different bedding densities,mechanical properties,and fracturing engineering parameters(including perforation clusters,injection rates and fracturing fluid viscosity).The research results show that considering the influence of the weak bedding plane and longitudinal stress difference,the interlayer stress difference 3–4 MPa in the study area can control the fracture height within the zone of stress barrier,and the fracture height is less than 40 m.If the influence of the weak bedding plane is not considered,the simulation result of fracture height is obviously higher.Although the opening of high-density bedding fractures increases the complexity of hydraulic fractures,it significantly limited the propagation of fracture height.By reducing the number of clusters,increasing the injection rate,and increasing the volume and proportion of high-viscosity fracturing fluid in the pad stage,the restriction on fracture height due to the bedding plane and vertical stress difference can be reduced,and the longitudinal propagation of fractures can be promoted.The fracture propagation model was used to simulate one stage of Well A in Fuling shale gas field,and the simulation results were consistent with the micro-seismic monitoring results.

Microscopic pore-fracture configuration and gas-filled mechanism of shale reservoirs in the western Chongqing area,Sichuan Basin,China

Taking the Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation shale reservoirs in western Chongqing area as the study target,the argon ion polishing scanning electron microscope and nuclear magnetic resonance(NMR)experiments of different saturated wetting media were carried out.Based on the image processing technology and the results of gas desorption,the pore-fracture configuration of the shale reservoirs and its influence on gas-filled mechanism were analyzed.(1)The reservoir space includes organic pores,inorganic pores and micro-fractures and there are obvious differences between wells in the development characteristics of micro-fractures;the organic pores adjacent to the micro-fractures are poorly developed,while the inorganic pores are well preserved.(2)According to the type,development degree and contact relationship of organic pore and micro-fracture,the pore-fracture configuration of the shale reservoir is divided into four types.(3)Based on the differences in NMR T_(2) spectra of shale samples saturated with oil and water,an evaluation parameter of pore-fracture configuration was constructed and calculated.The smaller the parameter,the better the pore-fracture configuration is.(4)The shale reservoir with good pore-fracture configuration has well-developed organic pores,high porosity,high permeability and high gas content,while the shale reservoir with poor pore-fracture configuration has micro-fractures developed,which improves the natural gas conductivity and leads to low porosity and gas content of the reservoir.(5)Based on pore-fracture configuration,from the perspective of organic matter generating hydrocarbon,micro-fracture providing migration channel,three types of micro gas-filled models of shale gas were established.

Acoustic emission-based numerical simulation of tectonic stress field for tectoclase prediction in shale reservoirs of the northern Guizhou area, China

Natural fractures,like tectoclases,are essential in the formation of shale gas reservoirs and have been the focus of study for shale gas development.Tectoclases provide most storage space for gas and are largely controlled by the paleo-tectonic stress field in shale reservoirs of the Niutitang Formation,northern Guizhou area,China.An accurate prediction of the development and distribution of tectoclases in the reservoirs is of great significance to exploring and developing shale gas sweet spots in the area.Based on geological structure evolution and fracture characterization,this study is focused on factors that control the fracture development in the Niutitang Formation shale reservoirs in northern Guizhou through characterization and modeling of geomechanisms and tectonic movements.A geomechanical model is formulated for the shale reservoirs against the geological background of the area.On this basis,the fractures are predicted by using the acoustic emission data.Numerical simulation results show that the development and distribution of tectoclase is controlled by fault zones,some of which have no obvious turning points with tectoclase in the middle sections being more developed and fragmented than those at the two ends.Some of these have obvious S-shaped turning points where tectoclases are the most developed and fragmented.

Quantitative characterization of the brittleness of deep shales by integrating mineral content,elastic parameters,in situ stress conditions and logging analysis

Deep shale reservoirs(3500–4500 m)exhibit significantly different stress states than moderately deep shale reservoirs(2000–3500 m).As a result,the brittleness response mechanisms of deep shales are also different.It is urgent to investigate methods to evaluate the brittleness of deep shales to meet the increasingly urgent needs of deep shale gas development.In this paper,the quotient of Young’s modulus divided by Poisson’s ratio based on triaxial compression tests under in situ stress conditions is taken as SSBV(Static Standard Brittleness Value).A new and pragmatic technique is developed to determine the static brittleness index that considers elastic parameters,the mineral content,and the in situ stress conditions(BIEMS).The coefficient of determination between BIEMS and SSBV reaches 0.555 for experimental data and 0.805 for field data.This coefficient is higher than that of other brittleness indices when compared to SSBV.BIEMS can offer detailed insights into shale brittleness under various conditions,including different mineral compositions,depths,and stress states.This technique can provide a solid data-based foundation for the selection of‘sweet spots’for single-well engineering and the comparison of the brittleness of shale gas production layers in different areas.

A method for predicting the probability of formation of complex hydraulic fracture networks in shale reservoirs: development and application

Shales can form a complex fracture network during hydraulic fracturing, which greatly increases the stimulated reservoir volume (SRV) and thus significantly increases oil or gas production. It is therefore important to accurately predict the probability of formation of the hydraulic fracture network for shale gas exploration and exploitation. Conventional discriminant criteria are presented as the relationship curves of stress difference vs. intersection angle. However, these methods are inadequate for application in the field. In this study, an effective and quantitative prediction method relating to the probability of complex fracture network formation is proposed. First, a discriminant criterion of fracture network was derived. Secondly, Monte Carlo simulation was applied to calculate the probability of the formation of the complex fracture network. Then, the method was validated by applying it to individual wells of two active shale gas blocks in the Sichuan Basin, China. Results show that the probabilities of fracture network are 0.98 for well JY1 and 0.26 for well W204, which is consistent with the micro-seismic hydraulic fracturing monitoring and actual gas production. Finally, the method was further extended to apply for the regional scale of the Sichuan Basin, where the general probabilities of fracture network formation are 0.32–1 and 0.74–1 for Weiyuan and Jiaoshiba blocks, respectively. The Jiaoshiba block has, therefore, an overall higher probability for formation of fracture network than the Weiyuan block. The proposed method has the potential in further application to evaluation and prediction of hydraulic fracturing operations in shale reservoirs.

Exploring pore-scale production characteristics of oil shale after CO_(2) huff‘n’puff in fractured shale with varied permeability

Recent studies have indicated that the injection of carbon dioxide(CO_(2))can lead to increased oil recovery in fractured shale reservoirs following natural depletion.Despite advancements in understanding mass exchange processes in subsurface formations,there remains a knowledge gap concerning the disparities in these processes between the matrix and fractures at the pore scale in formations with varying permeability.This study aims to experimentally investigate the CO_(2) diffusion behaviors and in situ oil recovery through a CO_(2) huff‘n’puff process in the Jimsar shale oil reservoir.To achieve this,we designed three matrix-fracture models with different permeabilities(0.074 mD,0.170 mD,and 0.466 mD)and experimented at 30 MPa and 91°C.The oil concentration in both the matrix and fracture was monitored using a low-field nuclear magnetic resonance(LF-NMR)technique to quantify in situ oil recovery and elucidate mass-exchange behaviors.The results showed that after three cycles of CO_(2) huff‘n’puff,the total recovery degree increased from 30.28%to 34.95%as the matrix permeability of the core samples increased from 0.074 to 0.466 mD,indicating a positive correlation between CO_(2) extraction efficiency and matrix permeability.Under similar fracture conditions,the increase in matrix permeability further promoted CO_(2) extraction efficiency during CO_(2) huff‘n’puff.Specifically,the increase in matrix permeability of the core had the greatest effect on the extraction of the first-cycle injection in large pores,which increased from 16.42%to 36.64%.The findings from our research provide valuable insights into the CO_(2) huff‘n’puff effects in different pore sizes following fracturing under varying permeability conditions,shedding light on the mechanisms of CO_(2)-enhanced oil recovery in fractured shale oil reservoirs.

Implication of Water-Rock Interaction for Enhancing Shale Gas Production

Horizontal well drilling and multi-stage hydraulic fracturing technologies are at the root of commercial shale gas development and exploitation.During these processes,typically,a large amount of working fluid enters the formation,resulting in widespread water-rock interaction.Deeply understanding such effects is required to optimize the production system.In this study,the mechanisms of water-rock interaction and the associated responses of shale fabric are systematically reviewed for working fluids such as neutral fluids,acid fluids,alkali fluids and oxidative fluids.It is shown that shale is generally rich in water-sensitive components such as clay minerals,acidsensitive components(like carbonate minerals),alkali-sensitive components(like quartz),oxidative-sensitive components(like organic matter and pyrite),which easily lead to change of rock fabric and mechanical properties owing to water-rock interaction.According to the results,oxidizing acid fluids and oxidizing fracturing fluids should be used to enhance shale gas recovery.This study also indicates that an aspect playing an important role in increasing cumulative gas production is the optimization of the maximum shut-in time based on the change point of the wellhead pressure drop rate.Another important influential factor to be considered is the control of the wellhead pressure considering the stress sensitivity and creep characteristics of the fracture network.

Shale Fracturability Graphic Template Based onMixed Analytic Hierar-chy Process andMutation Theory

Due to the depletion of conventional energy reserves,there has been a global shift towards non-conventional energy sources.Shale oil and gas have emerged as key alternatives.These resources have dense and heterogeneous reservoirs,which require hydraulic fracturing to extract.This process depends on identifying optimal fracturing layers,also known as‘sweet spots’.However,there is currently no uniform standard for locating these sweet spots.This paper presents a new model for evaluating fracturability that aims to address the current gap in the field.The model utilizes a hierarchical analysis approach and a mutation model,and is distinct in its use of original logging data to generate a fracturability evaluation map.Using this paper’s shale fracturing sweet spot evaluation method based on a two-step mutation model,four wells in different blocks of Fuling and Nanchuan Districts in China were validated,and the results showed that the proportion of high-yielding wells on the sweet spot line could reach 97.6%,while the proportion of low-producing wells was only 78.67%.Meanwhile,the evaluation results of the model were compared with the microseismic data,and the matching results were consistent.

Mutual impact of true triaxial stress, borehole orientation and bedding inclination on laboratory hydraulic fracturing of Lushan shale

Unconventional resources like shale gas has been the focus of intense research and development for two decades. Apart from intrinsic geologic factors that control the gas shale productivity (e.g. organic matter content, bedding planes, natural fractures, porosity and stress regime among others), external factors like wellbore orientation and stimulation design play a role. In this study, we present a series of true triaxial hydraulic fracturing experiments conducted on Lushan shale to investigate the interplay of internal factors (bedding, natural fractures and in situ stress) and external factors (wellbore orientation) on the growth process of fracture networks in cubic specimens of 200 mm in length. We observe relatively low breakdown pressure and fracture propagation pressure as the wellbore orientation and/or the maximum in situ stress is subparallel to the shale bedding plane. The wellbore orientation has a more prominent effect on the breakdown pressure, but its effect is tapered with increasing angle of bedding inclination. The shale breakdown is followed by an abrupt response in sample displacement, which reflects the stimulated fracture volume. Based on fluid tracer analysis, the morphology of hydraulic fractures (HF) is divided into four categories. Among the categories, activation of bedding planes (bedding failure, BF) and natural fractures (NF) significantly increase bifurcation and fractured areas. Under the same stress regime, a horizontal wellbore is more favorable to enhance the complexity of hydraulic fracture networks. This is attributed to the relatively large surface area in contact with the bedding plane for the horizontal borehole compared to the case with a vertical wellbore. These findings provide important references for hydraulic fracturing design in shale reservoirs.

Lacustrine shale oiliness influenced by diabase intrusions in the Paleogene Funing Formation,Subei Basin,China

The research on the correlation between hydrocarbon accumulations and magmatic activities has always attracted aroused much wide attention.Existing research has primarily the hydrocarbon generations capability of source rocks and the quality of reservoirs by diabase intrusions.whereas,rare systematic research has been conducted on the oiliness and enrichment mechanism.To be specific,the diabase intrusive zone,the contact metamorphic zone and the normal shale zone of the Funing Formation in the Gaoyou Sag,Subei Basin were taken as the object of this study.Moreover,in this study,the hydrocarbon generation quality,reservoir quality,and oil-bearing quality of diabase-metamorphic zone-normal shale were evaluated using X-ray diffractions,argon ion polishing-field emission scanning electron microscope,energy spectrum,rock slice/light-sheet microscopic observations,organic geochemical tests,N_(2) gas adsorption and 2D NMR tests.The results indicated that the intrusive zone,the metamorphic zone,and the normal zone were formed in order by the degree of effect of diabase intrusions.Secondly,the oil content of different parts exhibited significant heterogeneity due to the baking effect of diabase,and the metamorphic zone had the significantly better oil-bearing nature than the intrusive zone.Lastly,a distribution model was proposed for the diabase intrusive zone-metamorphic zone-normal surrounding rock zone.

A New Discovery on the Deformation Behavior of Shale Gas Reservoirs Affecting Pore Morphology in the Juhugeng Coal Mining Area of Qinghai Province, Northwest China

Objective The Juhugeng mining area in Qinghai Province of northwest China has attracted wide attention among geologists for it hosts typical coal measure gases.The shale gas reservoirs were reformed by intensive structural movements during geological periods,

Influence of Bedding and Mineral Composition on Mechanical Properties and Its Implication for Hydraulic Fracturing of Shale Oil Reservoirs

The premise of hydraulic fracturing is to have an accurate and detailed understanding of the rock mechanical properties and fracture propagation law of shale reservoirs. In this paper,a comprehensive evaluation of the mechanical properties of the shale oil reservoir in the south of Songliao Basin is carried out. Based on the experiments and the in-situ stress analysis, the fracture propagation law of three types of shale reservoirs is obtained,and the suggestions for fracturing are put forward. The results have shown that the fracture propagation of pure shale and low mature reservoir is easy to open along the bedding plane under compression loading,which is greatly influenced by the bedding. Sand-bearing shale is slightly better,the fractures of which are not easy to open along the bedding plane. The mechanical experimental results show that all the samples have the characteristics of low compressive strength,low Young’s modulus and strong anisotropy,indicating that the shale oil reservoir is certain plastic,which is related to its high clay mineral content and controlled by the bedding development. Compared with pure shale and low mature shale,the sandbearing shale has less clay content and less developed bedding,which maybe the main reason for its slightly better brittleness. Overall,the expansion of hydraulic fracture is controlled by in-situ stress and bedding. Because of the development of bedding,it is easy to form horizontal fractures. Thus it is not suitable for horizontal well fracturing.Because of the high content of clay minerals,the applicability of conventional slick hydraulic fracturing fluid is poor. It is suggested to use vertical well or directional well to carry out volume fracturing. In this way,the effect of bedding can be effectively used to open and connect the bedding and form a larger fracture network.

Geological characteristics and high production control factors of shale gas reservoirs in Silurian Longmaxi Formation, southern Sichuan Basin, SW China

Marine shale gas resources have great potential in the south of the Sichuan Basin in China.At present,the high-quality shale gas resources at depth of 2000–3500 m are under effective development,and strategic breakthroughs have been made in deeper shale gas resources at depth of 3500–4500 m.To promote the effective production of shale gas in this area,this study examines key factors controlling high shale gas production and presents the next exploration direction in the southern Sichuan Basin based on summarizing the geological understandings from the Lower Silurian Longmaxi Formation shale gas exploration combined with the latest results of geological evaluation.The results show that:(1)The relative sea depth in marine shelf sedimentary environment controls the development and distribution of reservoirs.In the relatively deep water area in deep-water shelf,grade-I reservoirs with a larger continuous thickness develop.The relative depth of sea in marine shelf sedimentary environment can be determined by redox conditions.The research shows that the uranium to thorium mass ratio greater than 1.25 indicates relatively deep water in anoxic reduction environment,and the uranium to thorium mass ratio of 0.75–1.25 indicates semi-deep water in weak reduction and weak oxidation environment,and the uranium to thorium mass ratio less than 0.75 indicates relatively shallow water in strong oxidation environment.(2)The propped fractures in shale reservoirs subject to fracturing treatment are generally 10–12 m high,if grade-I reservoirs are more than 10 m in continuous thickness,then all the propped section would be high-quality reserves;in this case,the longer the continuous thickness of penetrated grade-I reservoirs,the higher the production will be.(3)The shale gas reservoirs at 3500–4500 m depth in southern Sichuan are characterized by high formation pressure,high pressure coefficient,well preserved pores,good pore structure and high proportion of free gas,making them the most favorable new field for shale gas exploration;and the pressure coefficient greater than 1.2 is a necessary condition for shale gas wells to obtain high production.(4)High production wells in the deep shale gas reservoirs are those in areas where Long11-Long13 sub-beds are more than 10 m thick,with 1500 m long horizontal section,grade-I reservoirs penetration rate of over 90%,and fractured by dense cutting+high intensity sand injection+large displacement+large liquid volume.(5)The relatively deep-water area in the deep-water shelf and the area at depth of 3500–4500 m well overlap in the southern Sichuan,and the overlapping area is the most favorable shale gas exploration and development zones in the southern Sichuan in the future.With advancement in theory and technology,annual shale gas production in the southern Sichuan is expected to reach 450×108 m3.

Will the future of shale reservoirs lie in CO2 geological sequestration?

CO2 geological sequestration in a depleted shale gas reservoir is a promising method to address the global energy crisis as well as to reduce greenhouse gas emissions. Though improvements have been achieved by many researchers, the carbon sequestration and enhanced gas recovery(CS-EGR) in shale formations is still in a preliminary stage. The current research status of CO2 sequestration in shale gas reservoirs with potential EGR is systematically and critically addressed in the paper. In addition, some original findings are also presented in this paper. This paper will shed light on the technology development that addresses the dual problem of energy crisis and environmental degradation.

Quantitative characterization of shale pore connectivity and controlling factors using spontaneous imbibition combined with nuclear magnetic resonance T_(2)and T_(1)-T_(2)

Shale oil can be extracted from shale by using interconnected pore networks.The migration of hydrocarbon molecules within the shale is controlled by pore connectivity.However,assessing the pore connectivity of shale oil reservoirs is uncommon.To characterize pore connectivity and clarify its controlling factors,this study used spontaneous imbibition(SI)combined with nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies on shale oil reservoirs selected from the Shahejie Formation in the Dongying Sag,Bohai Bay Basin.According to the findings,the SI processes of shales include fast-rising,slow-rising,and stable stages.The fast-rising stage denotes pore connectivity.The shales studied have poor connectivity,with lower imbibition slopes and connected porosity ratios,but large effective tortuosity.During the SI process,micropores have the highest imbibition saturation,followed by mesopores and macropores.Furthermore,n-dodecane ingested into micropores appears primarily as adsorbed,whereas n-dodecane appears primarily as free states in mesopores and macropores during the SI process.The pore connectivity of the shales under study is primarily controlled by inorganic minerals.Quartz and feldspar develop large and regular pores,resulting in better pore connectivity,whereas clay minerals and calcite with plenty of complex intragranular pores do not.Organic matter negatively influences pore connectivity because the dissolution of calcite by organic acid produced during hydrocarbon generation leads to a more complex and heterogeneous pore structure.This study sheds light on the pore connectivity and controlling factors of the shale oil reservoir and aids in the understanding of shale oil mobility.