At present,shale gas exploration and development in China is faced with some problems,such as the imperfect evaluation system of reservoir effectiveness and the limitations of reservoir evaluation system on efficient d...At present,shale gas exploration and development in China is faced with some problems,such as the imperfect evaluation system of reservoir effectiveness and the limitations of reservoir evaluation system on efficient development of shale gas.In order to improve the content and the standard of reservoir evaluation,this paper analyzed the shortcomings and challenges in the static evaluation of shale gas reservoirs on the basis of existing reservoir evaluation,and established a method for evaluating shale gas reservoir effectiveness and a scheme for classifying pore systems.Then,the dynamic evaluation parameters after shale fracturing and their effects on drainage and production measures were discussed.In addition,the potential evaluation parameters of“automatic mitigating water blocking”were studied,and a comprehensive reservoir evaluation system of“staticedynamic”combination was established.And the following research results were obtained.First,new challenges to the shale gas reservoir evaluation are emerged as the lack of in-depth study on“reservoir effectiveness,dynamic evaluation parameter system after fracturing and drainage and production measures after fracturing”,which leads to the serious lag of existing shale gas reservoir evaluation system behind production.Second,the evaluation of reservoir effectiveness is mainly presented as the evaluation on the lower limit of effective porosity,and is embodied in the influence of clay bound water and unconnected pores on the development of shale gas.Third,the development of shale gas reservoir evaluation follows the trend of refining the static reservoir evaluation parameters,defining the potential evaluation indexes of“automatic mitigating water blocking”and establishing the reservoir comprehensive evaluation system of“staticedynamic”combination.Fourth,a post-frac dynamic evaluation system is determined for the potential evaluation indexes of“automatic mitigating water blocking”(e.g.,wettability,water imbibition retention capacity,water imbibition expansion mode,expansion rate,and water imbibition cracking capacity).Fifth,a reservoir evaluation idea is put forward that“static evaluation of shale gas reservoir is the foundation and postfrac dynamic evaluation is the complement”,and a comprehensive reservoir evaluation system is established of“staticedy-namic”combination suitable for the evaluation of marine shale gas reservoirs in China.展开更多
The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas re...The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas reservoirs,do not take the unconnected pores into account,which impacts the evaluation accuracy of reservoir pore effectiveness.To solve this problem,this paper took the shale of Lower Silurian Longmaxi Formation in the southern Sichuan Basin as the research object to carry out experiments on core porosity,centrifugal+gradual drying NMR after saturated with brine and NMR freezeethaw using plunger samples and crushed samples to analyze the volume,main development location and main pore size distribution range of unconnected pores.Then,the pore systems were classified,and the lower limit of effective pore size of connected gas-bearing pores was determined.Finally,the total pore effectiveness of shale gas reservoirs was evaluated,and the influence of unconnected pores on the development of shale gas was discussed.And the following research results were obtained.First,there are a large number of unconnected pores in the shale gas reservoirs of the study area,accounting for 30.23%.Most of them are mainly developed in organic matters and a few are developed in clay minerals.The distribution of pore size ranges from 5 nm to 30 nm.Second,T_(2)cut-off value of clay bound water in the shale gas reservoirs of the study area is 0.26 ms,whose corresponding pore size is 5.35 nm,which is the lower limit of the effective pore size.Third,large-scale hydraulic fracturing can improve the unconnected pores with the size more than 5.35 nm,so effective development of shale gas will be realized.Fourth,after hydraulic fracturing stimulation,the unconnected pores can increase the storage space of fracturing fluid in the matrix,absorb the fracturing fluid in the fractures,replace the shale gas in the pores and promote the automatic alleviation of water lock in shale gas reservoirs,so the single-well shale gas production will be increased.In conclusion,fluid occurrence and pore system in shale pores can be quantitatively divided by means of centrifugal+gradual temperature drying method combined with NMR experiments,mobile water and capillary bound water can be determined by the high speed centrifugal+NMR experiments,and capillary bound water and clay bound water can be determined by the gradual drying t NMR experiments.展开更多
Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margi...Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margin zone(MZ)to the slip central zone(CZ)of the fault gouge in the Beichuan-Yingxiu surface rupture zone of the Wenchuan Earthquake.Results show that the clay minerals contents increase from the MZ to CZ,and the quartz and plagioclase contents slight decrease.An increasing enrichment in Al_(2)O_(3),Fe_(2)O_(3),and K_(2)O are observed toward the CZ;the decomposition of quartz and plagioclase,as well as the depletion of Si O_(2),Ca O,Na_2O,and P_(2)O_(5)suggest that the alkaline-earth elements are carried away by the fluids.It can be explained that the stronger coseismic actions in the CZ allow more clay minerals to form,decompose quartz and plagioclase,and alter plagioclase to chlorite.The mass loss in the CZ is larger than that in MZ,which is maybe due to the more concentrated stress in the strongly deformed CZ,however other causes will not be excluded.展开更多
Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettabilit...Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettability by dielectric spectra which contained abundant information.To study the rock wettability from dielectric dispersion,four rock samples with different wettabilities were used to design an experimental measurement flow.The relative dielectric permittivity in the frequency range of 100 Hz-10MHz and nuclear magnetic resonance T_(2)spectra of the samples were obtained.Subsequently,the wettabilities of the rocks were verified by the T_(2)spectra.The dielectric dispersions of the samples under different conditions were analyzed.Furthermore,the simulated-annealing(SA)algorithm was used to invert the wettability and related parameters of the rocks by a dielectric dispersion model.The results indicated that the dielectric permittivity of lipophilic rocks is lower than that of hydrophilic rocks,and that the dielectric permittivity of hydrophilic rocks decreases faster as the frequency increases.The dielectric permittivity in the high-frequency band is associated with the water content.The rock wettability parameters obtained via inversion agreed well with the T_(2)spectra,and the saturation index of the rocks.The errors between the rock permittivity calculated by the inverted parameters and the experimentally measured values were minor,indicating that rock wettability could be accurately characterized using dielectric dispersion data.展开更多
Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model...Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model is proposed to characterize the effect of pressure drop rate on fracture permeability.Furthermore,a production prediction model is introduced accounting for a non-uniform hydraulic fracture conductivity distribution.The results reveal that increasing the fracture conductivity leads to a rapid daily production increase in the early stages.However,above 0.50 D·cm,a further increase in the fracture conductivity has a limited effect on shale gas production growth.The initial production is lower under pressure-controlled conditions than that under pressure-release.For extended pressure control durations,the cumulative production initially increases and then decreases.For a fracture conductivity of 0.10 D·cm,the increase in production output under controlled-pressure conditions is~35%.For representative deep shale gas wells(Southern Sichuan,China),if the pressure drop rate under controlled-pressure conditions is reduced from 0.19 to 0.04 MPa/d,the EUR increase for 5 years of pressure-controlled production is 41.0 million,with an increase percentage of~29%.展开更多
To formulate fluids with flowback water,produced water directly to improve the utilization rate of recycling and reduce the adsorption damage of slick water to reservoirs,a high salt tolerance and low adsorption drag ...To formulate fluids with flowback water,produced water directly to improve the utilization rate of recycling and reduce the adsorption damage of slick water to reservoirs,a high salt tolerance and low adsorption drag reducer was designed and prepared by introducing polar cation fragments to enhance the non-covalent interactions between the chains.The drag reducer was characterized by IR and NMR.Friction resistance and viscosity tests were conducted to evaluate its salt resistance property.Static adsorption and dynamic adsorption retention tests were carried out to evaluate the damage of this reducer to shale reservoirs.The introduction of cation units into the molecular structure can weak the shielding effect of metal cations to some extent,so the drag reducer can keep a stable molecular structure and good resistant reducing performance under high salinity.The enhancement of non-covalent interaction between chains decreased the free polarity sites,further reduced the possibility of hydrogen bonding between drag reducer molecules and shale.In high salinity condition,both the adsorption capacity of the drag reducer on the shale surface and the average damage rate to the core permeability are low.Compared with the conventional salt-tolerant system,the overall liquid cost was reduced by 17%and the production per well increased by 44%.The application of this slick water system has achieved remarkable results.展开更多
In China,marine natural gas hydrate(NGH)resources are mainly distributed in the deepwater areas of 300-3000 m deep in the coastal continental shelf,and they are characterized by weak cementation and non-diagenesis.In ...In China,marine natural gas hydrate(NGH)resources are mainly distributed in the deepwater areas of 300-3000 m deep in the coastal continental shelf,and they are characterized by weak cementation and non-diagenesis.In order to test and study this type of NGH,it is necessary to prepare samples quickly in situ in large quantities.At present,the commonly used preparation technologies(e.g.stirring method,spraying method and bubbling method)are defective with slow generation and low gas storage density.In view of this,the 1062 L rapid non-diagenetic NGH preparation kettle was designed and developed independently.Then,based on the physical properties of non-diagenetic NGH in the South China Sea,NGH preparation tests were carried out on stirring method,spraying method,bubbling method and“three-in-one”method(the combination of stirring method,spraying method and bubbling method).Temperature,pressure,resistivity and reaction time in the process of test were tested,and NGH generation situations and preparation efficiency of different preparation processes were analyzed and compared.And the following research results were obtained.First,in the process of NGH preparation by stirring method,spraying method and bubbling method,respectively,the generated NGH increases slowly and spreads the whole liquid level gradually.Second,inducing period is obvious in the preparation process by the stirring method,but not obvious by the spraying method,the bubbling method and the“three-in-one”method.Third,in the process of NGH preparation by stirring method,spraying method,bubbling method and“three-in-one”method,the resistivity increases as the reaction goes,and its change trend is basically accordant with the NGH preparation rate.Fourth,the preparation cycle of NGH by“three-in-one”method is greatly shorter than that by single preparation method.The preparation time by stirring method,spraying method and bubbling method is about 5.14 times,3.59 times and 3.16 times that of“three-in-one”method respectively.In conclusion,the 1062 L rapid NGH preparation kettle developed in this paper can prepare marine non-diagenetic NGH samples quickly in situ.And compared with single preparation method,“three-in-one”method is much higher in NGH preparation efficiency.展开更多
With complex lithology and reservoir types,as well as high concealment and heterogeneity,tight reservoirs in the Sichuan Basin involve significant uncertainties in gas-water relationship.Since NMR logging can effectiv...With complex lithology and reservoir types,as well as high concealment and heterogeneity,tight reservoirs in the Sichuan Basin involve significant uncertainties in gas-water relationship.Since NMR logging can effectively solve problems related to the multiple results of conventional logging operations,it can be deployed for accurate assessment of the properties of formation fluids.Accordingly,different NMR logging activation sets were assessed in accordance with the specific features of tight reservoirs in the basin.With consideration to NMR logging data obtained under different activation sets and testing data of wells,the optimal NMR logging activation set was identified.Moreover,with relaxation characteristics of rocks,gas and water as theoretical foundations,the T_(2) gas and water relaxation characteristics were reviewed to highlight the impacts of porosity,pore sizes,fluid properties and other factors of tight reservoirs on T_(2) horizontal relaxation distribution.According to the research results,D9TWE3 can be seen as the most suitable NMR logging activation set for tight reservoirs in the Sichuan Basin;reservoir tightness is the key influence factor for the distribution of gas/water relaxation in tight clastic reservoirs;generally,in tight sandstone reservoirs,natural gas shows a longer T_(2) relaxation time than water;in fracture-vug type carbonate reservoirs,the right peak of T_(2) distribution spectrum of gas layers is frontal,while the right peak in T_(2) distribution spectrum of water layers is backward.In conclusion,the standards for gas/water relaxation in tight sandstone and carbonate reservoirs in the Sichuan Basin can help effectively determine the physical properties of fluids in tight reservoirs with porosity of 4-10%.Such standards provide reliably technical supports for gas/water identification,reserves estimation and productivity construction in tight reservoirs of the Sichuan Basin.展开更多
Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production...Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production wells is less than half the inter-well spacing(typically 400-500 m).To address this,infill drilling has become a widely adopted and effective strategy for enhancing reservoir contact andmobilizing previously untapped reserves.However,this approach has introduced significant inter-well interference,complicating production dynamics and performance evaluation.The two primary challenges hindering efficient deployment of infill wells are:(1)the quantitative assessment of hydraulic and pressure connectivity between infill wells and their associated parent wells,and(2)the accurate estimation of platform-scale Estimated Ultimate Recovery(EUR)following infill implementation.This study presents a novel framework to quantify inter-well connectivity by deriving a material balance equation tailored for shale gas infill well groups,explicitly incorporating gas adsorption and desorption mechanisms.The model simultaneously evaluates formation pressure evolution and crossflow behavior between wells,offering a robust analytical basis for performance prediction.For infill wells intersecting the drainage boundaries of parent wells,EUR is estimated using an analytical model developed for multi-stage hydraulically fractured horizontal wells.Meanwhile,the EUR of the parent wells is obtained by summing their pre-infill EUR with the final inter-well crossflow contribution.展开更多
Sedimentary facies is an important factor influencing shale gas accumulation. It not only controlls hydrocarbon generation, but also affects reservoir characteristics and distribution. This paper discusses the Lower S...Sedimentary facies is an important factor influencing shale gas accumulation. It not only controlls hydrocarbon generation, but also affects reservoir characteristics and distribution. This paper discusses the Lower Silurian Longmaxi Formation in the south of the Sichuan Basin. Outcrop, core, drilling and logging data identify the sedimentary facies of the formation as continental shelf facies, which is divided into two subfacies： an inner shelf and an outer shelf subfacies. These two subfacies can be further divided into seven microfacies： muddy silty shallow shelf, calcareous silty shallow shelf, muddy limy shallow shelf, storm flow, muddy deep shelf, silty muddy deep shelf and contour current microfacies. Vertical and horizontal distribution of microfacies establishes a sedimentation model of the continental shelf facies. Combined with analization or calculation of geochemical, mineralogical, physical and gas-bearing properties of samples, sedimentary microfacies is evaluated using nine parameters： total organic carbon content, effective shale continuous thickness, vitrinite reflectance, kerogen type, mineral components, porosity, permeability, water saturation and gas content. The evaluation revealed that the most favorable facies for shale gas exploration and development are the muddy deep shelf and part of the silty muddy deep shelf microfacies, with TOC more than 2%, siliceous component over 50%, clay less than 30%, porosity more than 3%, water saturation lower than 40%, gas content greater than 2 m3/t. These results provide a theoretical basis for deciston-making on the most promising areas for shale gas exploration in the Sichuan Basin and for marine shale gas exploration and development in South China.展开更多
Diamond,moissanite and a variety of other minerals,similar to those reported from ophiolites in Xizang and northern Russia,have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian O...Diamond,moissanite and a variety of other minerals,similar to those reported from ophiolites in Xizang and northern Russia,have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian Orogenic Belt,north China.The chromitites are small,podiform and vein-like bodies hosted in dunite,clinopyroxene-bearing peridotite,troctolite and gabbro.All of the analysed chromite grains are relatively Al-rich,with Cr^#[100Cr/(Cr+Al)]of about 47-53.Preliminary studies of mainly disseminated chromitite from ore body No.3756 have identified more than 30 mineral species in addition to diamond and moissanite.These include oxides(mostly hematite,magnetite,ruffle,anatase,cassiterite,and quartz),sulfides(pyrite,marcasite and others),silicates(magnesian olivine,enstatite,augite,diopside,uvarovite,pyrope,orthoclase,zircon,sphene,vesuvianite,chlorite and serpentine)and others(e.g.,calcite,monazite,glauberite,iowaite and a range of metallic alloys).This study demonstrates that diamond,moissanite and other exotic minerals can occur in high-Al,as well as high-Cr chromites,and significantly extends the geographic and age range of known diamond-bearing ophiolites.展开更多
Porous carbonate reservoirs,prevalent in the Middle East,are lithologically dominated by bioclastic limestones,exhibiting high porosity,low permeability,intricate pore structure,and strong heterogeneity.Waterflooding ...Porous carbonate reservoirs,prevalent in the Middle East,are lithologically dominated by bioclastic limestones,exhibiting high porosity,low permeability,intricate pore structure,and strong heterogeneity.Waterflooding through horizontal wells is commonly used for exploiting these reservoirs.However,challenges persist,such as significant uncertainty and complex operational procedures regarding adjustment effects during the exploitation.The USH reservoir of the Cretaceous D oilfield,Oman exemplifies typical porous carbonate reservoirs.It initially underwent depletion drive using vertical wells,followed by horizontal well waterflooding in the late stage.Currently,the oilfield is confronted with substantial developmental challenges,involving the understanding of residual oil distribution,effective water cut control,and sustaining oil production since it has entered the late development stage.Employing a microscopic visualization displacement system equipped with electrodes,this study elucidated the waterflooding mechanisms and residual oil distribution in the late-stage development of the USH reservoir.The results reveal that the reservoir's vertical stacking patterns act as the main factor affecting the horizontal well waterflooding efficacy.Distinct water flow channels emerge under varying reservoir stacking patterns,with post-waterflooding residual oil predominantly distributed at the reservoir's top and bottom.The oil recovery can be enhanced by adjusting the waterflooding's flow line and intensity.The findings of this study will provide theoretical insights of waterflooding mechanisms and injection-production adjustments for exploiting other porous carbonate reservoirs in the Middle East through horizontal wells.展开更多
Romashkino oil field has large oilfield area, small formation dip, many reservoir layers, wide oil-water transition zone and complicated sedimentary environment. Since development, 3 overall development plannings and ...Romashkino oil field has large oilfield area, small formation dip, many reservoir layers, wide oil-water transition zone and complicated sedimentary environment. Since development, 3 overall development plannings and adjustments of individual block have been established. This achieves a high oil production. However, the recoverable reserves of major oil layer with high production become smaller and smaller and the water cut increases over time, the production ability of oil layer decreases. The development status of oil layer of mining siltstone, oil-water transition zone and oil layer with upswept injected water cannot be changed under present dilute well network condition, because there is no reinforced measurement to water well. This results the low oil production of Romashkino oil field. In order to improve oil production rate and reach the designed oil recovery, Romashkino oil field has been implemented many added cuttings since development. Resent researches about Romashkino oil field show: in later oilfield development stage, sidetrack and lateral drilling horizontal wells technology is very reasonable;formation hydraulic fracturing technology has been widely used in recent years;in tertiary oil recovery, sweep efficiency and flooding efficiency related technologies have been taken. This offers reference and guidance for the effective and reasonable oil field development in later period.展开更多
Diamonds, moissanite and a variety of other minerals, similar to those reported from ophiolites in Tibet and northern Russia （Yang et al., 2011）, have recently been discovered in chromitites of the Hegenshan ophioli...Diamonds, moissanite and a variety of other minerals, similar to those reported from ophiolites in Tibet and northern Russia （Yang et al., 2011）, have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian Orogenic Belt. The Hegenshan ophiolite is located in Xilinhaote, Inner Mongolia,展开更多
Previously reported in the Mesozonic Tibet and the early Paleozoic Polar Ural,Russia , diamond and other deep minerals are found in ophiolite mantle peridotite chromite that need to be reconsidered ophiolite and chrom...Previously reported in the Mesozonic Tibet and the early Paleozoic Polar Ural,Russia , diamond and other deep minerals are found in ophiolite mantle peridotite chromite that need to be reconsidered ophiolite and chromite traditional understanding of the causes of shallow. The ophiolitic chromitite can be divided two classes, the high-Cr chromitite and high-Al chromitite.展开更多
Reservoir pore spaces(incl.pores,fractures and vugs)are too complex to be predicted by use of the traditional interrelationships between the four properties of reservoirs,thus more and more contradictions occur in res...Reservoir pore spaces(incl.pores,fractures and vugs)are too complex to be predicted by use of the traditional interrelationships between the four properties of reservoirs,thus more and more contradictions occur in reservoir evaluation.A great number of case studies were made to reveal the causes of these contradictions and the corresponding solutions were also proposed.For the reservoirs with complex pore spaces,we found four common types of contradictions between porosity and permeability,porosity and water saturation,absolute permeability and effective permeability,and electrical property and hydrocarbon property.These contradictions are mainly caused by variation of pore types,pore-throat sizes and fracture occurrence.On this basis,the concept of geometrical property was presented and methods were discussed for qualitatively or quantitatively describing the geometrical properties of pores,fractures and vugs.The following findings were achieved.(1)For pores,two relationships were established between pores&throat sizes and rock textures,physical property&fluid property,and between pore types and fluid property&logging responses.(2)For fractures,five relationships were established between occurrence and pore texture index(m),radial extension and deep/shallow borehole resistivity,openness and fracture permeability,occurrence and matrix water saturation,and between development index and lithology.(3)For vugs,two relationships were established between size&connectivity and m value&three porosities derived from logging responses(neutron,density and sonic wave),and filling degree and logging responses.The interrelationships between geometrical property,lithology,physical property,fluid property and electrical property can significantly improve the evaluation of complex reservoirs such as carbonates.展开更多
Increasing the resolution of seismic data has long been a major topic in seismic exploration.Due to the effect of high-frequency noises,traditional methods could only improve the resolution limitedly.To end this,this ...Increasing the resolution of seismic data has long been a major topic in seismic exploration.Due to the effect of high-frequency noises,traditional methods could only improve the resolution limitedly.To end this,this paper newly proposed a high-resolution seismic data processing method based on welleseismic combination after summarizing the research status on high resolution.Synthetic record and seismogram are similar in effective signals but dissimilar in noises.Their effective signals are regular and noises are irregular.And they are similar in adjacent frequency.Based on these“three-regularity”characteristics,the relationship between synthetic record and seismogram was established using the neural network algorithm.Then,the corresponding extrapolation algorithm was proposed based on the self-adaptive geological and geophysical variation of multi-layer network structure.And a model was established by virtue of this method and the theoretical simulation was carried out.In addition,it was tested from the aspects of frequency component and amplitude energy recovery,phase correction,regularity elimination and stochastic noise.And the following research results were obtained.First,this new method can extract high-frequency information as much as possible and remain middle and low-frequency effective information while eliminating the noises.Second,in this method,the idea of traditional methods to denoisefirst and then expand frequency is changed completely and the limitation of traditional methods is broken.It establishes the idea of expanding frequency and denoising simultaneously and increases the resolution to the uttermost.Third,this new method has been applied to a variety of reservoir descriptions and the high-resolution processing results have been improved significantly in precision and accuracy.展开更多
With the popularization and application of fast drilling technology in Sichuan-Chongqing gas provinces,the returned cuttings are fine and even powdered,so the traditional cutting lithology identification methods are n...With the popularization and application of fast drilling technology in Sichuan-Chongqing gas provinces,the returned cuttings are fine and even powdered,so the traditional cutting lithology identification methods are not applicable any longer.In this paper,qualitative lithology identification and quantitative interpretation based on element logging were conducted on the key oil and gas bearing layers in this area according to the principle of elemental geochemistry.The study results show that:(1)different lithologies can be identified easily because of their different element logging characteristics.For example,basalts have the element characteristics of 0.35<Fe/Si<0.55 and Ca/(Na+K)<4.00,while sedimentary rocks have Fe/Si<0.35 or>0.55.(2)Clastic rocks,carbonate rocks,sulphate and transition rocks in the category of sedimentary rocks can be identified based on the element combination of(Al+Si+Fe)and(Ca+Mg+S).Among them,clastic rocks have(Al+Si+Fe)>31%,carbonate rocks have(Al+Si+Fe)<8%and(Ca+Mg+S)<36%,and sulphate rocks have(Al+Si+Fe)<5%and(Ca+Mg+S)>36%.(3)Then,based on the element combination of(Si+K+Ca)tSi/Al and(Al+Si+Fe+K)t(Ca+S)/Mg,sandstone,mudstone(shale),gypsum,dolomite,limestone and transition rocks can be identified.Finally,a qualitative identification chart and a set of quantitative interpretation software of element logging on key horizons in Sichuan-Chongqing gas provinces were developed to make this method convenient for field application.This method was applied on site in ten wells(such as Well MX207)in Sichuan-Chongqing gas provinces.It is indicated that the coincidence rate of lithology identification is in the range of 88.75-95.22%(averaging 92.42%).Obviously,it can satisfy the requirements of fast lithology identification while drilling of key oil and gas horizons in Sichuan-Chongqing gas provinces.展开更多
Hydrocarbon evolution is a crucial part of the global organic carbon cycle,and controls the distribution of hydrocarbon phases within the Earth's crust.However,the pathway and boundary conditions of hydrocarbon ph...Hydrocarbon evolution is a crucial part of the global organic carbon cycle,and controls the distribution of hydrocarbon phases within the Earth's crust.However,the pathway and boundary conditions of hydrocarbon phase evolution remain poorly constrained due to the lack of reliable geological records.Here we present a unique assemblage of sequentially trapped oil,wet gas(C_(1)/∑C_(1-5)=0.74±0.03-0.91±0.01)and dry gas(C_(1)/∑C_(1-5)=0.96±0.01-1)fluid inclusions from the Ediacaran dolomite reservoirs in the central Sichuan Basin,South China,which constrains the pathway and conditions of in situ hydrocarbon phase evolution.Notably,the early trapped oil inclusions(~247 Ma)exhibit abnormally low maturity(0.75%-0.97%vs.2.67%-2.79%VRE for reservoir pyrobitumen).The formation of these oil inclusions is attributed to three key processes:(1)pressure buildup during inclusion oil cracking;(2)leakage of volatile components through decrepitation;and(3)retention of heavy hydrocarbons in the re-equilibrated oil inclusions.In contrast,the reservoir oil underwent in situ cracking and was successively transformed to wet gas(~197 Ma)and dry gas(~116 Ma)with increasing temperature.During this process,a selfregulating mechanism of fluid overpressurization(e.g.,59-86 MPa in 197-182 Ma and 114-151 MPa in 116-109 Ma)and pressure release was identified to facilitate the hydrocarbon-bearing fluid migration.Integration of coexisting aqueous inclusion analyses with burial history reconstruction refines the oil(≤156℃)and wet gas(≤213℃)preservation windows,respectively,in prolonged heating reservoirs.These findings shed new light on hydrocarbon evolution and petroleum exploration in deep strata.展开更多
Most researches of the threshold pressure gradient in tight gas reservoirs are experimental and mainly focus on the transient pressure response, without paying much attention to the transient rate decline. This paper ...Most researches of the threshold pressure gradient in tight gas reservoirs are experimental and mainly focus on the transient pressure response, without paying much attention to the transient rate decline. This paper establishes a dual-porosity rate transient decline model for the horizontal well with consideration of the threshold pressure gradient, which represents the non-Darcy flow in a fracture system. The solution is obtained by employing the Laplace transform and the orthogonal transform. The bi-logarithmic type curves of the dimensionless production rate and derivative are plotted by the Stehfest numerical inversion method. Seven different flow regimes are identified and the effects of the influence factors such as the threshold pressure gradient, the elastic storativity ratio, and the cross flow coefficient are discussed. The presented research could interpret the production behavior more accurately and effectively for tight gas reservoirs.展开更多
基金supported by the National Natural Science Foundation of China"Characterization of the Nanopore Structure and Research on Seepage in Shale Reservoir"(No.:51674044)the Applied Basic Research Project of the Sichuan Province"Research on Intelligent Evaluation System for Key Production Zone of Marine Shale Gas(Provincial Significant Project)"(No.:2019YJ0346)+1 种基金the Significant Emerging Enginecring Project of the Sichuan Province"Research on the method of evaluating the effectiveness of fracturing the shak gas reservoir on the basis of fracturing fluid flow-back law"(No.:2019JDRC0095)the Overseas Expertise Introduction Project for Discipline Innovation(111 project)"Base of Overseas Expertise Introduction for Discipline Innovation of High-Efficiency Development of Deep-Layer Marine Shale Gas"(No.:D18016).
文摘At present,shale gas exploration and development in China is faced with some problems,such as the imperfect evaluation system of reservoir effectiveness and the limitations of reservoir evaluation system on efficient development of shale gas.In order to improve the content and the standard of reservoir evaluation,this paper analyzed the shortcomings and challenges in the static evaluation of shale gas reservoirs on the basis of existing reservoir evaluation,and established a method for evaluating shale gas reservoir effectiveness and a scheme for classifying pore systems.Then,the dynamic evaluation parameters after shale fracturing and their effects on drainage and production measures were discussed.In addition,the potential evaluation parameters of“automatic mitigating water blocking”were studied,and a comprehensive reservoir evaluation system of“staticedynamic”combination was established.And the following research results were obtained.First,new challenges to the shale gas reservoir evaluation are emerged as the lack of in-depth study on“reservoir effectiveness,dynamic evaluation parameter system after fracturing and drainage and production measures after fracturing”,which leads to the serious lag of existing shale gas reservoir evaluation system behind production.Second,the evaluation of reservoir effectiveness is mainly presented as the evaluation on the lower limit of effective porosity,and is embodied in the influence of clay bound water and unconnected pores on the development of shale gas.Third,the development of shale gas reservoir evaluation follows the trend of refining the static reservoir evaluation parameters,defining the potential evaluation indexes of“automatic mitigating water blocking”and establishing the reservoir comprehensive evaluation system of“staticedynamic”combination.Fourth,a post-frac dynamic evaluation system is determined for the potential evaluation indexes of“automatic mitigating water blocking”(e.g.,wettability,water imbibition retention capacity,water imbibition expansion mode,expansion rate,and water imbibition cracking capacity).Fifth,a reservoir evaluation idea is put forward that“static evaluation of shale gas reservoir is the foundation and postfrac dynamic evaluation is the complement”,and a comprehensive reservoir evaluation system is established of“staticedy-namic”combination suitable for the evaluation of marine shale gas reservoirs in China.
基金supported by the National Natural Science Foundation of China“Research on nanopore structure characterization and seepage mechanism of shale reservoirs”(No.:51674044)Chongqing Key Industry Common Key Technology Innovation Special Project“Exploration and development key technology and its application of shale gas in Chongqing”(No.:cstc2017zdcyzdyfx0040)+1 种基金Sichuan Applied Basic Research Project“Research on intelligent evaluation system of marine shale gas construction and production core area(provincial key project)”(No.:2019YJ0340)Sichuan Promising Key Project“Study on evaluation of the fracturing effect of shale gas reservoirs based on the law of fracturing fluid flow back”(No.:2019JDRC0095).
文摘The unconnected gas-bearing pores in shale gas reservoirs may be transformed into“potential recoverable pores”after large scale hydraulic fracturing.However,the mainstream pore classification methods of shale gas reservoirs,do not take the unconnected pores into account,which impacts the evaluation accuracy of reservoir pore effectiveness.To solve this problem,this paper took the shale of Lower Silurian Longmaxi Formation in the southern Sichuan Basin as the research object to carry out experiments on core porosity,centrifugal+gradual drying NMR after saturated with brine and NMR freezeethaw using plunger samples and crushed samples to analyze the volume,main development location and main pore size distribution range of unconnected pores.Then,the pore systems were classified,and the lower limit of effective pore size of connected gas-bearing pores was determined.Finally,the total pore effectiveness of shale gas reservoirs was evaluated,and the influence of unconnected pores on the development of shale gas was discussed.And the following research results were obtained.First,there are a large number of unconnected pores in the shale gas reservoirs of the study area,accounting for 30.23%.Most of them are mainly developed in organic matters and a few are developed in clay minerals.The distribution of pore size ranges from 5 nm to 30 nm.Second,T_(2)cut-off value of clay bound water in the shale gas reservoirs of the study area is 0.26 ms,whose corresponding pore size is 5.35 nm,which is the lower limit of the effective pore size.Third,large-scale hydraulic fracturing can improve the unconnected pores with the size more than 5.35 nm,so effective development of shale gas will be realized.Fourth,after hydraulic fracturing stimulation,the unconnected pores can increase the storage space of fracturing fluid in the matrix,absorb the fracturing fluid in the fractures,replace the shale gas in the pores and promote the automatic alleviation of water lock in shale gas reservoirs,so the single-well shale gas production will be increased.In conclusion,fluid occurrence and pore system in shale pores can be quantitatively divided by means of centrifugal+gradual temperature drying method combined with NMR experiments,mobile water and capillary bound water can be determined by the high speed centrifugal+NMR experiments,and capillary bound water and clay bound water can be determined by the gradual drying t NMR experiments.
基金supported by the research grant from Institute of Crustal Dynamics,China Earthquake Administration(No.ZDJ2019-02)。
文摘Geochemistry of the fault gouge record information on fault behaviors and environmental conditions.We investigated variations in the mineralogical and geochemical compositions of the fault gouge sampled from the margin zone(MZ)to the slip central zone(CZ)of the fault gouge in the Beichuan-Yingxiu surface rupture zone of the Wenchuan Earthquake.Results show that the clay minerals contents increase from the MZ to CZ,and the quartz and plagioclase contents slight decrease.An increasing enrichment in Al_(2)O_(3),Fe_(2)O_(3),and K_(2)O are observed toward the CZ;the decomposition of quartz and plagioclase,as well as the depletion of Si O_(2),Ca O,Na_2O,and P_(2)O_(5)suggest that the alkaline-earth elements are carried away by the fluids.It can be explained that the stronger coseismic actions in the CZ allow more clay minerals to form,decompose quartz and plagioclase,and alter plagioclase to chlorite.The mass loss in the CZ is larger than that in MZ,which is maybe due to the more concentrated stress in the strongly deformed CZ,however other causes will not be excluded.
基金supported by the Beijing Municipal Natural Science Foundation(1242025)。
文摘Wettability has complex effects on the physical properties of reservoir rocks.The wettability of rocks should be characterized accurately to explore and develop oil and gas.Researchers have studied the rock wettability by dielectric spectra which contained abundant information.To study the rock wettability from dielectric dispersion,four rock samples with different wettabilities were used to design an experimental measurement flow.The relative dielectric permittivity in the frequency range of 100 Hz-10MHz and nuclear magnetic resonance T_(2)spectra of the samples were obtained.Subsequently,the wettabilities of the rocks were verified by the T_(2)spectra.The dielectric dispersions of the samples under different conditions were analyzed.Furthermore,the simulated-annealing(SA)algorithm was used to invert the wettability and related parameters of the rocks by a dielectric dispersion model.The results indicated that the dielectric permittivity of lipophilic rocks is lower than that of hydrophilic rocks,and that the dielectric permittivity of hydrophilic rocks decreases faster as the frequency increases.The dielectric permittivity in the high-frequency band is associated with the water content.The rock wettability parameters obtained via inversion agreed well with the T_(2)spectra,and the saturation index of the rocks.The errors between the rock permittivity calculated by the inverted parameters and the experimentally measured values were minor,indicating that rock wettability could be accurately characterized using dielectric dispersion data.
基金supported by the Chongqing Natural Science Foundation Innovation and Development Joint Fund(CSTB2023NSCQ-LZX0078)the Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN202201519),which are gratefully acknowledged.
文摘Pressure control in deep shale gas horizontal wells can reduce the stress sensitivity of hydraulic fractures and improve the estimated ultimate recovery(EUR).In this study,a hydraulic fracture stress sensitivity model is proposed to characterize the effect of pressure drop rate on fracture permeability.Furthermore,a production prediction model is introduced accounting for a non-uniform hydraulic fracture conductivity distribution.The results reveal that increasing the fracture conductivity leads to a rapid daily production increase in the early stages.However,above 0.50 D·cm,a further increase in the fracture conductivity has a limited effect on shale gas production growth.The initial production is lower under pressure-controlled conditions than that under pressure-release.For extended pressure control durations,the cumulative production initially increases and then decreases.For a fracture conductivity of 0.10 D·cm,the increase in production output under controlled-pressure conditions is~35%.For representative deep shale gas wells(Southern Sichuan,China),if the pressure drop rate under controlled-pressure conditions is reduced from 0.19 to 0.04 MPa/d,the EUR increase for 5 years of pressure-controlled production is 41.0 million,with an increase percentage of~29%.
基金Supported by the China National Science and Technology Major Project(2017ZX05023003)National Science Fund for Distinguished Young Scholars(51525404)
文摘To formulate fluids with flowback water,produced water directly to improve the utilization rate of recycling and reduce the adsorption damage of slick water to reservoirs,a high salt tolerance and low adsorption drag reducer was designed and prepared by introducing polar cation fragments to enhance the non-covalent interactions between the chains.The drag reducer was characterized by IR and NMR.Friction resistance and viscosity tests were conducted to evaluate its salt resistance property.Static adsorption and dynamic adsorption retention tests were carried out to evaluate the damage of this reducer to shale reservoirs.The introduction of cation units into the molecular structure can weak the shielding effect of metal cations to some extent,so the drag reducer can keep a stable molecular structure and good resistant reducing performance under high salinity.The enhancement of non-covalent interaction between chains decreased the free polarity sites,further reduced the possibility of hydrogen bonding between drag reducer molecules and shale.In high salinity condition,both the adsorption capacity of the drag reducer on the shale surface and the average damage rate to the core permeability are low.Compared with the conventional salt-tolerant system,the overall liquid cost was reduced by 17%and the production per well increased by 44%.The application of this slick water system has achieved remarkable results.
基金supported by the National Key R&D Program of China“Innovative technologies for test of marine natural gas hydrates through solid fluidization”(No.:2016YFC0304008)National Key R&D Program of China“Technologies and processes for dual-gradient drilling system with riser inflation”(No.:2018YFC0310203)+1 种基金the Medium-and Long-term Development Strategy Research Project of Chinese Academy of Engineering for Engineering Science and Technology“Research on deep-sea natural gas hydrate development strategies,2035”(No.:2017-ZCQ-5)the Fundamental Research for Application Projects of Sichuan Province“Researches on mechanisms and application technologies for the largest and fastest natural gas hydrate preparation in the world”(No.:2019YJ0351).
文摘In China,marine natural gas hydrate(NGH)resources are mainly distributed in the deepwater areas of 300-3000 m deep in the coastal continental shelf,and they are characterized by weak cementation and non-diagenesis.In order to test and study this type of NGH,it is necessary to prepare samples quickly in situ in large quantities.At present,the commonly used preparation technologies(e.g.stirring method,spraying method and bubbling method)are defective with slow generation and low gas storage density.In view of this,the 1062 L rapid non-diagenetic NGH preparation kettle was designed and developed independently.Then,based on the physical properties of non-diagenetic NGH in the South China Sea,NGH preparation tests were carried out on stirring method,spraying method,bubbling method and“three-in-one”method(the combination of stirring method,spraying method and bubbling method).Temperature,pressure,resistivity and reaction time in the process of test were tested,and NGH generation situations and preparation efficiency of different preparation processes were analyzed and compared.And the following research results were obtained.First,in the process of NGH preparation by stirring method,spraying method and bubbling method,respectively,the generated NGH increases slowly and spreads the whole liquid level gradually.Second,inducing period is obvious in the preparation process by the stirring method,but not obvious by the spraying method,the bubbling method and the“three-in-one”method.Third,in the process of NGH preparation by stirring method,spraying method,bubbling method and“three-in-one”method,the resistivity increases as the reaction goes,and its change trend is basically accordant with the NGH preparation rate.Fourth,the preparation cycle of NGH by“three-in-one”method is greatly shorter than that by single preparation method.The preparation time by stirring method,spraying method and bubbling method is about 5.14 times,3.59 times and 3.16 times that of“three-in-one”method respectively.In conclusion,the 1062 L rapid NGH preparation kettle developed in this paper can prepare marine non-diagenetic NGH samples quickly in situ.And compared with single preparation method,“three-in-one”method is much higher in NGH preparation efficiency.
基金Project supported by the subject of“Logging identification and comprehensive evaluation techniques for clastic reservoirs in the Sichuan Basin”subordinate to the National Major Science&Technology Project“Development of large oil/gas fields and coalbed methane”(No.:2008ZX05002-004-003-001).
文摘With complex lithology and reservoir types,as well as high concealment and heterogeneity,tight reservoirs in the Sichuan Basin involve significant uncertainties in gas-water relationship.Since NMR logging can effectively solve problems related to the multiple results of conventional logging operations,it can be deployed for accurate assessment of the properties of formation fluids.Accordingly,different NMR logging activation sets were assessed in accordance with the specific features of tight reservoirs in the basin.With consideration to NMR logging data obtained under different activation sets and testing data of wells,the optimal NMR logging activation set was identified.Moreover,with relaxation characteristics of rocks,gas and water as theoretical foundations,the T_(2) gas and water relaxation characteristics were reviewed to highlight the impacts of porosity,pore sizes,fluid properties and other factors of tight reservoirs on T_(2) horizontal relaxation distribution.According to the research results,D9TWE3 can be seen as the most suitable NMR logging activation set for tight reservoirs in the Sichuan Basin;reservoir tightness is the key influence factor for the distribution of gas/water relaxation in tight clastic reservoirs;generally,in tight sandstone reservoirs,natural gas shows a longer T_(2) relaxation time than water;in fracture-vug type carbonate reservoirs,the right peak of T_(2) distribution spectrum of gas layers is frontal,while the right peak in T_(2) distribution spectrum of water layers is backward.In conclusion,the standards for gas/water relaxation in tight sandstone and carbonate reservoirs in the Sichuan Basin can help effectively determine the physical properties of fluids in tight reservoirs with porosity of 4-10%.Such standards provide reliably technical supports for gas/water identification,reserves estimation and productivity construction in tight reservoirs of the Sichuan Basin.
文摘Field development practices in many shale gas regions(e.g.,the Changning region)have revealed a persistent issue of suboptimal reserve utilization,particularly in areas where the effective drainage width of production wells is less than half the inter-well spacing(typically 400-500 m).To address this,infill drilling has become a widely adopted and effective strategy for enhancing reservoir contact andmobilizing previously untapped reserves.However,this approach has introduced significant inter-well interference,complicating production dynamics and performance evaluation.The two primary challenges hindering efficient deployment of infill wells are:(1)the quantitative assessment of hydraulic and pressure connectivity between infill wells and their associated parent wells,and(2)the accurate estimation of platform-scale Estimated Ultimate Recovery(EUR)following infill implementation.This study presents a novel framework to quantify inter-well connectivity by deriving a material balance equation tailored for shale gas infill well groups,explicitly incorporating gas adsorption and desorption mechanisms.The model simultaneously evaluates formation pressure evolution and crossflow behavior between wells,offering a robust analytical basis for performance prediction.For infill wells intersecting the drainage boundaries of parent wells,EUR is estimated using an analytical model developed for multi-stage hydraulically fractured horizontal wells.Meanwhile,the EUR of the parent wells is obtained by summing their pre-infill EUR with the final inter-well crossflow contribution.
基金supported by the National Science and Technology Major Projects of China(No.2012ZX05018-006-006)the National Natural Science Foundation of China(No.U1262209)
文摘Sedimentary facies is an important factor influencing shale gas accumulation. It not only controlls hydrocarbon generation, but also affects reservoir characteristics and distribution. This paper discusses the Lower Silurian Longmaxi Formation in the south of the Sichuan Basin. Outcrop, core, drilling and logging data identify the sedimentary facies of the formation as continental shelf facies, which is divided into two subfacies： an inner shelf and an outer shelf subfacies. These two subfacies can be further divided into seven microfacies： muddy silty shallow shelf, calcareous silty shallow shelf, muddy limy shallow shelf, storm flow, muddy deep shelf, silty muddy deep shelf and contour current microfacies. Vertical and horizontal distribution of microfacies establishes a sedimentation model of the continental shelf facies. Combined with analization or calculation of geochemical, mineralogical, physical and gas-bearing properties of samples, sedimentary microfacies is evaluated using nine parameters： total organic carbon content, effective shale continuous thickness, vitrinite reflectance, kerogen type, mineral components, porosity, permeability, water saturation and gas content. The evaluation revealed that the most favorable facies for shale gas exploration and development are the muddy deep shelf and part of the silty muddy deep shelf microfacies, with TOC more than 2%, siliceous component over 50%, clay less than 30%, porosity more than 3%, water saturation lower than 40%, gas content greater than 2 m3/t. These results provide a theoretical basis for deciston-making on the most promising areas for shale gas exploration in the Sichuan Basin and for marine shale gas exploration and development in South China.
基金funded by grants from the National Natural Science Foundation of China(No.40930313)the China Geological Survey(No.12120114057701,No.12120114061801 and No.12120114061501)
文摘Diamond,moissanite and a variety of other minerals,similar to those reported from ophiolites in Xizang and northern Russia,have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian Orogenic Belt,north China.The chromitites are small,podiform and vein-like bodies hosted in dunite,clinopyroxene-bearing peridotite,troctolite and gabbro.All of the analysed chromite grains are relatively Al-rich,with Cr^#[100Cr/(Cr+Al)]of about 47-53.Preliminary studies of mainly disseminated chromitite from ore body No.3756 have identified more than 30 mineral species in addition to diamond and moissanite.These include oxides(mostly hematite,magnetite,ruffle,anatase,cassiterite,and quartz),sulfides(pyrite,marcasite and others),silicates(magnesian olivine,enstatite,augite,diopside,uvarovite,pyrope,orthoclase,zircon,sphene,vesuvianite,chlorite and serpentine)and others(e.g.,calcite,monazite,glauberite,iowaite and a range of metallic alloys).This study demonstrates that diamond,moissanite and other exotic minerals can occur in high-Al,as well as high-Cr chromites,and significantly extends the geographic and age range of known diamond-bearing ophiolites.
基金funded by a Major Science and Technology Project of China National Petroleum Corporation(CNPC)entitled Research on Key Technologies for Efficient Production of Overseas Large Carbonate Reservoir”(2023ZZ19-08).
文摘Porous carbonate reservoirs,prevalent in the Middle East,are lithologically dominated by bioclastic limestones,exhibiting high porosity,low permeability,intricate pore structure,and strong heterogeneity.Waterflooding through horizontal wells is commonly used for exploiting these reservoirs.However,challenges persist,such as significant uncertainty and complex operational procedures regarding adjustment effects during the exploitation.The USH reservoir of the Cretaceous D oilfield,Oman exemplifies typical porous carbonate reservoirs.It initially underwent depletion drive using vertical wells,followed by horizontal well waterflooding in the late stage.Currently,the oilfield is confronted with substantial developmental challenges,involving the understanding of residual oil distribution,effective water cut control,and sustaining oil production since it has entered the late development stage.Employing a microscopic visualization displacement system equipped with electrodes,this study elucidated the waterflooding mechanisms and residual oil distribution in the late-stage development of the USH reservoir.The results reveal that the reservoir's vertical stacking patterns act as the main factor affecting the horizontal well waterflooding efficacy.Distinct water flow channels emerge under varying reservoir stacking patterns,with post-waterflooding residual oil predominantly distributed at the reservoir's top and bottom.The oil recovery can be enhanced by adjusting the waterflooding's flow line and intensity.The findings of this study will provide theoretical insights of waterflooding mechanisms and injection-production adjustments for exploiting other porous carbonate reservoirs in the Middle East through horizontal wells.
文摘Romashkino oil field has large oilfield area, small formation dip, many reservoir layers, wide oil-water transition zone and complicated sedimentary environment. Since development, 3 overall development plannings and adjustments of individual block have been established. This achieves a high oil production. However, the recoverable reserves of major oil layer with high production become smaller and smaller and the water cut increases over time, the production ability of oil layer decreases. The development status of oil layer of mining siltstone, oil-water transition zone and oil layer with upswept injected water cannot be changed under present dilute well network condition, because there is no reinforced measurement to water well. This results the low oil production of Romashkino oil field. In order to improve oil production rate and reach the designed oil recovery, Romashkino oil field has been implemented many added cuttings since development. Resent researches about Romashkino oil field show: in later oilfield development stage, sidetrack and lateral drilling horizontal wells technology is very reasonable;formation hydraulic fracturing technology has been widely used in recent years;in tertiary oil recovery, sweep efficiency and flooding efficiency related technologies have been taken. This offers reference and guidance for the effective and reasonable oil field development in later period.
文摘Diamonds, moissanite and a variety of other minerals, similar to those reported from ophiolites in Tibet and northern Russia （Yang et al., 2011）, have recently been discovered in chromitites of the Hegenshan ophiolite of the Central Asian Orogenic Belt. The Hegenshan ophiolite is located in Xilinhaote, Inner Mongolia,
文摘Previously reported in the Mesozonic Tibet and the early Paleozoic Polar Ural,Russia , diamond and other deep minerals are found in ophiolite mantle peridotite chromite that need to be reconsidered ophiolite and chromite traditional understanding of the causes of shallow. The ophiolitic chromitite can be divided two classes, the high-Cr chromitite and high-Al chromitite.
文摘Reservoir pore spaces(incl.pores,fractures and vugs)are too complex to be predicted by use of the traditional interrelationships between the four properties of reservoirs,thus more and more contradictions occur in reservoir evaluation.A great number of case studies were made to reveal the causes of these contradictions and the corresponding solutions were also proposed.For the reservoirs with complex pore spaces,we found four common types of contradictions between porosity and permeability,porosity and water saturation,absolute permeability and effective permeability,and electrical property and hydrocarbon property.These contradictions are mainly caused by variation of pore types,pore-throat sizes and fracture occurrence.On this basis,the concept of geometrical property was presented and methods were discussed for qualitatively or quantitatively describing the geometrical properties of pores,fractures and vugs.The following findings were achieved.(1)For pores,two relationships were established between pores&throat sizes and rock textures,physical property&fluid property,and between pore types and fluid property&logging responses.(2)For fractures,five relationships were established between occurrence and pore texture index(m),radial extension and deep/shallow borehole resistivity,openness and fracture permeability,occurrence and matrix water saturation,and between development index and lithology.(3)For vugs,two relationships were established between size&connectivity and m value&three porosities derived from logging responses(neutron,density and sonic wave),and filling degree and logging responses.The interrelationships between geometrical property,lithology,physical property,fluid property and electrical property can significantly improve the evaluation of complex reservoirs such as carbonates.
文摘Increasing the resolution of seismic data has long been a major topic in seismic exploration.Due to the effect of high-frequency noises,traditional methods could only improve the resolution limitedly.To end this,this paper newly proposed a high-resolution seismic data processing method based on welleseismic combination after summarizing the research status on high resolution.Synthetic record and seismogram are similar in effective signals but dissimilar in noises.Their effective signals are regular and noises are irregular.And they are similar in adjacent frequency.Based on these“three-regularity”characteristics,the relationship between synthetic record and seismogram was established using the neural network algorithm.Then,the corresponding extrapolation algorithm was proposed based on the self-adaptive geological and geophysical variation of multi-layer network structure.And a model was established by virtue of this method and the theoretical simulation was carried out.In addition,it was tested from the aspects of frequency component and amplitude energy recovery,phase correction,regularity elimination and stochastic noise.And the following research results were obtained.First,this new method can extract high-frequency information as much as possible and remain middle and low-frequency effective information while eliminating the noises.Second,in this method,the idea of traditional methods to denoisefirst and then expand frequency is changed completely and the limitation of traditional methods is broken.It establishes the idea of expanding frequency and denoising simultaneously and increases the resolution to the uttermost.Third,this new method has been applied to a variety of reservoir descriptions and the high-resolution processing results have been improved significantly in precision and accuracy.
基金Project supported by the Science and Technology Project of CNPC Chuanqing Drilling Engineering Co.,Ltd“Element logging features of key horizons and application in SichuaneChongqing gas provinces”(No.:CQ2014B-14-1-1).
文摘With the popularization and application of fast drilling technology in Sichuan-Chongqing gas provinces,the returned cuttings are fine and even powdered,so the traditional cutting lithology identification methods are not applicable any longer.In this paper,qualitative lithology identification and quantitative interpretation based on element logging were conducted on the key oil and gas bearing layers in this area according to the principle of elemental geochemistry.The study results show that:(1)different lithologies can be identified easily because of their different element logging characteristics.For example,basalts have the element characteristics of 0.35<Fe/Si<0.55 and Ca/(Na+K)<4.00,while sedimentary rocks have Fe/Si<0.35 or>0.55.(2)Clastic rocks,carbonate rocks,sulphate and transition rocks in the category of sedimentary rocks can be identified based on the element combination of(Al+Si+Fe)and(Ca+Mg+S).Among them,clastic rocks have(Al+Si+Fe)>31%,carbonate rocks have(Al+Si+Fe)<8%and(Ca+Mg+S)<36%,and sulphate rocks have(Al+Si+Fe)<5%and(Ca+Mg+S)>36%.(3)Then,based on the element combination of(Si+K+Ca)tSi/Al and(Al+Si+Fe+K)t(Ca+S)/Mg,sandstone,mudstone(shale),gypsum,dolomite,limestone and transition rocks can be identified.Finally,a qualitative identification chart and a set of quantitative interpretation software of element logging on key horizons in Sichuan-Chongqing gas provinces were developed to make this method convenient for field application.This method was applied on site in ten wells(such as Well MX207)in Sichuan-Chongqing gas provinces.It is indicated that the coincidence rate of lithology identification is in the range of 88.75-95.22%(averaging 92.42%).Obviously,it can satisfy the requirements of fast lithology identification while drilling of key oil and gas horizons in Sichuan-Chongqing gas provinces.
基金supported by the National Natural Science Foundation of China(Grant No.42173038)the PetroChina s for Basic Scientific Research and Strategic Technology Reserves(Grant No.2023D-5008-02)the Fundamental Research Funds for the Central Universities-Cemac GeoX Interdisciplinary Program(Grant No.2024ZD04)。
文摘Hydrocarbon evolution is a crucial part of the global organic carbon cycle,and controls the distribution of hydrocarbon phases within the Earth's crust.However,the pathway and boundary conditions of hydrocarbon phase evolution remain poorly constrained due to the lack of reliable geological records.Here we present a unique assemblage of sequentially trapped oil,wet gas(C_(1)/∑C_(1-5)=0.74±0.03-0.91±0.01)and dry gas(C_(1)/∑C_(1-5)=0.96±0.01-1)fluid inclusions from the Ediacaran dolomite reservoirs in the central Sichuan Basin,South China,which constrains the pathway and conditions of in situ hydrocarbon phase evolution.Notably,the early trapped oil inclusions(~247 Ma)exhibit abnormally low maturity(0.75%-0.97%vs.2.67%-2.79%VRE for reservoir pyrobitumen).The formation of these oil inclusions is attributed to three key processes:(1)pressure buildup during inclusion oil cracking;(2)leakage of volatile components through decrepitation;and(3)retention of heavy hydrocarbons in the re-equilibrated oil inclusions.In contrast,the reservoir oil underwent in situ cracking and was successively transformed to wet gas(~197 Ma)and dry gas(~116 Ma)with increasing temperature.During this process,a selfregulating mechanism of fluid overpressurization(e.g.,59-86 MPa in 197-182 Ma and 114-151 MPa in 116-109 Ma)and pressure release was identified to facilitate the hydrocarbon-bearing fluid migration.Integration of coexisting aqueous inclusion analyses with burial history reconstruction refines the oil(≤156℃)and wet gas(≤213℃)preservation windows,respectively,in prolonged heating reservoirs.These findings shed new light on hydrocarbon evolution and petroleum exploration in deep strata.
基金Project supported by the National Key Basic Research Development Program of China(973 Program,Grant No.2014CB239205)
文摘Most researches of the threshold pressure gradient in tight gas reservoirs are experimental and mainly focus on the transient pressure response, without paying much attention to the transient rate decline. This paper establishes a dual-porosity rate transient decline model for the horizontal well with consideration of the threshold pressure gradient, which represents the non-Darcy flow in a fracture system. The solution is obtained by employing the Laplace transform and the orthogonal transform. The bi-logarithmic type curves of the dimensionless production rate and derivative are plotted by the Stehfest numerical inversion method. Seven different flow regimes are identified and the effects of the influence factors such as the threshold pressure gradient, the elastic storativity ratio, and the cross flow coefficient are discussed. The presented research could interpret the production behavior more accurately and effectively for tight gas reservoirs.
