Contents of Natural Gas Geoscience, No.2, 2017
For the lack of homogeneity and the same porosity conditions permeability diverges obviously in different blocks or different layers.Considering various influencing factors on complex reservoir’s permeability,using the traditional permeability model to improve flowing unit index methods,classification model of the permeability in the Yinggehai Basin was set up.And put forward the selection by Gassmann fluid replacement after the correction of longitudinal wave time difference,porosity and shale content three logging curve,Fisher discriminant analysis is used to establish a new method of reservoir permeability type discriminant standard.Application of the discriminant method in A1,A2 gasfields of Yinggehai Basin,shows that distinguishing the permeability’s type using this method is very accurate.
Referred to the new recognition from petroleum exploration of the Sinian to Cambrian in South China,it could be considered that the distribution of the early Cambrian source rocks was controlled by the palaeo-geomorphology at the end of Neoproterozoic in the Tarim Basin.Based on the zircon U-Pb dating of pyroclastic rock samples from the clastic rock stratum under the bottom of Cambrian carbonate rocks,the stratigraphic correlation of the Sinian to Cambrian was conducted to build the palaeo-geomorphology framework at the end of Neoproterozoic in Tarim Basin.Lastly,according to the development mode of source rocks at the beginning of Cambrian,the distribution of source rocks was predicted initially through the division of seismic facies.The youngest zircon concordia age of pyroclastic rocks from the bottom of Well Tong 1 is 707±8Ma.It was revealed by the strata framework of the Sinian to Cambrian,the palaeo-geomorphology at the end of Neoproterozoic in Tarim Basin was characterized by an uplift highland in Bachu-Tazhong area,the south north high-low,and the west is higher than the east.The distribution of source rocks in the bottom of the Cambrian on the palaeo-platform and slopes was coincident with the Upper Sinian dolomite basically.But the contemporaneous sediment happened to be absent or changed in sedimentary facies on the uplift and its edges.From the seismic facies of the strata under the bottom of Cambrian,it could be concluded that source rocks in the type of the Xishanbraque Group (∈1xs) was limited in the Manjiaer Depression,while the source rocks in the type of the Yuertusi Group (∈1y) are widely distributed in south of Tabei Uplift,east Awat Depression,and even the Maigt Slope.However,among the west Awat Depression and western Tanguzibasi Depression,and the middle area of the Bachu-Tazhong Uplift,the contemporaneous source rocks may have changed into sedimentary facies of tidal flat and lagoon,instead of deep shelf.
Systematically illuminating the controlling factors on fracture development in the tight sandstone reservoirs is the key basis to accurately predict the fracture distribution.Fractures in the tight sandstone reservoirs of Kuqa foreland basin are quantitatively characterized,and a systematic research on the fracture distribution and controlling factors is carried out.Tectonic fractures are dominant in the tight sandstone reservoirs,and their development was controlled by inherent (e.g.,lithology,mechanical stratigraphy,sedimentary micro-facies and diagenesis facies) and external (structural position and overpressure) factors.Rocks with high content of brittle minerals,fine grain size,low porosity and well sorting are conducive to the development of fractures.Fractures often develop in the competent rocks and their height is equivalent to the thickness of mechanical layer.Sedimentary micro-facies with thick cumulative deposition thickness,thin single layer and fine granularity are the favorable area for fracture development.Diagenesis facies with dense compaction and cementation are also areas favorable for fracture development.Vicinity of fault and hinge of fold are area of local stress concentration,thus the fracture density increased significantly.The existence of overpressure promotes the failure of rocks.
The reservoir of gasfield A,which located in Kuqa Depression of Tarim Basin,has features of large burial depth,and belongs to fractured tight gas reservoir.As the pore-throat is small and the pore structure is complex,it’s difficult to do the pore throat structure characterization by conventional methods.In this paper,lots of advanced technologies,such as LSCM,FESEM,Micro-CT,Nitrogen adsorption and NMR,are used to do the pore throat structure characterization.It’s found for the first time that,the reservoir of gasfield A has microscopic characteristic of tri-media,which contain large pore-throat medium,small pore-throat medium and fractures.The volume of large pore-throat medium approximately equals to the volume of small pore-throat medium,but large pore-throat medium’s contribution to the matrix permeability accounted for 95%.The pore and throat collocations are mainly big pore-coarse throat,small pore-fine throat,and small pore-coarse throat are secondary.Absolute fracture porosity is only about 0.01%-0.5%,1.8%-2.8% of total reservoir porosity,but fracture is main seepage channel of reservoir,the permeability of fractured samples is about 10 times or 100 times of samples without fracture.Based on the research of reservoir characteristics above,the conceptual model of tri-media reservoir is established,which can interpret the reservoir seepage characteristics well.The research idea in this paper will be helpful to other similar reservoir.
In recent years,important breakthrough progress and discovery has been made in exploration of petroleum from deep reservoirs of E23 in western Qaidam Basin.Based on core observation,petrographic and structural microscopic characteristics analysis,and geochemical analysis,the characteristics and major factors controlling the development of dolomite reservoirs in the Yingxi area in Qaidam Basin are studied.Dolomicrite was the main effective reservoir rock of E23 in the Yingxi region,whose physical characteristics are “low porosity-extra low permeability”.The reservoir spaces of the dolomite are mainly intergranular pore,but including some micro-cracks.Oil and gas can be produced stably in the Yingxi Oilfield because most oil and gas are preserved in these “small size-large quantity” pores.Research results of the geochemical characteristics of reservoir show that the dolomite is penecontemporaneous metasomatic type which formed in the salty conditions.Main evidence includes:(1)micro pore structure characteristics,(2)high Ca/Mg molar ratio of no ideal components,(3)low content of “Mn” element geochemical characteristics,(4)“carbon negative-oxygen positive” isotope geochemistry and the low temperature characteristics reflected by it,(5)low degree of order structure which is caused by the rapid nucleation and crystallization unstable environment.The shrinkage intergranular pores were formed by ion exchange in the crystal lattice in the special salty environment,and its pore size is controlled by the abundance of Mg2+ at that time.Therefore,the physical property of the reservoir is indirectly controlled by the paleo salinity.These intergranular pores have a strong ability to resist compaction and they can still be preserved in the deep,ultra deep strata.The origin model of dolomite determines its wide distribution in the plane.So the research findings expanded a new exploration field about lacustrine dolomite in western Qaidam whether in the plane distribution or in depth.
Lower limits of porosity and permeability for oil accumulations can provide major parameters for the oiliness evaluation of tight sandstone reservoir,and important guidance for exploration discovery of tight oil of Ordos Basin which has big exploration potential. Many data including mud logging,log data,well test and production test,physical property,mercury intrusion,fluid inclusion,thin section examination,SEM and so on were applied to determine porosity and permeability cutoffs of effective reservoir in the Chang 7 member,southeastern Shaanbei Slope,Ordos Basin,and critical accumulation period. By adding the loss of porosity after oil accumulation to current lower limit value of effective reservoir,lower limits of porosity and permeability for tight oil accumulations in the Chang 7 member,southeastern Shaanbei Slope,Ordos Basin were determined. The results show that the lower limit values of porosity and permeability of effective reservoir are 5% and 0.038×10-3μm2. The critical accumulation periods are mainly the mid-late stage of Early Cretaceous. The physical properties of Chang 7 member reservoir are different between the critical accumulation period and nowadays,and the average differences of porosity between the two ages in the Ⅳa,Ⅳb and Ⅴ reservoir type are 5.15%,3.46%,2.32%,respectively. The physical property values of Ⅳb and Ⅴ reservoir type are nearly the current lower limit value of effective reservoir,the average differences of porosity of the two reservoir type between the critical accumulation period and nowadays are 2.79%,and then the lower limit value of porosity and permeability of oil accumulations of Chang 7 member in the study area are 7.79% and 0.10×10-3μm2.
Mid-deep strata with high temperature and overpressure of Dongfang area in Yinggehai Basin has become the focus of oil and gas exploration in recent years,and significant exploration breakthrough was made in the first section of Huangliu Formation.However,characteristics of high resolution sequence stratigraphy,reservoir sedimentary microfacies and evolution and subtle trap in it need to be revealed.Based on substantial cores,drilling,well logging and 3-D seismic data,high resolution sequence stratigraphy framework of the first section in Huangliu Formation of Dongfang area was constructed,and the types,sedimentary characteristics and evolution of sedimentary microfacies in different sequence units were investigated.In addition,characteristics and distribution of the favorable reservoir as well as subtle traps were revealed.And finally,the exploration direction of subtle reservoir in this area was discussed.The results show that the first section of Huangliu Formation can be divided into five parasequence sets,they are Ps1,Ps2,Ps3,Ps4 and Ps5 from bottom to top in the order.Ps1,Ps2 and Ps3 all belong to lowstand system tract,while Ps4 and Ps5 correspond to transgressive system tract and highstand system tract,respectively.There are neritic turbidite fan and neritic facies in the lowstand system tract.The neritic turbidite fan consists of two kinds of subfacies-middle fan and outer fan,and the former is predominant which includes three kinds of microfacies-turbidite channel,inter channel deposition and natural levee,while in both of transgressive system tract and highstand system tract shelf mud and neritic sand bar developed.Turbidite channel sandstone is the primary reservoir in Huangliu Formation of Dongfang area,and the lowstand system tract is the most important exploration strata.There are mainly structural-lithologic composite reservoirs in the diapiric structure zone,and updip pinchout lithologic reservoirs in the wings of diapiric structure zone,and lenticular sandstone lithologic reservoirs in western Dongfang area which is non-diapiric structure zone.
The NW-trending pre-existing faults and the NE-trending early faults controlled the structural evolution of the Shaleitian uplift margin.According to the characteristics of the main faults,the combination of the main faults,the early synsedimentary faults and the companion faults,Shaleitian uplift margin accommodates the following six kinds of the Paleogene faulting structure styles:concordant fault terrace gentle-slope margin,major low-angle faulted gentle-slope margin,straight normal faulted gentle-slope margin,listric normal faulted steep-slope margin,ramp-flat normal faulted steep-slope margin and platy normal faulted steep-slope margin.Different types of faulted slope-breaks and palaeogeomorphology formed by fault structural styles with early valley developed on the uplift controlled the input and distribution of material source and resulted in different types of raised edge sedimentary filling characteristics.As a result,the plane distribution and vertical evolution of sedimentary facies belts from the uplift to the depression have certain regularity.In concordant fault terrace gentle-slope margin,the low fan-delta developed in early period and the thick braided delta front developed in later period in control of the early basin-margin slope.The main fault which separates Shaleitian uplift and the adjacent depression controlled the development of the high fan-delta in early period and the braided delta in later period.The syndepositional fault which developed on the major low-angle normal fault controlled the deposition of the low fan delta and turbidite fan in the Es3 member and then developed braided river delta and shore shallow lake in the major low-angle faulted gentle-slope margin.The transgressive and high braided river deltas developed in Shahejie Formation in the straight normal faulted gentle-slope margin,the thick braided deltas front developed below the slope break and the delta plain and small filled valleys developed on the slope break in Dongying Formation.The sedimentary filling has a layered structure in the vertical direction in the edge of the steep slope.From early to late stage,the early alluvial fan or fan delta facies evolved into braided river delta,the steep slope controls the development of the low fan delta,and the delta plain and small filled valleys developed on the slope break.
Melut Basin has abundant petroleum resources as a Central Africa passive rift basin and developed two typically highly sandy formations.The regional highly sandy formation,which is made up of regional thick sandstone of Yabus and Samma Formations and regional mudstone of Adar Formation of Paleogene,is the key reservoir-caprock assemblage and formed all kinds of antithetic faulted blocks and faulted-nose structural reservoirs.By contrast,the local highly sandy formation of Galhak Formation of Upper Cretaceous,which is close to source rock and interbedded by sandstone and mudstone,is a new reservoir-caprock assemblage and exploration target layer for seeking structure-lithology and lithology-stratigraphy reservoirs in the mid-late stage of basin exploration.By deeply studying the oil reservoir character,enrichment rule,reservoir evaluation and exploration method of the highly sandy formation of Galhak Formation,the research firstly revealed that the flooding mudstone controlled the oil reservoir formation,and the distributary channel sandstones of inner braided delta front controlled HC enrichment.That is,the flooding mudstone is the key controlling factor on hydrocarbon pool formation,the high-porosity and thick sandstone is the reservoir condition and the inner braided delta front is the favorable sedimentary facies zone for developing high production layers of Galhak Formation.Moreover,the paper proved that the fine division and evaluation based on the identification and correlation of flooding mudstones can improve the study scale and evaluation accuracy for highly sandy formation.And the integrated approach of judging oil & water layers based on well logging,mud logging and reservoir geological conditions can more accurately understand oil-water contact and reservoir characteristics for the complicated faulted block reservoirs of thick and highly sandy formations.The study upgraded the exploration potential of highly sandy formations interbedded by sandstone and mudstone,and expanded exploration space of Melut Basin,and will have an important impact on highly sandy formations exploration in the similar passive rift basins in Central and Western Africa.
In order to research the effect of particle size on adsorption properties of shale,shale samples rich in gases are collected from the Silurian Longmaxi in the Sichuan Basin and four types of coal specimens are made.The grain diameters of these specimens are within the ranges of 1 700-3 350μm,850-1000μm,180-250μm and 106-131μm,respectively.The isothermal adsorption experiments were conducted under the condition of high pressure and high temperature,which are aimed at carrying out further study on the effect of the pore connectivity,specific surface area and roughness on the methane adsorption and the effect of the sensitivity of particle size.Results showed that methane adsorption capacity were negatively related to the particle size,the value of Langmuir volume decreased after showing sharp increase and then increased with the particle size going down.Specific surface area increased from 6.09m2/g to 8.81m2/g,while the particle size from 1 700-3 350μm down to 180-250μm.Furthermore,both value of pore volume and the rate of contribution on specific surface area whose diameter is less than 5nm increased from 57.94% to 80.36% and from 74.34% to 92.85%,respectively.It could be safely drawn out the conclusion that,(1)The pore connectivity got to be better with the decrease of particle size,which is actually conducive to improve the adsorption ability motivated by removing obstacles and optimizing path for the mass-transfer efficiency and methane adsorption of shale.(2)The smaller the particle size,the higher the quantity of the close pore which is exposed by crushing and the mesopore whose diameter is between 2nm and 5nm,pore volume and specific surface area has been greatly improved,the methane molecules have greater adsorption space to produce more of the adsorption quantity.(3)Considering the fact that the extent of pore roughness performed negative relationship to particle size,more considerable pore,organic and clay minerals are exposed while the particle size decreases,which makes the specific surface area increase in large region,as a consequence,supplying more high energy absorption sites on the pore surface are actually helpful to improve the adsorption ability.
Gas permeability model of natural fracture network in shale formation is one of the emphases for shale gas development research.In this paper,we adopted fractal binary tree capillary bundle model to simulate natural fracture network in formation,and got gas spherical oriented flow function in binary tree fractal model based on Hagen-Poiseulle equation.We analyzed rectangle,triangle,oval fracture section and facture structure parameters such as fracture bifurcation angle θ,fracture fractal dimension Df,caplillary length coefficient α,rectangle fracture section width-height ratio x1,oval fracture section major axis-minor axis ratio x3 influence on fracture fractal permeability Kf.Fracture fractal permeability Kf sorts by values in descending order is circle tube model,oval section model,rectangle section model,triangle section model.Kf increases as Df increases; Kf shows a non-monotonous behavior with the increase and then decrease of θ and Kf gets the minimal value when θ equals 90°;Kf decreases as α,x3 increase;Kf increases at first then deceases as rectangle fracture section width-height ratio x1increases and Kf gets maximum value when x1 equals to 1.
With the rapid economic development and sustained growth in demand for clean energy,the contradiction of China’s energy supply shortage is increasingly highlighted.The wild distribution of China’s coal-bed methane (CBM) resources accelerates the exploration and development of CBM.It is the need of national energy security,and conforms to the new energy strategy of CNPC.Because the biggest difference between the CBM and the conventional gas is that the gas adsorption in coal pore surface,and CBM has the distinctive feature of reservoir distribution characteristics and controlling factors,compared with the conventional natural gas exploration,the exploration aiming for CBM reservoir physical & gas-bearing property,has higher requirement on data quality,prediction method and information content.Basic research on the rock physics is the starting point and foothold of CBM prediction method.Considering the diversity of sedimentary coal seam in china,by selecting the coal sample with different coal rank,different coal rock and different coal quality,through the laboratory testing parameters and actual drilling data analysis,we confirmed that the modulus properties are more sensitive to the tons of coal containing gas,and between the p-wave velocity and density,the density is more sensitive to the tons of coal containing gas than P-wave velocity.According to this,we established the CBM seismic three-parameter elastic modulus (lame constant relative variation,shear modulus relative variation,density relative variation) inversion method.Through the instance of Southern Sichuan,we proved that the relative modulus variation can effectively predict the enrichment of CBM enrichment region.Prediction of 5 wells agrees with the production,which improve the success rate of the deployment CBM well.
Based on a large number of fracturing data at home and abroad,through theoretical and experimental data,the influences of different parameters on hydraulic fracture formation and extension are studied.The parameters include the difference coefficient of horizontal principal stress within layers,the difference of minimum horizontal principal stress between layers,the rock mechanics parameters,the difference coefficient of internal coal and rock fracture pressures and the properties of rock interface.According to field fracturing and production data,the influences of geological and fracturing engineering parameters on gas production are analyzed,such as the earth stress conditions,the fracturing technology,the volume of fracturing fluid,the amount of sand,the system of fracturing fluid,the interval of fracturing perforation and the technology of secondary fracturing,all of which have important influences on the production.Through the optimization of the technology,the reasonable fracturing technology and parameters are offered for Hancheng mining area.The ideal effects have been achieved in the practical field application.This work provides a theoretical basis and a reference index for the implementation of the middle-high rank coal reservoirs fracturing technology in China.
Numerical simulation is a significantly important method for the dynamic analysis of coal-bed methane reservoir and gas production.This paper proposed a stress-seepage hydro-mechanical model for coal-bed methane reservoir that was considered as dual permeability media of matrix pore and fracture.At the same time,the influence of the deformation of coal-bed on the gas seepage field was considered.The model involved the effects of coal-bed methane’s adsorption and desorption,the coupling of stress-seepage,and other factors on the coal bed methane extraction.SPH (Smoothed Particles Hydrodynamics) method was used to discretize the governing equations,and thus corresponding SPH code was made.A numerical example was presented using the proposed model and field coal bed parameters.The model is used to solve and analyze the process of coal bed methane desorption and the change of permeability.The SPH method can be applied to the study of coalbed methane desorption and seepage process and the dynamic analysis of coalbed gas reservoir.Results show that the matrix permeability and fracture permeability are influenced obviously by effective stress.Considering the adsorption and desorption of coal-bed methane are more realistic in the process of the coal-bed methane seepage,which is needed in the reasonable estimation of the amount of gas emission during the actual gas production process.
The maturity of the Ordovician oils from Tahe Oilfield of Tarim Basin,NW China was assessed by various maturity parameters,such as biomarkers,aromatic parameters and diamondoid parameters.Both Ts/(Ts+Tm) and C29Ts/(C29H+C29Ts) values indicated that the maturity of oils has not reached the condensates stages,which is in consistent with the maturity obtained by MPI-1.However the diamondoid maturity suggested that the oil maturity is in the range of 1.1%-1.6% RO,which is obviously higher than that of the maturity obtained by biomarker and MPI-1.This discrepancy of maturity may reflect the Ordovician reservoir have multiple filling history.The concentration of methyldiamantane suggested that the methyldiamantane concentration of oils is scattered and increase slowly when Ts/(Ts+Tm) value is lower than 0.55,and the content increases rapidly when Ts/(Ts+Tm) value is higher than 0.55.Based on the diamondoid concentration of oils from different age,it is proposed that the diamondoid baseline is about 15×10-6 in the Tahe Oilfield.In general,the concentration of methyldiamantane of most Ordovician oils ranges from 4×10-6 to 35×10-6,suggesting that the degree of oil-cracking is lower than 50% and the deep Ordovician has the potential of oil exploration.The distribution of the concentration of methyldiamantane is characterized by high in east,low in west,high in south and low in north,suggesting two migration pathways are from south to north, from east to west, respectively, which is consistent to the migration results obtained from oil density and maturity parameters such as Ts/(Ts+Tm).
Though no light alkenes existed in oil and gas reservoirs,light alkenes including C2H4 and C3 H6 often occur in the soil gas over oil and gas fields,accompanied with high concentration of C1-C5 alkanes.The exploration cases in Linnan Oilfield,Huimin Sag of Jiyang Depression,China and Teapot Dome Oilfield,Wyoming,USA suggest that these light alkenes are not derived from in-situ surface organic matters.In order to explain the origins of these light alkenes in the soil gas to reinforce the foundation of Surface Geochemistry Exploration (SGE),a simulation experiment was conducted to simulate the surface geochemical characteristics of hydrocarbons micro-seeping vertically from a hydrocarbon reservoir.The experimental results are in accord with that in oilfield.It is proved that these light alkenes come from the surface microbial evolution of the light alkanes micro-seeping from the hydrocarbon reservoirs.The above results illustrate the forming mechanisms of the surface light alkenes anomalies over oil and gas fields and enhance the credibility of the light hydrocarbon anomalies in SGE.It is also provided that the light alkenes can be a new indicator in SGE on the basis of theory and practice.
In this paper,the influences of iron-bearing minerals on gas generation and isotopic fractionation of organic matters was studied by hydrous pyrolysis of a type-II kerogen of low maturity in the presence or absence of Fe3O4.Quantitative determination of the gas products generated during the experiments indicated that the addition of Fe3O4 would lower the yields of gaseous hydrocarbons,H2 and H2S,whereas exerting little influence on the yields of CO2.Carbon isotopic analysis revealed that when Fe3O4 is added to the reaction system,the carbon isotope of methane was not significantly affected,however,the isotopic values of both ethane and propone showed increase to different degrees.In contrast,the hydrogen isotopic values of the gaseous products in the presence of iron-bearing mineral were more depleted,and the reduction of methane and the ethane were 5‰-50‰ and 24‰-40‰,respectively.Likewise,the isotopic analysis of the residues showed similar trends with the gas products,which is the lighter hydrogen isotope values in the experiments with Fe3O4,and there are no obvious differences of carbon isotope with or without Fe3O4.Additionally,H/C elemental ratios of the residues decreased at a slower rate and exhibited higher values in the cases of iron-bearing mineral added experiments.The above results indicated that different reaction systems are of different reacting mechanisms.When Fe3O4 is absent,the reaction system operates in the cationic reacting mode.However,when Fe3O4 is added to the reaction system,cationic reactions were inhibited,thus resulting in the reduction of gas generation,and there exists indirect hydrogenation controlled by the presence of hydrogen.
With the increasing difficulty of exploration,the accuracy of the time-frequency resolution of wavelet transform has been difficult to meet the requirements of the actual exploration targets,which needs to explore a higher resolution time-frequency analysis method.The synchrosqueezing wavelet transform (SWT) can obtain time-frequency resolution better than the wavelet transform by squeezing and reconstructing complex coefficient spectra in frequency direction.And it also has reversibility and anti-noise property.The simulation results show that the synchrosqueezing wavelet transform has better accuracy in characterizing the time-frequency characteristics of the signal.And in the analysis of the actual seismic data,the frequency division process of the synchrosqueezing wavelet transform is applied to process the thin gas-bearing reservoir seismic data.Where the low frequency appears obvious anomalies,and the lower frequency is,the more obvious anomalies are.So the reservoir is predicted effectively.
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