Tight sandstone gas has become a focus of the global unconventional natural gas exploration.It is widely distributed in China.Until recently, Ordos and Sichuan basins have achieved the large-scale exploitation.Tight sandstone gas in China has mainly three types, including slop type, structure type and depression type.The tight sandstone reservoirs are mainly sourced by coal-measure rocks, and charged continually.The widespread source rocks and reservoirs interbed.Therefore, the gas can migrate vertically from source to adjacent reservoir.The intimate contact of source and reservoir forms the large-scale gas-bearing area, with“sweet spots” locally enrichment.The favorable exploration area of tight sand gas in China is 3.2×105 km2，with recoverable resources about(8～11)×1012m3.Currently, China has comparatively mature technology of the exploration and development of tight sandstone gas, having the conditions of accelerating the developing pace.Therefore, tight sandstone gas will play an important role in the future natural gas development in China.
The middle Ordovician Majiagou Formation,which mainly consists of micritic dolomite and limestone, and evaporates,deposited in a restricted epeiric carbonate platform with high salinity in the Ordos basin,China. A part of rocks were reformed into karst breccias by karstification.The δ18Oandδ13Cvalues for the whole rocks or hand\|picked carbonate rocks in the middle Ordovician Majiagou Formation range from -16.0‰ to -1.9‰ (average value =-8.5‰,VPDB) and from -16.1‰ to 4.83‰ (average value=0.90‰,VPDB),respectively.The δ18O and δ13C values for the laser\|micro sampled carbonates in the Majiagou Formation range from -15.8‰ to -0.8‰ (average value=-7.7‰,VPDB) and from -12.4‰ to 5.77‰ (average value=-0.15‰,VPDB),respectively.Although the data measured by two sampling methods do not show the difference, the data measured by the later method give more information about different carbonate components.The originally deposited calcite and limestone have the maximum δ18Ovalue of -5.8‰(VPDB),indicating that it would be δ18O values of original marine carbonates.This result is consistent with the published results of global stable isotope sequence.The means and minimums of the δ18O values for the originally deposited calcite and limestone are low due to meteoric leaching and burial diagenesis.The δ18O values of calcite cements filled in the dissolution pores are generally low under action of meteoric leaching and high temperature burial.The maximum of δ18O values for the originally deposited dolomite formed in the restricted environments with high salinity is obviously higher than that of the originally deposited calcite and limestone.The δ18O values for the dolomite filled in pores are generally low since its formation time was later.The maximum increase δ13Cvalues for the middle Ordovician marine carbonate in Ordos basin would be related to the increase of δ13C value for global marine water during late Ordovician,since the δ13C values for marine water in middle and later Ordovician onset increase.The lowδ13C values for a part of samples are related with the organic carbon mixing.
After sedimentary facies and trace elements geochemistry of Permian source rock in Shifang profile of the western Sichuan province is illustrated,we find out that different sedimentary facies have various characteristics of trace elements.The enrichment of nutritional elements such as P,Ba,Cr,Ni,Cu and Zn,indicates the high biological productivity.The ratios of V/(V+Ni),V/Cr and Sr/Ba take a indicator for organic matter preservation.The geochemistry of trace element is consistent with organic matters abundance,sedimentary facies,transgression and regression cycle,organic matter preservation,and organism flourishing.Therefore,the geochemistry of trace element is a potential parameter for distinguishing sedimentary facies.
According to abundance and type of organic matter and its thermal maturity,we consider that the upper and lower sections of lower Ganchaigou Formation belonged to good and better source rock.The biomarker features of n-alkenes for source rocks show an even-to-odd (15-19) and odd\|to\|even (25-29) predominance.Terpenoids are characterized as high γ-and tricyclic diterpene,low γ-and tricyclic diterpene,low abundance of C34and C35hopanes,and C27>C29 or C29>C27 for steranes.All of geochemical parameters suggest that the organic matter was derived from aquatic organisms and higher plants in the transition zone between deep and shallow lacustrine depositional settings.It should be noted that the occurrence of one terphenyl compounds in the aromatic hydrocarbons from 5 source rocks (Lücan 1 well) sampling at different depth,and the relative abundance of each isomers is positively related to thermal maturity,20S/(20S+20R) ratio of C29 steranes,and RO values.So the relative abundance of each isomer would be a potential parameter for indicating thermal maturity of organic matter.
The geochemistry of the Paleogene source rock in the M block of south Sumatra basin is studied in this paper.The results show that the total organic content of Paleogene source rock in this block is high.Vitrinite is the dominant micro-petrological unit,sapropelic and liptinite is secondary,and inertinite is little.Kerogen type is Ⅱ1 ,mixing of Ⅱ1 and Ⅱ2,Ⅱ2,and Ⅲ.The source rocks have ability to produce oil or gas.The values of RO range from 0.44% to 0.71%,with average value of 0.62%.The thermal maturity indicates that source rock is at immature and mature stage.The distribution of oil at the top and gas at bottom occurs vertically in this block due to type of organic matter and thermal maturity of source rock.So we propose that the shallow layer for oil and deep zone for gas would be paid to attention.
Yabei sag lies in the western part of northern depression of Qiongdongnan basin in the continental margin of South China Sea,covering an area of nearly 3 000km2.After the sag was rifted in Paleogene,it accepted the Eocene continental formation,early Oligocene Yacheng transitional formation and later Oligocene Lingshui marine formation.Yacheng Formation is the most important source rock by obsevasing the drilled souce rocks and measuring the gas geochemerstry and making the source-gas correlation in the basin.Coal measure and carbonaceous mudstone are the most important components of source rock,and the drilled wells indicate that they occur from Yacheng-3,Yacheng-2 and Yacheng-1.Rockcores of shallow water area in the Yabei sag shows that the Yacheng-3 formation was formed in the fan-deta,braided stream,the Yacheng-2 was in lagoon,and the Yacheng-1 was in tidal flat facies.The coal meaure and carbonaceous mudstone are distributed mostly in the formations of Yacheng-1 and Yacheng-3.The Yacheng-3 in the Yabei sag shows the chaos seismic faices,the Yacheng-2 exhibits weak amplitude and low frequency and well continuation seismic facies,and the Yacheng-1 is strong amplitude,strong continuation and low frequency.It is good conrespond between seimic facies and sedimentary facies.The sedimentary facies maps drawn by rockcorea,well logging and seismics suggest that the Yacheng-3 was mostly in braided delta,the Yacheng-2 in the lagoon extended a lot,and the Yacheng-1 was mostly in tidal flat.Coal is mostly distributed in the slope of sag in braided delta and tidal flat and second along steep slope in fan-delta and tidal flat;dark mudstone is mainly in the deep area of lagoon.So,we consider that the greater distribution of coal in south slope of Yabei sag and dark lagoon facies,and the giant gas potential in shallow water area of Qiongdongnan basin is strong.
It is a typical sedimentary basin of both high temperature and overpressure in the Qiongdongnan basin.Based on collecting the literatures from foreign or our country as well as previous research achievements related to overpressure, we conclude the research progress of pressure prediction in the continental slope area, and the distribution characteristics of overpressure in the basin.In combination with logging data, test pressure data, and geological background, physical geography and geochemistry, we discuss the overpressure genesis and its main formation mechanism in the basin.It is an important geological condition for overpressure formation to be rapid subsidence and high sedimentation rate, especially higher sedimentation rate in the western area than other area of the basin which results in the thick sediments with a certain thickness of mudstone since the Neotectonic event (5.3Ma).Overpressure formation in the basin is mainly resulted from rapid subsidence of low permeability sediments and disequilibrium compaction of overlying strata.Thus, it is essential for the overpressure formation to be imbalance between supply and discharge of pore fluid in the Qiongdongnan basin.Meanwhile, the overpressure is exacerbated further by gas generation and thermal expansion of fluid.So, it is significant in theoretical and practical aspects to oil and gas exploration and development in the Qiongdongnan basin.
By means of microscopic observation of a lot of petrographic thin section as well as diagenetic stage of classification signs,we consider that the diagenetic stages of Huagang Formation sandstone in the study area would be at the late diagenetic stage B.We use optical microscopy,scanning electron microscopy,electron microprobe and X-ray to analysis species and composition of authigenic mineral,rock structure,types and structural characteristics of porosity for the Huagang Formation reservoir sandstone in the Xihu sag,East China Sea Shelf basin,and identify acidic and alkaline diagenetic environments.The acidic diagenetic environment is characterized as dissolution of feldspar+secondary stripping holes+kaolinite+quartz characterized by increased secondary and the alkaline diagenetic environments is the dissolution of quartz+advanced filling and metasomatic ferrous carbonate.The main evolution mechanism of acid and alkaline diagenetic environments is controlled by the unary and binary water-soluble acid and phenol which are generated by thermal cracking of oxygen-containing carboxyl and phenol of nuclear periphery kerogen.At middle diagenetic stage A period and RO ranging from 0.5% to 1.3%,the unary and binary organic acid is generated by removing carboxyl from organic matter,associated with CO2 formation which will make pore fluid become acidic.When the thermal maturity of source rock increases,organic acid will be damaged,the action of removing carboxyl become weak and CO2 content decrease,the pore fluid properties change gradually from acidic to alkaline.
Tongnan area is located in the gentle structure of central Sichuan basin.T3x2 reservoirs in the Tongnan area are characterized as low porosity,low permeability,high heterogeneity,and high water saturation.The discovery of favorite reservoirs with relative high porosity and permeability is important to gas reservoir development.In this paper,we find out that the formation of favorite sandstone reservoirs is controlled by main channel sand,Indo-Chinese Epoch paleogeomorphology and sequence boundaries by means of thin sections observed,sedimentary faces and reservoirs fine analysis.Sandstones formed in main channel zone bear coarse size,high maturity of texture and composition as well as primary pores.The fluctuation of paleogeomorphology underlay Leikoupo Formation caused the formation of high-energy channel in highland and slope of lower T3x2 subsection.The sedimentary sandstones have high porosity and permeability.During process of burying and heating,the mudstones early formed in the lake flooding surface may generate acidic water,which may be helpful for the formation of dissolution porosity.We use the array induction imaging log and nuclear magnetic resonance experiment to calculate the irreducible and movable water,and then divide the reservoirs of T3x2 section into gas layer,gas-water layer and water layer.The gas-bearing condition is controlled by physical property,sedimentary facies and tectonic fluctuation.The movable water saturation has positive relation with physical properties.Gas is mainly accumulated on the highland of channel lapping zone,upper sub-member,and top of lower T3x2.
Upper Triassic Xujiahe calcarenaceous sandstone is widespread and tight in the west Sichuan depression.The high-quality reservoir of calcarenaceous sandstone was firstly touched in the Fenggu structure in 2005.It is change the view that calcarenaceous sandstone can not form reservoir.So far,the controlling factors for the formation of high quality reservoir of calcarenaceous sandstone are unclear.In this paper,we use cast thin-sections,scanning electron microscope,physical analysis,and water-rock interaction to describe the basic characteristics of T3x4 calcarenaceous sandstone in the Fenggu structure.We discuss the potential reasons including sedimentary environment，diagenesis and tectonic movement to control the formation reasons of high-quality reservoir of calcarenaceous sandstone.The results show that the calcarenaceous sandstone is characterized by medium-well sort,low compositional maturity and medium-fine grained.The reservoir space bears dissolved pores between grains and residual intergranular pores,belonging to extra-low porosity and extra-low permeability reservoir.Sedimentary and diagenesis are major factors for the formation of high-quality reservoir of calcarenaceous sandstone.Among them,the favorable sedimentary facies zone and high calcarenaceous content are the preconditions to form high-quality reservoir.The dissolution of organic acids,filling of early hydrocarbons and cementation of early carbonates under the buried process are the keys to form high-quality reservoir.
As an example of Chang 8 member of Yanchang Formation in the Ordos basin,we use the short-term base-level cycle theory of high-resolution sequence stratigraphy to discuss the genesis of the reservoir sandstones of braided delta front in the submarine distributary channel and mouth bar.The various types of sandstones are controlled by base-level change and A/S ratio which is the ratio of tolerable space and sediment supply flux.In the processing of base level rising,if A/S<1,the sandstone is formed in the multi-overlied submarine channel;if A/S>1,the sandstone is deposited in the integrated channel.In the processing of base level falling,if A/S<1,the sandstone is formed in the integrated mouth bar;if A/S>1,the sandstone is formed in the overlied mouth bar.Based on sandstone formation,three types and six subtypes of sandbodies are identified at the braided delta front of Xifeng area,three microfacies areas are obviously divided into submarine distributary channel area,mixed area of submarine distributary channel-mouth bar,and mouth bar area from the shore line to the lake center.
In Maxi area,abnormal overpressure occurs widely in the lower Tertiary Shahejie Formation,including the second and third members of the Shahejie Formation,especially the upper of the third member of Shahejie Formation with pressure coefficient over 1.37.Laterally,the pressure coefficient decreases from central part of sag to the edge.The major cause of the overpressure is related to the hydrocarbon generation.Three functions of overpressure for hydrocarbon pooling in the sag follow as:improve reservoir property,enhance sealing capability,and provide the power for the deep hydrocarbon migration.Thus,the overpressure is important to hydrocarbon migration.We establish the pattern of overpressure-moderate pore-structural petroleum pool in the Rendong slope,the pattern of overpressure-moderate pore-lithological petroleum pool in the central part of Maxi sag,and the pattern of overpressure-moderate and high pore-structural and lithological composite petroleum pool in Nanmazhuang slope.
Based on the newly obtained high resolution 3D seismic data,we analysed the characteristics of strike-slip faults in Cenozoic Qikou sag and its controlling role in basin evolution.There develop two group strike-slip faults with three branches in Cenozoic Qikou sag,the dextral Lankao-Liaocheng strike-slip fault system coastal strike-slip fault zone and Yangerzhuang strike-slip fault zone,and the sinistral Zhangjiakou-Penglai strike-slip fault system Haihe strike-slip fault zone.Characteristics and spatial distribution of Yangerzhuang strike-slip fault zone suggested that the strike-slip fault zone should be the main branch of the dextral Lankao-Liaocheng strike-slip fault system but not the costal branch as another view.One major result of the strike-slip tectonic is the sharp increase in number of extensional faults.The Cenozoic strike-slip tectonic can divided into two episodes of late Shahejie Formation episode and Minghuazhen Formation episode.The strike-slip tectonics originated from the collisions of surrounding plates.The late Shahejie Formation episode movement is corresponding to the opening of South China Sea at about 34Ma,and the Minghuazhen Formation episode movement is corresponding to the Tibet plateau fast uplifting at about Ma.Strike-slip fault zone divided the Qikou sag into three blocks with different structure style.Due to the strike-slip tectonic the evolution of Qikou sag is distinct from classical extensional basin.In the rifting episode,there were several subsidence centers and one main subsidence center,meanwhile the depocenter,the main subsidence center and the fault activity center of different evolution stages migrated toward Northeast.In the thermal subsidence episode,the rate of deposit and subsidence and fault movement sped up,and the intensity center of fault movement migrated toward Northeast.
Huoshiling Formation of Dongling area in Changling depression is a typical residual basin.In recent years,a great breakthrough has been made in the Huoshiling clastic exploration of the Dongling area.In this paper,we make clear the feature of petroleum accumulation and enriching pattern after analyzing accumulation condition of Huoshiling Formation in the Dongling area.In Huoshiling Formation,the dark mudstone with big thickness and wide distribution,which was formed in the semi-deep and deep lake facies exists,is at mature-high mature stage of thermal maturity.There are two types of reservoirs in Huoshiling Formation,one is the delta front sand bodies of K1h1,the other is the volcanic reservoir of K1h2.The K1h1 reservoir is a lithologic and stratigraphic reservoir of self-generation and self-accumulation while the K1h2 reservoir is a structural-lithologic one of lower-generation and upper-accumulation.The distribution of hydrocarbon reservoirs is controlled by K1h1source rocks.The difference of fluid transporting conditions leads to distribution of gas in western part and oil in eastern one.Trap conditions confine the reservoir type and hydrocarbon enrichment.
The combination of source rock,reservoir and cap rock in the Persian Khuff Formation is the most important gas accumulation combination in the Persian Gulf basin.Both Permian Khuff carbonate and interlayer anhydrite consist in the basic elements of gas accumulation combination of Persian Khuff Formation.The Silurian Qusaiba Formation hot shale is the source rock,with wide distribution,high TOCand moderate thermal maturity at late Craterous.The time of trap formation is earlier than that of hydrocarbon generation window,and many basement faults take vertically a good passageway for hydrocarbon migration from Qusaiba hot shale to Unayzah sandstone and the Unayzah sandstone make a lateral migration passageway.The cyclically deposited anhydrite and carbonates act the good cap rock and high quality reservoir.The Khuff Formation reservoir rocks with good original property are composed of oolite,pellete,biodetritus packstone and grainstone,with good moldic pore and interparticle pore.The action of leaching and dolomitization greatly improved the reservoir pore at later stage.In most area,the faults do not make the cap rock loss the sealing,so little gas is lost.The potential area of gas exploration is in the overlay area of Qusaiba Formation mature source rock and interlayer anhydrite,including West Arabian sub-basin,central-east part of Widyan-Mesopotamia sub-basin,northwest of Persian Gulf,and southern area of Ghawar oil field.It is paid more attention in the future to identify the big traps with low closure.Additionally,for the high economy limit of exploration and development in the Middle East,the production for small hydrocarbon reservoirs need the support of high oil price.
Abnormal overpressures exist widely in a certain area and depth in the basins of Qaidam basin and Yinggehai basin.Sedimentary and tectonic evolution,feature and origin of overpressure,and hydrocarbon accumulation history are compared to illustrate the relationship between overpressure system and hydrocarbon accumulation in the process of basin evolution.Results show that two basins accepted the rapid deposition of sediments and formed the thick source rock,which is corresponding to the main layer with overpressure system.Depocenter and tectonism at the deposition stage strictly control the distribution of overpressure,and the top interface of overpressure generally represents a trend of being higher in depocenter,gradually decreasing to basin edge,and even disappearing.Hydrocarbons occur near the interface of overpressure and normal pressure system,and it also has a great potential in an enclosed and well preserved deep area.Overpressures provide the force for driving hydrocarbon migration and control the distribution of reservoir in a certain background.The process of hydrocarbon accumulation can seriously influence the formation and evolution of overpressure system.
The petroleum geology on accretionary wedge was seldom studied as its intensive tectonic deformation and complex geologic setting.Rakhine coast of Myanmar is atypical accretionary wedge,which lies in the conjunction area of the Eurasian Plate and Indian Plate.Petroleum geologic characteristics and accumulation patterns are discussed here in a certain exploration block in Rakhine coast.There is good hydrocarbon generation ability in this area,but the tectonic movements are so intensive that the reservoir became more discontinuous and the former petroleum reservoirs were destroyed.It is concluded that preservation ability is the key factor of hydrocarbon accumulation.Searching for better preservation condition areas is the target for future petroleum exploration.
Based on statistics and integrate analysis of data on carbonate basins in the world,we discuss characteristics of carbonate reservoirs,distribution of petroleum resources in different geologic periods in six regions of enriched oil and gas.High quality reservoirs in Middle East-European region,Central Asia- Russia-North America,Africa,South America,China-Asia Pacific region,and South Asia-Pacific region are distributed in Jurassic-Cretaceous,upper Paleozoic,Cretaceous-Cenozoic,Cretaceous,lower-Paleozoic,and Cenozoic,respectively.Three types of reservoir lithology are limestone,dolomite and chalk,in which limestone and dolomite are dominant.The older age the reservoir is,the larger proportion the dolomite is;but the younger age the reservoir is,the larger proportion the limestone is.Distribution of reservoirs is controlled by deposited facies.The particles beaches,tidal flat and lagoon are profitable to form the dolomite.The deposited facies for high quality reservoir formation is bioconstructed.Distribution of petroleum resources is controlled by carbonate space.Most of petroleum resource is distributed from Carboniferous to Tertiary,the oil is dominated in Cretaceous,the gas is Permian and Cretaceous.Additionally,the abundant petroleum resources are also disturbed in Carboniferous,Jurassic and Paleocene.
Fluid inclusion technique is an effective tool for exploring oil and gas resource in deeply buried carbonate rocks,but its accuracy is dependent on the reliability of fluid inclusion homogenization temperatures.The distribution of homogenization temperature of fluid inclusions in deeply buried carbonate rocks indicates that the initial homogenization temperature pattern has been distorted by the ubiquitous volumetric re-equilibration so that the dominant peak of homogenization temperatures can not be representative of the real original peak value.It is helpful for identifying the extent of fluid inclusion volumetric re-equilibration to reveal their true homogenization temperatures.This method may be important for the fluid inclusion technique application in the deeply buried carbonate rock.It gives a chance to interpret scientifically and reasonably multistage oil-gas migration and accumulation,and constrain accurately the time,temperature and pressure of petroleum accumulation in the deeply buried carbonate rocks.
Although there is abundant of natural gas in tight sand matrix,the gas supply capacity of each layer is different when adopting commingling production in the multi-layer of tight sand gas reservoir.The gas supply capacity of each layer may be impacted by rapid decrease of reservoir pressure and change of water saturation during production.We select the tight sandstone samples from Ordos basin to conduct the experiments so as to test the effect of water saturation on gas supply capacity,and take a contrast of water saturation and effective stress on gas supply capacity of the tight sandstone samples with different permeability.The results show that the effective stress severely impacts the gas supply capacity;with effective stress increase,the gas production for low permeability cores decreases,but the gas production for high permeability cores increase.So the effective stress increase aggravates the difference between gas supply capacities of different permeability rocks.Under in-situ effective stress condition,the gas supply capacity decreases significantly with water saturation increase and permeability decrease.The smaller the permeability is，the more significant the gas supply capacity decreases.The bigger the permeability range of core sample groups is,the more different the contribution rate of gas production is.
Since the finite conductivity vertical fractures in the low permeability reservoirs will be formed after fracture treatment of well, we setup the rate decline mathematical model in consideration with threshold pressure gradient and draw the rate decline type curves of fractured well after calculation.We discuss the tendency of curve change.We also illustrate the influence of threshold pressure gradient on productivity of example well in the low permeability reservoirs.The results show that the production decrease rate for the finite conductivity vertical fractures wells in the threshold pressure gradient reservoir is faster than that of ordinary reservoirs, and this difference is especially significant in the middle or later stage of production.The case indicates that the influence of threshold pressure gradient should not be ignored when rate decline for the finite conductivity vertical fractures well in the low permeability reservoirs.
Horizontal well is one of the most effective ways for the development of tight sand gas reservoirs.The parameters,including effective drainage area,dynamic control reserves,productivity and so on,are directly impacted by horizontal well length.Aimed to the geological feature of the lenticular,isolated distribution of the most effective sand bodies in the Sulige type tight sand gas reservoir,integrating the static and dynamic,geological and development,technical and economic factors,rational horizontal well length is derived from five aspects,geological evaluation,theoretical formula calculation,numerical simulation,economic assessment and field application effects.Then the method of optimizing horizontal well length in tight sand gas reservoir is established.The results indicate that the rational horizontal well length of Sulige gas field is 1 000-1 200m while using type 70 rigs and drilling an effective sand body in the current economic and technical conditions.The successful application of the method in the Sulige gas field provides a reference for the design of horizontal well length in tight gas reservoirs of other fields.
When the acid fracturing production integrated string is used in a deep well with high temperature and high pressure，it is necessary to avoid the small size or large size pipe diameter.The big wellhead working pressure which is produced by big friction resulted from small tubing size will take wellhead safety risk when the pipe diameter is very small;the poor ability of wellbore loading liquid will make the gas well quit flowing earlier than expected while the pipe diameter is very large.Thus,it is required to select the reasonable selection of tubing string.In this paper,we use the experiment design software to optimize four main parameters of tubing string composition,well depth,construction displacement and fracture propagation pressure gradient which affect gas well wellhead working pressure.Then we calculate the wellhead working pressures based on the designed 14 parameter combination，and get the regression equation for wellhead working pressure.Finally we obtain the wellhead working pressure curve for different parameter combinations by using experimental design.It is advantage to intuitively choose tubing string.The average percent difference is 0.24% between model result and the actual value.So,the experimental design is available to calculate the wellhead working pressure resulted from different parameters，to perform sensitivity analysis,and to design tubing string for new well.
Gas hydrate is a crystalline material like ice formed by natural gas and water under high pressure and low temperature.It has great development prospects for the wide distribution,huge amount of resources and high energy density.This paper introduces how to use seismic inversion to forecast the hydrates distribution without well constraint in Shenhu area by analyzing the differences of impedance values and its distribution characteristics.The forecasting results are tested well.Thus the paper will provide a basis for hydrates exploration and exploitation.
Shale gas mainly occurs as the state of absorption and free in shale reservoirs.The amount of shale adsorbed gas is not only a key parameter of shale gas resource evaluation and target area selection,but also an important standard to evaluate the mining value of shale.We do the isothermal adsorption experiment to obtain the curve of shale adsorption and the parameters of Langmuir volume and Langmuir pressure.We discuss the influence of temperature on shale adsorbed gas and use the Langmuir model to calculate the amount of shale adsorbed gas under formation pressure conditions.According to correlation between temperature,pressure,organic carbon,maturity and gas adsorbed amount,we establish a new model to calculate the amount of shale adsorbed gas as considering formation temperature,pressure,organic carbon,thermal maturity.The new model can calculate the amount of shale adsorbed gas at any burial depth;with the burial depth increases,the amount of shale adsorbed gas decreases.We use the data from one shale gas reservoir to establish the correlation between temperature,pressure,TOC,RO,and gas adsorbed amount,the multiple correlation coefficient is more than 0.95.So,the new model has a potential ability to calculate the amount of the unknown shale adsorbed gas;the calculation result is accurate and reliable and can be used to correctly evaluate the resources yield of shale gas.The new model for calculating the amount of shale adsorbed gas will repair the current method which is generally used without considering the amount of shale adsorbed gas under the isothermal adsorption condition.
Fracture development is one of controlling factors for shale gas reservoir,while there is close correlation between fracture and structural characteristics.Based on structural characteristics in the northern Guizhou area,we discuss the fracture features and distribution of lower Cambrian black shale.In the northern Guizhou area,the folds are mainly trough-like,and the faults are formed under cut and joint of fault system in different directions.The main times of fault system with different trending direction are different.Structural fractures are the main fracture types of the black shale and the horizontal fractures and low-angle fractures are dominant.The fracture-developed area is controlled by faults,especially NE- and NNE-striking faults.The fracture-developed areas are mainly lactated in end of the faults,inflection point,junction of different strike faults,and place between faults with similar striking orientation.Meanwhile,the steep part of anticline is also profitable to the fracture formation.
When salt cores from drill-site are used to simulate solution mining process of salt caverns, they are too small to fully represent the whole salt bed.A new preparation method for solution mining model is put forward in the paper.Materials are selected to make up salt rock model include sodium chloride, clay and so on.Mathematical model of solution mining is set up.Experimental parameters are obtained by similarity ratio.An application case of solution mining simulation with artificial salt rock model is given.
Since oil companies of China is trying to go out for petroleum,it is important for establishing the effective method to study the new opportunity dependency,evaluate and execute the feasibility,considering oversea special resources and investment environments. Oversea project need go through three stages of opportunity identification,technical evaluation and putting into execution.Based on itself strength and weakness,the concrete evaluation program will be established according to different opportunity.The conventional evaluation method which separates the geological and economical evaluations goes against the effective evaluation of oversea exploration opportunity.But the integration method of resources and prospects which thinks over the different evaluation factors can be very effective to make a decision.It is required for the systemic economic evaluation and single index sensitivity to decrease the risks at different exploration phase during the oversea exploration opportunity evaluations.
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