Based on extensive investigation on outcrops in the Permian,Triassic and Jurassic in the areas of Liulin of Shanxi Province,Yan'an and Yanchang of Shaanxi Province and Fukang of Xinjiang Autonomous Region,the sandbody architecture and quantitative parameters of single channel sandbodies of braided river were studied.For the single channel sandbodies,the thickness is commonly 2-5m,and width is commonly 100-300m.The cross section of single channel sandbodies is lenticular,with flat top and convex bottom,or convex top and convex bottom.At the main flow line,the sandbody is thickest.Toward two sides,the thickness gradient is different.For complex channel sandbodies,the thickness is commonly 5-10m,and width is commonly 1000-3000m.The cross section of complex channel sandbodies is planar.The sandbody architecture is divided into stacking-mosaic type,mosaic type and isolated type.Stacking-mosaic type is further divided into three subtypes,and the mosaic type is further divided into two subtypes.The sandbody architecture is controlled by facies belts of braided river and tectonic movement.
blacustrine fan is an important field for oil & gas exploration within source rock.Based on core,logging,and 3D seismic data,formation condition,sedimentary characteristics,seismic responses,and distribution pattern of sublacustrine fan in west slope break zone of Songliao Basin have been studied.The results of paleotopography reconstruction show that slope break zone is well developed in Yingtai area.Furthermore,slope break zone is an important discharging place for gravity flow sediments.Syndepositional fault movement,earthquake activity,and volcanic eruption are major trigger mechanisms for the formation of gravity flow.Sublacustrine fan is mainly composed of sandy debrite,sandy slide and sandy slump,with rare turbidite.Meanwhile,sublacustrine fan has sensitive seismic response characteristics,which is characterized by lenticular external configuration with varied internal amplitude and frequency in seismic profile.Sublacustrine fan is mainly distributed in the rising stage of forth-order base level cycle in vertical and adjacent to fan delta front in plane.On the whole,sublacustrine fan is characterized by excellent hydrocarbon accumulation condition,which can be a favorable target for lithologic reservoir exploration.
The distribution of overpressure is analyzed for Qingshankou Formation from Rangzijing Slope Zone in southern Songliao Basin.The hydrocarbon migration and accumulation models of reservoirs below the source rocks controlled by the overpressure are studied.The results show “three low and one high” that the overpressure zone is characterized by low seismic velocity,low density,low resistivity and high acoustic travel time.The well pressure is a “three-layered” structure vertically.The depth of overpressure strata varies in different secondary structural zone,which suggests the feature of “strata-controlled”.The main range of overpressure is 10 to 14MPa,which is calculated by the equivalent depth method.There exists a positive correlation between the distribution of overpressure and the depth.The coupling of oil source,overpressure and Tfaults make it possible to migrate downward 272 to 510m theoretically,deeper than the Fuyu oil thickness.The match of overpressure and conduit system under the source rocks leads to vertical evolution of 4 migration patterns.There is a positive correlation between the thickness of hydrocarbon shows in the reservoir and the overpressure of the source rocks.The existence of “dominant pressure leakage compartment” results in shorter down-migration distance which is mainly within 100m in fact,and the down-migration distance varies with the change of “dominant pressure leakage compartment” location.Overall,the Ⅱ and Ⅲ sand groups are the preferable layer which is filled with hydrocarbon in Fuyu oil layer.
Based on the 3D seismic profiles,tectonic feature of Jinxian1-1 oil field at Liaozhong Sag was investigated.On this basis,combined with the physical and chemical characteristics of the oil and gas at hydrocarbon reservoirs,the hydrocarbon accumulation process was analyzed and the hydrocarbon accumulation mode was established.There are several results as follows:(1)Liaozhong-1 fault runs through Liaozhong Sag,which forms strike-slip structural transfer zone.The transfer zone has the characteristics of strike-slip duplex on the plane.Manifestations of Liaozhong-1 fault vary in different parts of the district.(2)Traps in the area had already formed before source rocks generated a large number of hydrocarbons.(3)The MemberⅠof Dongying Formation was subjected to uplift and erosion,and then the activity of faults was enhanced and surface water seeped into underground rock stratum,as a result,oil that was migrated into traps at the early stage suffered biological degradation.Owing to composition fractionations of natural gas during the migration,gas dryness coefficient in the east block of the oil field is bigger than that in the west and the dryness coefficient of shallow gas is bigger than that of the deep.
High-resolution sequence stratigraphy provides an important method for reservoir hierarchy correlation.With the application of high-resolution sequence stratigraphic theory and method,the high-resolution sequence stratigraphy framework of the Donghetang Formation in the central Tabei Uplift was established based on the analysis of well logs,core,outcrop and seismic data.As a third-order sequence,the Donghetang Formation consists of a complete eustatic cycle.According to its relatively stable transgressive surface,it can be divided into six 4th order sequences.Wave-dominated deltas and coastal sedimentary systems were recognized within the sequence and their distribution patterns were defined.It can be concluded that the development of depositional systems are controlled by provenance,palaeogeomorphology and sea-level change.
Based on the prediction and determination of the distribution characteristics of thickness,maturity and organic facies of Oligocene source rocks in the east of Central Depression Belt,according to the calculation of the volume,gas generation quantity and intensity of source rocks,source rocks were comprehensively evaluated and the gas-rich sags were optimized.The results show:(1)Generally,Lingshui source rocks are thicker than those of Yacheng,and the percentages of mud in Ya-2 member and Ling-2 member are the most of all.The mud deposition centers evolved from west to east and from sporadic distribution in Yacheng Formation to regional distribution in Lingshui Formation;(2)The thermal evolution of source rocks was early in the west and late in the east, and the modern maturities of different formations are high in the west and low in the east;(3)The quality of Oligocene source rocks is better in general,in which the coal layer is excellent in gas generation capacity,and the gas generation capacity of mud is from moderate to good.The main organic facies in Yacheng Formation are shallow sea and shore,but the main organic facies in Lingshui Formation are inner and outer shallow sea;(4)Baodao Sag,Changchang Sag and Songnan Sag are all gas-rich sags.However,Baodao Sag is the best,follows by the Changchang Sag,and then by the Songnan Sag.
A detailed study of fault combination of morphological,structural styles and characteristics on the zoning of Changchang Sag of Qiongdongnan Basin was carried out based on the regional structural background,structural analysis and basin dynamics theory methods.Three major fault systems were summarized,such as western dextral transtensional strike-slip fault system,eastern extensional fault system,and Early-Middle Miocene shallow and small fault system.It revealed the structural style and the mechanics mechanism of the fault zones.According to this,this study proposed two favorable exploration zones in Changchang Sag with the data of regional sequence stratigraphic,i.e.,transtensional strike-slip negative flower fault belt and extensional reverse drag structure belt.
The geochemical characteristics of nonhydrocarbon in natural gas in western Sichuan Depression were analyzed to investigate the origin,maturity,migration and source of natural gas in the study area.The nonhydrocarbon gases mainly contain CO2,N2 and noble gas.CO2 mainly comes from the dissolution of carbonate mineral,N2 mainly originates during the thermal evolution of organic matter at mature and high mature stages,and noble gas mainly originates during the radiation process of element in crust rock.The evidence of nonhydrocarbon indicates that natural gas is thermogenic gas derived from the crust and is mainly at mature and high mature stages.The results of gas migration by nonhydrocarbon trace method show that N2 is an effective index for natural gas′s vertical migration,however,when CO2 mainly comes from the dissolution of carbonate mineral,CO2may be not able to trace the migration of natural gas effectively.The analysis of noble gas demonstrates that the Upper Triassic natural gas is mixed gas from argillaceous source rocks and coal of Upper Triassic source rock.
Considering the degree of natural fracture closure,a stress field model of natural fracture face with approaching hydraulic fracture is developed via elasticity theory and fracture mechanics.Moreover,this paper clarifies the definition of induced-stress of hydraulic fracture and the way it works.Based on the sensitivity study of influences on natural fracture stability,it is found that the approaching hydraulic fracture can significantly affect the stability,and the factors include the horizontal principal stress ratio,horizontal principal stress contrast,approaching angle,approaching distance,net pressure,degree of natural fracture closure and the length of hydraulic fracture.In this study,it is also found that the approaching angle and approaching distance deviate the position of shear failure center from original,and the role of horizontal principal stress contrast and its ratio,approaching angle and the net pressure are much more critical in stability of natural fracture than other factors.This paper also analyzes the range within which the shear failure occurs.According to the analysis of the stability of natural facture when the hydraulic facture is approaching,the impacts of hydraulic fracture to the stability of natural fracture are expounded in this paper;therefore,it provides a foothold for developing an accurate and systematic theory of network fracturing in future.
Permeability stress sensitivity of formation is of great research value in oil & gas exploration and development.Experiment samples with Φ2.5cm×5cm,which were classified as matrix,natural fracture and artificial fracture,were selected from four types of typical carbonate rocks.The researches on permeability stress sensitivity and rock mechanics were carried out,and the effect of permeability stress sensitivity influenced by physical and mechanical characters of rock was analyzed.Results show that permeability stress sensitivity can be evaluated by stress sensitivity coefficient for the purpose of conducting a contrastive study in different oil blocks,formations and lithology.The stress sensitivity coefficients of carbonatite matrix samples,natural fracture samples and artificial fracture samples were 0.22,0.49 and 0.63,respectively.It shows a trend of steady increase.The correlation between the stress sensitivity of carbonatite and the permeability is poor.It′s hard to precisely reflect the stress sensitivity of natural fracture because the randomness of stress sensitivity of the artificial fracture sample is bigger.Stress sensitivity is closely related to the mechanical properties of rock.The higher value of rock elastic modulus,the weaker the stress sensitivity.It is expected to strengthen the researches on micromechanism and simulation of stress sensitivity.
Reef-shoal carbonate gas reservoir is different from conventional sand gas reservoir and the effective development of this kind of reservoir is facing some problems.Longgang Gas field is a typical reef-shoal carbonate gas reservoir.The geological research and the trial production showed some characteristics,including the huge heterogeneity of reservoir,the extreme complexity of fluid distribution,the crucial influence on gas wells of formation water and the significant discrepancy in different development wells.The effective development of it mainly encountered problems of reservoir heterogeneity evaluation,fluid distribution description,reserves calculation and productivity evaluation.Aiming at these problems and development characteristics,four technical development strategies were proposed.(1)Utilize well-seismic combination technology for fine reservoir description to enlarge the gas reservoir development scale;(2)Use irregular well networks in the process of well pattern to improve the efficiency of gas reservoir development;(3)Strengthen dynamic monitoring and increase the ability of scientific management to improve the management levels of gas reservoir development;(4)Adhere to the development concept of integrated development to reduce the risk of gas reservoir development.The formulation of gas reservoir development technology strategies can provide guidance for the effective development of Longgang gas reservoir.
Waterflood curves of A,B,C and D are effective methods to analyze reservoir performance and predict recoverable reserves in waterflood oilfields.However,each curve of these represents one kind of water cut trend,and their calculation results of recoverable reserves are very different.If recoverable reserves are obtained by averaging the results of four curves,reservoir recognition may be known by mistake.How to choose the suitable waterflood curve becomes the key of forecasting recoverable reserves and analyzing reservoir performance.Through the research,R*-fw curve which reflects composite production performance is present to evaluate the applicability of waterflood curve in this paper and an example is given to illustrate the evaluation process and rationality of this method,and the application of waterflood curves.
Since conglomerate reservoir has strong original heterogeneity,the injection-production contradiction is very serious,waterflow superiority channels exist in some of the strata,and the water injection development is affected seriously.The particle plugging agent with high strength and slow expansion can swell slowly in the process of the injection,and it can go into the deep bed of the layer effectively,then swell as big as possible to plug off the high permeability layers and the crack strips.With this characteristic,it can plug in the deep effectively,so we carried out the integral profile controlling field test and effectiveness analysis in conglomerate reservoir.Results of the six Middle East blocks in Xinjiang province show that particles with high strength and slow expansion improved the serious heterogeneity and water flooding effect of the conglomerate reservoir effectively.Three years after the construction in the experimental block,the accumulative oil increment is 34 226t,and the oil recovery enhanced by 8.38%.
Hancheng mining area has a great number of coal seams and abundant reserves.However,faults are widely developed,the single layer is thin,and the porosity and permeability are low.The drainage time is long,the production fluctuated seriously during the producing process.There is a high ratio of low-to-moderate production wells in Hancheng mining area.It is an urgent subject to improve single well production,which faces the current coalbed methane development in China.The influencing factors that affect low production wells are analyzed according to geological and engineering aspects.Firstly,the production layer is thin and the reserve controlled by single well is limited.Secondly,the physical property is poor and the production is low.Thirdly,the faults communicate with fracturing fractures,and water has channeling between adjacent layers.Fourthly,the cementing quality is poor or even has no well cementation in shallow layers,causing cement channeling outside casing.Fifthly,the fracturing measure does not meet the designed scale,and the effective seepage radius is small and the stable production period is short.Sixthly,the draining and producing system is unreasonable,leading to stress sensitivity of permeability,and the production declines sharply.According to the research results,corresponding adjustment plan and measures are put forward,including optimizing perforated layers to increase production layer thickness;using multiple fracturing technology in the appropriate production stage to improve seepage area;plugging workover for channeling wells;drilling sidetracking horizontal wells after plugging old wells for well channeling along faults;establishing a reasonable draining and producing system to prolong the stable production period through permeability project intervention.The results have achieved good results in practical application and provide reference for the development of the same type of mining area.
Aiming at the problems in the mechanism interpretation on coal adsorption difference and in the description of the adsorption characteristics of super-low rank and super-high rank coals using Langmuir adsorption model,we adopted the means of quantum chemistry ab initio calculation combined with the isothermal adsorption test.It indicates that the mechanism of coal adsorption difference is mainly controlled by the adsorption interaction energy between coal surface macromolecule and gas molecule,the lower of the adsorption energy,the stronger of the adsorption,and the larger of the adsorption amount.We simplified the De Bore adsorption model based on the calculation results of quantum chemistry,and put forward a new adsorption model.It is suitable for describing the whole ranks coal adsorption,and has a wider suitable scope than the Langmuir model.
Niutitang Formation is one of the most potential strata for exploration in the upper Yangtze platform,therefore,we select Nangao section as an example in Danzhai county of Guizhou Province.Through various analytical methods such as field survey,thin section identification,geochemical analysis,X-ray diffraction mineral analysis,porosity measurement,scanning electron microscopy (SEM) observation and isothermal adsorption methods,studies on Niutitang Formation shale gas characteristics including geology,geochemistry,reservoir and adsorbed gas content were performed.Furthermore,the correlation between organic matter and mineral association was discussed,as well as the controlling factors of gas adsorption.For the section in the lower part,it is composed by mudstone deposited in deep-water environment while in the upper part it is silty shale and/or calcareous siltstone deposited in shallow-water shelf environment.Characteristic trace element ratio shows that black shale was formed in the depositional environment of oxygen reduction with obvious characteristics of hot water sedimentation.The black shale is characterized by the occurrence of type-I kerogen.The TOC values range from 0.38% to 15.31%,with an average of 5.2%.RO values range from 1.60% to 4.15%,with an average of 2.8%.The mineral composition of black shale is predominantly clay minerals (e.g.illite and chlorite),quartz,feldspar,barite,and gypsum.Quartz content is relatively high with an average of 53%,and decreases upwards in the section.Quartz content is too high or too low,which are not conducive to the enrichment of organic matter,and only when the quartz content of between 36.4%and 71.9% it has positive correlation with TOC values.Clay content is relatively low and increases upwards with an average of 34%,but it is negatively correlated with TOC values,which is opposed to the quartz′s.There are a few carbonate minerals near the top of the section.The porosity of black shale and siliceous rocks in the lower section ranges from 0.99% to 4.66% with an average of 2.39%,and the density ranges from 1.99 g/cm3 to 2.62 g/cm3 with an average of 2.47 g/cm3 .Four types of pores are present in the shale,such as interparticle pores,intraparticle pores,fracture pores and organic-matter pores.The first two are more common in gas shale.The adsorption isotherm experiments suggest that adsorbed gas in black shale is from 1.71m3/t to 2.62m3 /t with an average of 2.33m3/t,which indicate a strong adsorption capacity.The adsorption ability of Nangao shale and TOCshows positive correlation,however,shale and Tmax show negative correlation.TOC content is also positively correlated with nanopore distribution frequency.This study shows that,TOC content,quartz content,and nanopore distribution play leading roles in influencing the adsorption capacity of gas in the Nangao shale.
During the exploitation of shale gas,it is necessary to conduct reservoir reconstruction for the purpose of economic recovery.Workers in North America and China now adopt the method of combining drilling and completion of horizontal well with massive hydraulic fracturing,which needs enormous amount of water and sand.The interaction of these fluids and reservoir rocks lays the foundation for the success of reservoir reconstruction,whereas the initial water saturation of reservoirs and the understanding of causes of this state are premises of the method.With studies of the marine shale gas reservoirs in southern China,it is found that gas-enriched reservoir often has ultra-low water saturation,which is caused by hydrocarbon generation,consumption and evaporation,etc.Ultra-low water saturation improves adsorption capacity of shale,extends the movable pore throat radius，and increases the gas phase permeability.However,it also accelerates the water-base rates of adsorption and permeation,deteriorates water and hydrocarbon phase trapping problems，and brings more potential damages to aqueous phase trapping of shale gas.Under this circumstance,more attention needs to be paid to the negative effect of ultra-low water saturation and its work damage during the evaluation,reconstruction,and development of shale gas reservoirs.
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