The organic matter types for Carboniferous source rocks in Junggar basin are humic and mixing of humic and sapropelic.The Carboniferous source rocks in this area have the large thickness and high TOC,and are fallen within the high thermal maturity.Thus,the source rocks are prone to be moderate\|good scope in the source rock classification.The sedimentary environment and tectonic movements greatly constrained the abundance of organic matter and thermal evolution and caused the difference of the quality of Carboniferous source rocks in the vertical and horizontal directions.For example,the Batamayi Formation has the high quality of source rock in vertical direction,in contrast that the Wucaiwan and Beisantai Formations have the high quality of source rock in horizontal areas.
By means of cores description,well log,logging,paleontology,heavy minerals,and seismic facies,we elucidate the material source of Mingyuefeng Formation in the Oujiang sag,and then comprehensively discuss sedimentary facies and its features,based on structural evolution and relative sea level change.At late Paleocene Mingyuefeng Phase,the Oujiang sag experienced the fault switching sag,the source sediments were transported from two sides of sag,the main source was Mingzhe structural belt in the western sag,and the second was Yandang low bump in the eastern.When the large-scale transgression at middle and later Palaeocene caused the relative sea level rising,the Yandang low bump started accept the sediments and reached the biggest sedimentary area.The sedimentary facies of the sag are representative of seashore and shallow sea,with the abundance of sediment supply from the Mingzhe structural belt.Three large\|scale delta sediments were formed at the western slope of sag,where the seashore sediment lie at the margin of sag,and th-shallow sea sediment was located in the centre of sag.The distribution of sedimentary facies is mainly controlled by structure and the of relative sea level change,especially the later.
By macroscopic evaluation to mudstone caprock in the second member of Lingshui Formation in the Qiongdongnan basin,the caprock is composed of shallow marine mudstone with good lateral continuity,large single-layer thickness,low sandy content,and relatively small total thickness.We calculated the displacement pressure between mudstone of the second member of Lingshui Formation and sandstone of the third member of Lingshui Formation based on relationship between sonic travel time and displacement pressure.Based on formula for difference of displacement pressure and sealing ability,the mudstone of the second member of Lingshui Formation can seal the 1 311-1 552m height of gas column in the sandstone of the third member of Lingshui Formation.Selecting parameters (i.e.lithology,sedimentary environment,largest single-layer thickness,total thickness,sand content,displacement pressure difference between reservoir and caprock)
The achievements of exploration and development in recent years indicate that there exists good condition of natural gas accumulation in the PY-LH zone in Zhujiang River Mouth basin as an important zone for gas exploration,including plenty gas source,fine reservoir-sealing assemblage,good trap conditions and composite transport system.The gas accumulation is summed as follows: later accumulation,single type of gas reservoir.Vertically,natural gas mainly accumulates in the low section of Zhujiang Formation.Laterally,natural gas has a banding distribution along the northeast direction.Based on correlation between forming conditions and distribution of gas reservoirs,natural gas in the PY-LH zone is mainly co-controlled by structure ridge,matching condition between traps and reservoir-cap assemblage,sealing and preservation conditions.
In this paper,we simulate oil and natural gas secondary migration process by injecting oil and natural gas into straight glass tube model saturated water and filling glass beads from bottom in top.The results show that there are two migration stages of piston\|type and advantage-type during oil secondary migration process and natural gas secondary migration has the piston and advantages basic migration styles.We discuss the differences of oil and natural gas secondary migration process based on physical and chemical properties of oil,gas and water.The property of oil and gas itself cause the differences of secondary migration process.In the secondary migration process,oil can replace free water in rock pores and adsorbed water on rock surface,forming the stability with pore rock.So,the oil secondary migration phase is obvious.Natural gas secondary migration is much active owing to strong buoyancy difference between natural gas and formation water density.Thus,the natural gas secondary migration is an intermittent migration which is markedly different from oil secondary migration.
Dolomitization of limestone is paid attention since it improves the reservoir ability,and a lot of works have been done.But,it is paid less attention to secondary limestone of dolomites.The secondary limestone of dolomites is one of the important types of diagenesis in carbonate reservoir research and has great effects on reservoir.In this paper,we measure the petrology of secondary limestones and in the 5th Member of Majiagou Formation,Ma5 Member and the digenetic stage its formation.We discuss the genesis of secondary limestone as well as the controlling factor on its formation.The results show that the palaeogeomorphological lowland area is favorable for secondary limestone of dolomites.The fracture system is also one of the controlling factors for secondary limestone of dolomites.The micritic gypsum bearing dolomite at low temperature condition is prone to secondary limestone.This achievement will improve the prediction of carbonate weathering crust reservoirs,and plays a role in oil and gas exploration.
The sedimentary environment of Baibao\|Huachi in Ordos basin is restored based on logging,core description,etc.We use the thin section to elucidate the physical properties of reservoirs and diagenetic facies,and then set up the correlation between sedimentary environment and diagenetic facies.The research results indicate that the shallow water delta front and deep\|water slump sediment gravity flow deposits were developed in study area.The skeleton sand bodies are mainly composed of distributary channel and sandy debris flow deposits.The rock type is feldspathic sandstone and debris-feldspathic sandstone.The physical property of the reservoir is relatively poor，most of the reservoirs have low porous and low permeable.The main pore type is divided into intergranular pore,and intergranular dissolved pore and microfissure.The diagenetic types which influence the physical property of reservoir include compaction，cementation and dissolution.Sand bodies in different sedimentary environments develop different diagenesis.Weak compaction\|chlorite film cementation develops in the distributary channel and feldspar corrosion of deep water sandy debris,in contrast that the chlorite film cementation\|feldspar corrosion does in the belt of transition.Both of them are favorable places for hydrocarbon accumulation.The diagenetic facies belts incorporating with the sedimentary environment is better to predict the development of favorable reservoir and desserts.
The delta\|front zone of Yanchang Formation in the Maling\|Zhenbei area of Ordos basin is one of the important oil reservoir.Two different sedimentary systems in this area are the far source delta sedimentary system along the northeastern source direction and the western braided river delta sedimentary system.The microfacies of sand reservoir in the Chang 8 oil pools in the Malin-Zhenbei area are divided into mouth bars and channels.The channel microfacies can be further categorized into [JP2]three types as follows:(1) subaqueous distributary channels formed in the delta-front margin with normal depositional features;(2) subaqueous deep\|incised channels with both the sandy debris-flow and drag flow features;(3) waterways in fans with the comprehensive characteristics of sandy debris-flow,slump or turbidite.According to origin of reservoir sedimentary facies formation,the Maling-Zhenbei oil pools can be divided into three types:channel-waterways,turbidite fans and mouth bars.The genesis of sandy bodies and stratigraphical reservoirs not only improve the accuracy of reservoir prediction,but help to guide the petroleum exploration.
Fine reservoir prediction is difficult in Chenghai oilfield，which has complex geological conditions，multi sedimentary types，and diverse reservoirs with rapid changes in vertical and horizontal.For the problem of reservoir prediction，a variety of technical means is used to solve the multiple solutions of reservoir research，such as using seismic attribute analysis techniques to delineated the scope of favorable reservoir，spectral imaging technology to improve the horizontal recognition of the reservoir，logging constrained seismic inversion technology to improve the vertical resolution of reservoir，and river edge detection to describe the end of river.Through the integrated application of various technical advantages, we can achieve the identification and tracking of a single sand from the point to the plane then to the body.
Based on core observation,cast thin section,scanning electron microscopy and permeability analysis,we studied reservoir pore structure characteristics of the Xiaganchaigou Formation in northern Qaidam basin and analyzed reservoir development control factors.The results show that,the original intergranular pore is the main type of reservoir space of the Xiaganchaigou Formation,followed by the dissolution pores and small cracks.The reservoirs are comprehensively evaluated of medium porosity,small pore throat radius and medium penetration reservoirs.Sedimentary facies are the main control factors of reservoir performance;the conglomerate rock of braided river bed subphase in this district is the main reservoir rock.Diagenesis are also affected the reservoir performance,in which compaction and cementation decrease the porosity,dissolution increases secondary porosity.
Based on large amounts of data of lithological characters,physical property,pore structure and thin section,we paraphrased controlling factors of the reservoir development in combination with sedimentary elements and diagenesis.The results indicate that Denglouku Formation sandstone belongs to braided delta plain subfacies in Changling gas field,composed of feldspathic lithic sandstone,the reservoir space consists in the intergranular dissolved pores,associated with low porosity and permeability.Rock source is the basis of sand bodies.the physical properties of quartz sandstone are better than that of lithic quartz sandstone and lithic sandstone.Both sedimentary evolution and position of secondary pores control the distributive intervals of effective reservoir.The plane heterogeneity is constrained by sedimentary microfacies and diagenetic facies.Strong compaction and cementation are the dominant factor to create the low permeability reservoirs,in contrast that dissolved secondary pores are in favor of relatively high permeability zones so as to make the low permeability reservoir become better.
Carbon isotopes of Xujiahe Formation gas in the middle part of west Sichuan depression indicate that natural gas is of coal\|type gas origin.Thermal maturity of natural gas in T3x2 and T3x4 Formations is mature and high mature stage,respectively.δ13C1 values in natural gas of Xiaoquan,Xinchang and Hexingchang is more than that of Gaomiaozi and Fenggu,suggesting that natural gas would be migrated from the former places to the.The different times of hydrocarbon generation and expulsion constrain the migration direction of natural gas which sourced from the source rock.So,the same time of hydrocarbon generation and different time of filling history result in the reversal series of carbon isotopes for different number carbon alkanes gases in the T3x2 Formation.
By measuring the stable carbon isotopes of satisfied hydrocarbon,aromatics and single hydrocarbons in crude oil collected from the Wunan oilfield in southwest margin of Qaidam basin,we discuss the geochemical features of the crude oil.The results indicate that the n-alkanes present a bimodal distribution pattern (i.e.,odd-to-even and even\|to\|odd carbon predominance),associated with low ratios of Pr/Ph (<0.5) and C35-Hopane/C34 -Hopane (<1.0),high abundance of tricyclic\|terpanes and gammacerane,and occurrence of hopane (C35).The aromatic hydrocarbons compounds were mainly composed of naphthalene and phenanthrene,and a relatively high amount of triaromatic steroid compounds occurs.These results confirm that the crude oils in the Wunan oilfield were formed in a mild\|salty to salty redution depositional environment,and the parent input matter mainly derived from the lower aquatic organisms.The biomarker parameters of thermal maturity (i.e.hopanes and steranes) suggest a low thermal maturity of the crude oil.Carbon isotope of crude oils (δ13C bulk) was relatively heavy,in contrast that the carbon isotope values of single molecule hydrocarbons (δ13C n-alkanes) remain unchanged with exception of carbon isotope increase in high carbon number,which also support that the source matter of crude oils were derived from aquatic organisms,as well as the sapropelic organic matter.
Hure oilfield is the biggest oil field in the Qaidam basin.In this paper,we comprehensively integrate the geochemical characteristics of saturated hydrocarbon by means of GC-MS analysis.The results show that the crude oil has even\|odd carbon predominance for n\|alkanes,where biogenicdegradation of crude oil in the shallow reservoir caused the absence of part of n-alkane serials.The normal oil has low Pr/Ph ratios,abundance of gammacerane and C35 homohopane,indicating that the crude oil was formed in strongly reducing salt water environment.The ancient salinity of sedimentary environment forN1-N12 crude oils in shallow reservoir is slightly higher than that of E13 crude oils in deep one.The crude oil has the C21-/C22+ ratio of 1.02-1.71,and the high abundance of C27 sterane,confirming they were soured from bacteria and algae.The low ratios of C29 sterane 20S/（20S+20R）and Ts/Tm suggest the low mature oil.The ratio of C29 sterane 20S/（20S+20R）in the deep E13and shallow N1-N12 reservoir is in range of 0.31-0.40 and 0.29-0.36,respectively.This result indicates that the thermal maturity of oil in the deep reservoir is higher than that in the shallow one.
By means of field geological investigation,we speculate the distribution of Carboniferous source rocks.We use the geochemical parameters (i.e.organic matter abundance,kerogen type,thermal maturity) to comprehensive evaluate the hydrocarbon generation potential of source.The Carboniferous source rocks widely developed in most area of Qaidam basin.The maximum thickness of 900m is located in the Oulongbuluke Mountain in the northern margin of basin,the thickness of source rock in the Gerermu-Wutumeiren-Gansen area of the south margin is about 400-500m as zonal shape distribution along the basin margin.The thickness in the northwest and the southeast parts become thin.The Carboniferous source rocks in Qaidam basin are composed of dark mudstone,carbonate rocks and coals.The dark mudstone as III and II kerogen type has an average value of organic carbon content of 1.28;the thermal maturity reach up to mature and high mature.Thus,the dark mudstone belongs to moderate to good source rocks.The carbonate rocks has a low organic carbon content,with average 0.37%,and the organic matter is Ⅱ1-Ⅱ2 type,hydrocarbon generation potential is poor.Coal is the good gas source rocks.So,the Carboniferous source rocks widely exist in the Qaidam basin,associated with the good petroleum exploration prospect.
After two source rocks samples in the Yaomoshan and Dalongkou sections in Junggar basin are subjected to closed system experiment,we get the amounts of hydrocarbon generation and the geochemical parameters and set up a mode of hydrocarbon generation for the kerogenⅠand Ⅱ1 source rocks at different temperature conditions.The intensity of the different gas constitutes generated from the middle Permian source rock in southern Junggar basin is computed by choosing the related geochemical parameters and the thickness of the mudstone.The results indicate that the amount of oil and gas generation from the typeⅠkerogen is more than that of type Ⅱ1 kerogen.The duration of oil generation of the typeⅠkerogen is from 0.6% to 2.0% RO,in contrast that the thermal maturity for the type Ⅱ1 kerogen is in range of 0.7%-1.3%.The type kerogen begins to generate the gas at RO of 1.3%,and the amounts of gas production go up with thermal maturity increase;the type Ⅱ1 kerogen onset the gas generation at RO of 1.0%.Although the time of gas generation is earlier than that of the type Ⅰ kerogen,the gas production in volume is less than that of the type Ⅰ kerogen.In three geological sections,the gas generation intensity in the Dalongkou section is largest,about 167.52×108m3/km2,with the largest intensity of methane and ethane,the Yaomoshan section is second,about 118.88×108m3/km2,and the last is the Hongyanchi section,about 11.46×108m3/km2.So,the gas generation potential in the Southern Junggar basin is great with extensive exploration
Huaqing area,located in central Ordos basin,is one of the main areas of ultra\|low permeability reservoirs to be explored and developed.In this study,we collected the samples of crude oil produced from the Chang 8,9,10 Formations and source rocks in Chang 7,8 in this area and measured the crude oil and extractable organic matter in source rocks.We used the distribution and constitutes of biomarkers of the crude oil and extractable organic matter in source rocks to determine the possible oil source.The results showed that crude oil in the Chang 8,9,10 Formations have the same source of Chang 7 Formation.
Prestack migration has been an effectively method in some areas with complicated structure and dramatic lateral variation in velocity.In comparison with the wave equation pre-stack migration method to post migration method,the pre-stack migration method in seismic imagery processing of fracture-cave in carbonate rock has ability to obtain high resolution and amplitude-preserved migration results,finely portray the fracture-cave,and highly draw a string of beads.The migration results can reflect real structure underground and enhance the success rate of seismic prediction in carbonate karst area.We compare the pre-stack time migration method with the pre-stack depth migration method in theory,applicability and processing seismic section,and find out that the pre-stack depth migration method can obtain the profitable result in some areas with complicated structure and dramatic lateral variation in velocity.Velocity modeling is an important technique in wave equation pre-stack depth migration，so an accurate interval velocity is a key for wave equation pre-stack depth migration.
In past 30 years,the development of amplitude versus offset (AVO) research went up and down.In recent years,the AVO application has been extensively accepted and used rapidly.In the exploration of the heterogeneous reservoir,the AVO is an irreplaceable method,in comparison with others.In this paper,we discuss the influence of lateral small-scale size and velocity variation on the reflectivity coefficient by means of transverse small-scale design,forward simulation calculation,and comparison of theoretical values of Zoeppritz equation.The reflectivity variation depends on the lateral scale size and velocity.We find a rule of reflectivity coefficient with offset distance in the lateral velocity.
Stratal (body) slice technology has been widely used since it is proposed,which is used not only in seismic sedimentology but more often in reservoir prediction.At present,this technology is a common means in the full comprehensive three\|dimensional seismic interpretation,meanwhile it has some new changes during applications.Seismic attributes slice are divided into time slice,horizon slice,stratal slice and stratal body slice in this article.Stratal slice and stratal body slice are distinguished in detail in this paper.Based on analysis of the principles of stratal slice technology and its application conditions,combined with the application in Binhai slope of Dagang oilfield,this paper indicates that we should pay attention to applicable seismic and geological conditions when using this technology,and describes the extraction of isochronous surface and the application skills.These can provide references for the applications of stratal slice technology.
Fracture is a key facter to improve the property and connectivity of carbonate reservoir, how to optimize the prediction technologies of fractures is an important work.We used the integrated seismic fracture detection technology to predict the weathering crust and fracture reservoir in the Tazhong area and contrasted with the predictive results.The results predicted by the technologies are provably identical with the drilling data. More ineffective fractures may be identified by curvature analysis.The fracture directions predicted by coherence technology are consistent with the fault strikes.The paleo\|stress field analytical method is mainly suitable for the prediction of developing trend of faults and fractures.The prestack AVO gradient method has a good effect in the prediction of fracture belts around large faults and brim of karst fracture-cave body.
The Cretaceous Qingshuihe Formation in the eastern slope of Chepaizi area overlap from Shawan sag to high position of the uplift,and the distribution of the northwest-southeast striking faults as a row and belt shape are profitable to the fault-stratigraphic composite trap in this area.The seismic coherence technology is a tool to identify the small faults.The combination of frequency and amplitude attributes has ability to effectively identify the thin sand pinch-out line.the delta front sand body distribution at different stages of sand formation can be identified by the amplitude characteristics of along layer attribute to predict the detailed development of sand area.The combination of structure interpretation and seismic attributes can evaluate the development of the trap reservoir.By the means of seismic attributes analysis above,we point out that five fault-stratigraphic traps existed at the second stage of sand formation,sand body as an important exploration aim is developed within each traps,and the A and C traps are the preferred target for the future exploration.
In this paper,we discuss the genetic correlation between geochemical anomaly and vertical micro\|migration of hydrocarbons from the subsurface oil and gas reservoirs and its geological significance in petroleum geology by means of vertical migration modes and controlling factors,as well as oil and gas accumulation and geochemical anomaly distribution in the Linnan block oil and gas field in the Bohai Bay basin and the Yakela condensate gas field in the Tarim basin.According to geochemical anomaly distribution,Xiakou fault in the Linnan oil and gas accumulation system act as a barrier for lateral migration of oil and gas but a vertical pathway in the study area,indicating that Xiakou fault plays a role of both relative barrier to lateral migration and absolute pathway to vertical migration.Geochemical anomaly has been distributed as a halo shape around the structural high point of Yakela gas field,suggesting that the gas seal would control vertical migration and space distribution of geochemical anomaly.Distribution of the heavier anomaly is consistent with lateral variation of sealing of caprock,indicating that the sealing of caprock to heavier hydrocarbons is more than that to methane.In two cases,we find out that the near-surface geochemical anomaly is related with oil and gas accumulation and vertical oil and gas micro-migration.
Well production reflects the reserve and it is an effective method for recognizing the reserve by analysis of well production.Thus the study on coalbed methane (CBM) production control factors can provide a basis for electoral district,well site design and engineering development of CBM exploration.The south Qinshui basin is one of the hotspots in CBM exploitation,and the CBM commercially exploitation here comes true firstly in China.The CBM productions vary in different areas,with the production of 2000-5000m3/d commonly in the ground vertical wells.Base on the comparison and analysis of the CBM productions and the geological condition of vertical wells,it is considered that the main geological factors of production control are structure,coal thickness,depth,gas content,permeability and hydrogeololgy.These factors influence well production differently,and the potential of well production depends on the effective combination of main factors.
Unconventional oil and gas resources are playing an increasingly important role.Shale gas has become a hot spot and frontier in current research due to huge resources and successful exploitation in the United States.Since shale reservoir is rich in clay mineral,the damages of fluid sensitivity and stress sensitivity are two important damage factors.The coupling action of two damages will greatly decrease the permeability of reservoir and restrict the engineering effect on developing shale gas.Based on fluid sensitivity of clay shale reservoir,we carried out the stress sensitivity,in comparison with difference of stress sensitivity before and after fluid damage.The results show that the stress sensitivity coefficients after fluid damage increase by 30% for the three type reservoirs with medium-strong degree water sensitivity,strong degree alkali sensitivity and medium-strong degree acid sensitivity,indicating the strong stress sensitive degree.The discrete migration of clay mineral particle,hydrate expansion,fluid lubrication cause the decrease of rock strength,make the seepage channel become narrow,and increase the stress sensitivity damage.Therefore,it is a special significance for the protection and economic development of gas shale reservoir to reduce the invasion of incompatible fluid in the well operation.
For study the effects of cooling rate and particle size of medium to the formation of natural gas hydrate, we conduct the formation experiments of methane hydrate in fine and coarse sands.Five cooling rates are applied to the formation processes.The result shows that the cooling rate affects the nucleation time of methane hydrate in coarse sand obviously.The faster the cooling rate, the shorter the nucleation time.Meanwhile, the slower the cooling rate, the higher the methane gas conversion rate.And the cooling rate also affects the formations both in cooling process and constant temperature process.Under a slower cooling rate, the methane gas conversion rate in constant temperature process is relatively small.Different medium has obvious effect to the formation of methane hydrate within it.Relatively, under same conditions, methane hydrate forms easier in coarse sand than in fine sand; and the gas conversion rate in coarse sand is higher than that in fine sand.
Drilled horizontal well is not absolutely horizontal,the well trajectory is undulant as wave shape.When the bending degree of wellbore is big,the conventional calculation formulas for horizontal well production would cause great error.It is necessary to further analyze the deliverability characteristics of horizontal well.In this paper,the horizontal well with curved trajectory is approximately regarded as a continuous structure which composed of a series of slant wells.We add two modifying factors of slanted pseudo-skin coefficient and partial penetrated pseudo-skin factor,and set up the slant well production formula for anisotropic reservoir.The production calculated by the slant well production formula is compared with the Joshi′s horizontal well production formula.We also discuss the effect of curved trajectory on horizontal well production.The results show that the curved trajectory can overcome the low vertical permeability and ensure the high production for horizontal well when the anisotropy is strong.The horizontal well production increases with increase of slant angle of curved section.When the reservoir anisotropy is weak,the curved trajectory will reduce the horizontal well production.
In this paper,the experiments are subjected to simulate the variations of temperature and pressure in the shale sequence during the gas drilling process.We try to get the behavior of water invasion when the water flow out from the shale sequence during the gas drilling process and gas drilling adjusted to water based drilling.A correlation between water invasion distance and time is established to predict the water invasion scope and collapse range.We use this correlation to simulate two cases about water invasion distance and time,and find out that the early water invasion is fast and the late becomes slow gradually.The water invasion speed for the former case is slower than that for the latter one if the correlation between water invasion distance and time for two cases of are contrasted.The time for water invasion in the former case is 350 times than that for the latter in the 5cm water invasion distance.
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