Since the elevenfifth plan,tight sand gas got vigorous development in China.Its production is only lower than that of the US and Canada.Aiming at the special geological condition of china,geologists have made new progresses in the theory of tight sand gas.With the indepth exploration,the accumulation theory was constantly improved.Through the analysis of early tight gas reservoir theory,anatomy of typical gas reservoir and experiments simulation etc.,it is thought that there are three main accumulation mechanisms,including the largescale tight sandstone type,the anticline structure compact sandstone type and the block tight sandstone type.Their similarities are the tight sands contacting closely with source rocks,the tight sand and the enriched sweet spot.Their differences are shown in the conducting conditions,capping mechanism,migration and accumulation characteristics etc.The characteristics of largescale tight sandstone are near distance seam hole mesh conducting,reservoir and seal double block and large scale gathered.The latter two are with fracture aperture conducting,high quality sealing cover,block or anticline tectonic control play.China's geological resource of tight sandstone gas is 36.54 trillion cubic meters.The study of the theory,exploration and development technology of largescale of tight sandstone gas are more mature,with geological resource of 30.4 trillion cubic meters.It has the basis and potential for accelerating development.Sichuan Xujiahe Formation and Upper Palaeozoic of Ordos Basin are the realistic key exploration zones.Jurassic of Kuqa northern section,Taibei sag of TurpanHami Basin and the south of Junggar Basin are the next favorable exploration zones.
To study oilgas distribution law of the lower generation and upper accumulation source rockreservoircaprock pattern in oilgasbearing basin,based on the study of condition and mechanism of oilgas migration along fault or along sandbodies on both sides with lateral division migration,by comparing the relative size of the displacement pressure in fault filler and sandbodies on both sides,this study discussed a set of judging method of oilgas migration along fault or along sandbodies on both sides with lateral division migration,and applied it to the discrimination of whether oilgas migrates along 7 faults or along 62 sand layers on both sides with lateral diversion migration in Dongying Formation of 5 Nanpu Depression typical blocks.The result indicated that,in 62 sand layers of Dongying Formation,the displacement pressure of 43 sand layers was less than that of fault filler,oilgas migrated into sand layers with lateral diversion migration;the displacement pressure of 19 sand layers was larger than that of fault filler,so oilgas migrated upward along fault,which was coincident with current result of oilgas drilling revealing the distribution of oilgas.It indicates that the method is feasible to be applied in discrimination of whether oilgas migrated upward along faults or along sandbodies on both sides with lateral division migration.
Previous research showed that shelf slope break zone in Qiongdongnan Basin was formed at the end of Miocene,while paleoslope was developed in the northern Basin at the earlymiddle period of the Miocene.Based on the analysis of the relationship of Miocene slope break zone,regional sea level,delta,and gravity flows,sedimentary features and controlling factors of the gravity flows were concluded with drilling and seismic data.The research showed that sedimentary,fault and flexure slope breaks were developed in the northern Basin at the earlymiddle period of the Miocene,and sedimentary break zone had an important effect on the distribution of the gravity flows.When regional sea level falling at 10.5Ma,Ledong Sag and Lingshui Sag developed largescale and sandrich submarine fans,which could be divided into two periods.Lingshui Sag developed early submarine fans,where turbidite channels moved quickly with large number and weak incision.Ledong Sag developed terminal submarine fans,where turbidite channels distributed stably with smaller amount and strong incision,and lobes bodies' morphology appeared flabellate.Turbidite channels and lobes bodies of submarine fans were the favorable sedimentary units.
South Atlantic is one of the world deep water hydrocarbon exploration hotspots and is enriched in deep water resources.Based on oilgas fields data of international commercial databases statistical analysis and formation rules of coastal basins,it can be seen that deep water hydrocarbon of South Atlantic were distributed mainly in six basins in plane.To specify,they mainly located in rich salt basins in the middle section along strike direction,found more on extensional zone along transverse direction,accumulated in carbonate of transitional period and turbidite of drift period vertically.It is effective to utilize conjugate features analogy to explore deep water hydrocarbon in passive margin.Combining basin data and regional geological knowledge,this paper summarizes the following rules of deep water hydrocarbon accumulation in South Atlantic.(1)Deep water hydrocarbon were formed in three tectonic settings,which are extensional and compressional environments in containedhigh plastic body area,and open environment in nonhigh plastic body area.(2)Three sets of effective source rocks are inclusive,they are lacustrine mudstone in rifting period,marine shale in early and middlelate drift period.(3)Two sets of high quality reservoirs were formed,clastic rocks of delta and turbidite in postsalt and carbonate of lagoon facies in presalt.(4)Two types of regional thick cap rocks were owned,salt and marine shale.(5)A variety of genesis trap types were contained,such as structuralstratigraphic trap,structural trap,etc.(6)Deep water hydrocarbon migrated through fault in short distances and accumulated closely to hydrocarbon generation center.(7)Three sets of important deep water plays were formed,including Upper Cretaceous,Lower Cretaceous and Cenozoic.(8)Deep water hydrocarbon was generally accumulated in late period and was mainly formed in structuralstratigraphic and structural reservoir.According to the established different types of deep water hydrocarbon accumulation patterns,deep water hydrocarbon exploration directions with different structural sections were pointed out.It suggested concentration on proximal superimposed deep water fans of Upper Cretaceous in the north section,slope channels and thrust front of Tertiary in the equator section,postsalt turbidite of extensional zone and presalt carbonate of diaperthrust zone in the middle section,as well as slope channels associated with fault block of Upper Cretaceous in the south section.
Hydrocarbon exploration in the Mahu Sag of the northwestern Junggar Basin has recently gained a significant discoverycontinuous oil plays in the Lower Triassic Baikouquan Formation glutenite reservoir with a proven oil reserve of hundreds of millions tons,which is characterized by an extensive hydrocarbon accumulation far from source sequences.This displays significance of fundamental and practical studies.Here,to improve the theory and practice of the accumulation of this discovery,we address the accumulation mechanisms and enrichment rules of the hydrocarbon accumulations.Results show that there are three favorable conditions for the hydrocarbon accumulation in general:Large hydrocarbon resource base,good reservoir and overlying and underlying preservation conditions,and well matched hydrocarbon charge and evolution.The hydrocarbon accumulation has three special characteristics.High quality lacustrine source rocks provide a good resource base.Largescale transverse faults communicating with source and reservoir sequences make the longdistance migration possible.Fandelta sedimentary system provides good conditions for reservoir and continuous hydrocarbon occurrence.The enrichment of hydrocarbon accumulation is controlled by three elements:prodelta sedimentary facies,structural high points and faults.Abnormal reservoir overpressure and fractures have important impacts on hydrocarbon production.The combination of these controls decides the future favorable exploration targets.
Several Carboniferous inheritance structural traps are identified in the Mahu Sag and its periphery in the northwestern Junggar Basin.These traps are adjacent to Mahu and Penyijingxi hydrocarbon source centers,and develop volcanic reservoir and dolomite reservoir whose physical properties are not controlled by depth.Whether the deep layer develops effective reservoirs,or the traps contain light oil or gas,these 2 key problems restricted the exploration of such giant structural virgin land.Using aeromagnetic anomaly,seismic velocity,source rock evolutional history,genesis of natural gas analysis,it shows that Mabei anticline and Dayijing anticline develop weathered volcanic curst reservoir in the Carboniferous,while the reservoirs in Mahu and Manan anticlines may be not good enough.The Mabei and Mahu anticlines contain kerogencracking gas,Manan anticline contains oilcracking gas,and Dayijing anticline has both oil and gas.According to the reservoir condition,phase behavior,burial depth,etc.,Mabei and Dayijing anticlines were suggested as preferred exploration targets and have potential to yield high productive gas and explore giant gas field.
Source rock condition is an important factor in the formation of lowmature gas.The Jurassic source rocks are widely distributed with large thickness in the eastern Junggar Basin.The organic matter type is Ⅲ,and its maturity is less than 1.0%.Geochemical analysis showed that RO(%) changes slightly,basically between 0.5% and 0.8% from 2 200m to 4 500m.The RO(%) variation is small with the increase of the depth of source rocks,indicating that it has not reached the gas generation peak,and this evolutionary stage holds a long geological history of time.To obtain information about the influences of heating time and temperature during the evolution of sedimentary organic matter,with hydrous pyrolysis,twenty experiments were conducted at different temperatures and heating time.The results showed that alkane gas production is low and change little with increasing pyrolysis time (330days) at 330℃ and 350℃.With the increase of simulation temperature (370℃ and 390℃),the alkane gas production reaches the peak at 1421 days,and after that to the day 30 it showed a slow increase or nearly unchanged,relative to the same temperature for 3 days,the gas production increased 23 times,i.e.,RO increased by 0.2%0.3%.The amount of hydrocarbons gas increased significantly.That means,the effect of time on the evolution of lowmature gas may be related to the maturity.
The Kelameili natural gas field is the only gas reservoir that developed in the volcanic reservoir in the Junggar Basin,northwest China.Geochemical characteristics indicate that the natural gas was sourced from type Ⅲ kerogen developed in the Wucaiwan Sag to the east and the Dishuiquan Sag to the west,respectively.The maturity of the natural gas from the Dishuiquan Sag was lower than that from the Wucaiwan Sag.Lateral variation of the composition,maturity,and isotopes of the natural gas indicate that the main pathway system for the natural gas lateral migration is the EWstriking fault that developed in this district.Natural gas from the Dishuiquan Sag migrates eastward and that from the Wucaiwan migrates westward.Mixing happened at well DX18 district and isotope reversal was observed in this district.Research indicates that fissure and fracture due to latestage tectonic faulting have enhanced the capability of the reservoir.The permeability of the reservoir has enhanced 23 orders higher than that of the background,which in turn makes the faults to be the best hydrocarbon migration pathway systems.The above recognized hydrocarbon migration pathway systems indicate that the hydrocarbon exploration should focus on the traps that have been linked by the faults with the source kitchens.
Subvolcanic rocks are widely distributed in the well Dixi 18 area which is the most important reservoir rocks for the Carboniferous volcanic gas reservoirs in Kelameili Gasfield,of which secondary dissolution pores and tectonic fissures are the main reservoir space.Based on the observation and description of cores,this study conducted casting thin section,chemical element analysis,scanning electron microscope and cathode luminescence analysis to examine the controlling factors and the evolution governing laws,space development in the subvolcanic reservoir.This provides a theoretical basis for studies of the formation mechanisms of similar volcanic reservoirs in China.Formation of primary spaces is mainly controlled by magmatic condensation in the magmatic intrusive stage,while formation of secondary pore spaces is controlled by weathering and leaching process in the tectonic stage and deep burial diagenesis.The spatial location of the primary spaces produced in the magmatic intrusive stage is determined by the distribution of volcanic facies.Volcanic facies are the basis for highquality reservoirs.The tectonic stage is the main time when secondary pores are formed and fractures are formed under tectonism,connecting rocks with the atmosphere to form an open system environment.The fracture zone is a favorable reservoir distribution belt,and the structural position of volcanic rocks determines the development of fractures.The system became a closed system during the burial stage,which is the main period when reservoir spaces are redistributed and diagenesis changes the threedimensional spatial distribution of reservoirs.The dissolution of acid fluids and associated fillings leads to reservoir heterogeneity occurring inside the volcanic bodies.
The Gasi Oilfield is a major petroleum province in the Qaidam Basin.The hydrocarbon charge history of the Gasi E13 Oilfield was studied through a detailed reservoir diagenesis and fluid inclusion investigation using optical microscopy,Cathodoluminescence(CL) microscopy,scanning electron microscopy(SEM),XRD,fluid inclusion petrography and microthermometry.The reservoir diagenetic diagenesis comprises the following sequence:an early calcite/Clay cladding→Feldspar dissolution/quartz overgrowth→late calcite/ Feldspar overgrowth→Feldspar overgrowth dissolution/ microcrystalline quartz→dolomitethe→anhydrite chlorite→anhydrite;while the reservoir fluids evolved from alkalic→acidic→alkalic→acidic→ alkalic conditions.The abundance of quartz overgrowth,calcite and illite is negatively correlated with the reservoir quality,whereas chlorite is positively correlated with the reservoir quality.Two episodes of oil charge occurred in the reservoir.The first episode is represented by predominantly yellow fluorescing oil inclusions being contemporaneous with or just prior to the quartz overgrowth.The second episode is represented by blue fluorescing fluid inclusions occurred after the precipitation of dolomite.The two oil charges occurred around 28 Ma and 8 Ma,respectively.The hydrocarbon reservoir model is characterized by an early major accumulation and a late minor charge with multiple concomitant readjustment.
Organicrich shale was widely distributed in the Qingshankou Formation,QijiaGulong Sag,Songliao Basin,which shows enormous potential in unconventional oil/gas exploration.Based on core observation,thin section,wholerock Xray diffraction,argon ion polishingSEM analysis,rock pyrolysis analysis,and organic carbon analysis,reservoir characteristics in shale section of the Qingshankou Formation have been studied.According to the study results,the lithology in the study area was dominated by siltstone and shaley siltstone with low organic matter.The clay mineral content of the shale was 6.1% 39.3%, total organic matter content was 0.74%4.23%,and organic matter maturity(R O)was 0.62% 1.19%, which indicate the shale were at lowmature to mature evolution stage.Major reservoir spaces in the shale section include intergranular pores,intracrystalline pores,organic pores,dissolved pores,and microfractures.The abnormal overpressure in the shale section of the QingshankouFormation was contributed to restrain the compaction and cementation,and promote development of dissolution and natural fractures,which were favorable to form “sweet spot” in shale (tight) oil exploration.
Taking the finegrained sedimentary rocks of the lower Xinhe Formation in Yabulai Basin as a research object,the lithofacies were subdivided using “four componentsthree endmembers” classification scheme with integrated analysis of minerals,structures and organic carbon content by core observation,thin section identification,Xray diffraction and organic carbon test. The results showed that there were nine lithofacies types that could be identified in the finegrained sedimentary rocks of the lower Xinhe Formation,and six of them are mainly developed,which were organiclean massive clayrich siltstone,organiclean laminated siliceous mixed finegrained sedimentary rocks,organiclean massive felsic claystone,organiccontained laminated siliceous mixed finegrained sedimentary rocks,organiccontained laminated felsic claystone and organicrich laminated carbonate mixed finegrained sedimentary rocks. The different lithofacies types and characteristics reflected the differences of sedimentary environment and depositional mechanism. In the prodelta to semideep lacustrine,the waveenhanced sediment gravity flows are widely developed,which formed the superimposed deposition combination of organiclean massive clayrich siltstonelaminated siliceous mixed finegrained sedimentary rocksmassive felsic claystone from bottom to top. In the semideep to deep lacustrine,the water was relatively quiet with a small amount of terrigenous clast input,and the carbonate and clays were more developed,forming organiccontained to rich laminated mixed finegrained sedimentary rocks and claystones.
In recent years,major progress has been made in intraplatform shoals exploration of Sichuan Basin,Tarim Basin and Amu Darya Basin in Tethyan tectonic domain and shows a good exploration prospect.Based on the case study of subsalt intraplatform shoal gas fields of the MiddleUpper Jurassic CallovianOxfordian in the Right Bank Area of Amu Darya Basin,the characteristics of paleogeomorphology are studied and reconstructed through the methods of layer flattening,residual thickness and compensation thickness,especially the controlling effects of sedimentary paleogeomorphology on intraplatform shoal reservoirs and gas reservoirs characteristics are emphatically analyzed.It illustrated that two largescale basement paleo uplifts developed in the study area,and the development of intraplatform shoal reservoirs is obviously controlled by the sedimentary paleogeomorphic differences formed by the hidden basement paleo uplift,while the monolayer thickness of intraplatform shoal is large.Multistage superposed vertically and continuous distributed laterally,and the physical properties of intraplatform shoals reservoirs are better in the high land of basement paleo uplift,where can form largescale superposed intraplatform shoal reservoirs.In contrast,both the monolayer and total thickness are small,and the physical properties of the intraplatform shoal reservoirs are relatively poor in the depressed areas.The scale of intraplatform shoal reservoirs is limited.Meanwhile,paleogeomorpic differences have important influences on gaswater system,productivity and scale of intraplatform shoal gas fields.The vertical connectivity of intraplatform shoal reservoirs is good and the interlayers do not develop in the areas with high sedimentary geomorphology background.The gaswater system is relatively simple and single borehole production is high,while the connectivity of reservoirs is poor and the development degree of interlayers is good in the depressed areas,with complex gaswater systems and low single well production.The high lands of large inherited paleo uplift tend to form largescale superposed intraplatform shoal gas fields.
Previous researches showed that the condensates from the Kaitemilike Oilfield in the western Qaidam Basin were immature oils based on the ratios of C29 sterane isomers (20S/(20S+20R) and ββ/(αα+ββ)<0.25).However,the new analytical results show that the concentrations of steranes and hopanes in these oils are about 0.5μg/mg and 3.5μg/mg,respectively,much less than 5.0μg/mg and 15μg/mg in lowermature oils,but very similar to that in highmature oil from the well Nan 10 in Nanyushan Oilfield.This feature is completely not consistent with their immaturity.Diamondoid hydrocarbons are a kind of thermally stable compounds and mainly identified in mature and highmature geological samples.The results show that the condensates from Kaitemilike Oilfield are rich in diamondoid hydrocarbons including alky l admantanes and diamantanes,and their concentrations are highest in all studied oil samples from different oilfields,indicating of the high maturity.Based on the relationship between methy l adamantane index MAI (>70),methyl diamantane index MDI (>40) and vitrinite reflectance RO,the vitrinite reflectance RO value could be more than 1.3%,corresponding to condensate generation stage,when those condensates were generated from their source rocks.In addition,the condensate samples from Kaitemilike oilfield are distributed in zone of intensive oil cracking in the plot between the concentrations of C29 regular steranes and 3+4methy l diamantane,indicating that they are a kind of crude oils to have been cracked to some extent.Therefore,the immaturity for those condensates from C29 20S/(20S+20R) ratio is not true,and mainly results from soluable bitumen rich in steranes and triterpanes in immature source rocks during migration.It is consistent with the geochemical characteristics of Neogene source rocks in the study area.In this case,diamondoid hydrocarbons with higher thermal stability have a specific significance in determining the maturity and origin of crude oils compared with steranes and triterpanes.In addition,the new recognition for the maturity of those condensates plays a positive role in further petroleum exploration in this study area.
Artificial gas mixing experiment is frequently adopted in quantifying mixed gases at present.The common process of this experiment is summarized via one case study,and two main problems of the experiment have been put forward.A new multivariate data analysis method is set up to quantitatively calculate the mixed proportion of natural gases.The method is proved in another case study.Through this method,the numbers,composition and proportion of end member samples could be calculated and confirmed even without knowing any information of the potential end member samples or adopting the artificial gas mixing experiment.This method is particularly useful to quantify mixed proportion under complicated geological conditions.
Based on fluid mechanics equations and the Galerkin method,a finite element model has been established to simulate fracture mesh seepage field of horizontal wells volume fracturing,and the relationship between fracture mesh conductivity and production has been studied under different fracture mesh scale.Unlike shale gas,fracture mesh scale is not the bigger the better for tight sand stone gas.It should be maintained in a smalltomedium scale (0.1≤FCI≤0.25) and a high conductivity main fracture is also required.From production SRV curve,it is found that there exists a critical SRV value (optimal value),and the production increase is significantly smaller when SRV is beyond the critical value.In practice,together with SRV,the critical SRVconditions to form smalltomedium scale fracture mesh.An analytic relationship among fracturing fluid pump rate,viscosity,rock dynamic fracture toughness,elastic modulus,Poisson’s ratio,stress,natural fracture parameters and fracture net pressure is given by rock fracture kinetics,and then the optimized pump rate to form smalltomedium scale fracture mesh is determined by dynamic extension conditions on the fracture mesh edge.
The irreducible water saturation is the key parameter of oil and gas reservoir evaluation,productivity prediction and the calculation of reserves.The existent experimental standard of the core irreducible water saturation is not suitable for rock samples of tight gas reservoir.A large number of representative tight sandstone samples were selected for semi permeable diaphragm experiment,NMR experiment and mercury injection experiment.After making a comparative study of these three methods,some conclusions were made.If the plate whose pressure threshold value is 1.5MPa is selected to get the capillary pressure curves,the accurate core irreducible water saturation cannot be obtained.The appropriate pressure threshold value needs to reach 3MPa.The best centrifugal force for getting free water of the tight sandstone samples is 1.379MPa instead of 0.690MPa.Combing T2 distribution in 1.379MPa centrifugal force condition and T2 distribution of saturation NMR,the irreducible water saturation of tight rock samples can be effectively determined.The semipermeable plate capillary pressure curves are different with mercury injection capillary pressure curves in the shape of curve.When the capillary pressure is 1.379MPa,mercury intrusion method can get more reliable irreducible water saturation.The above research results have reference significance for the revision of the industry standard of petroleum and natural gas industry in China.
The distribution of gas and water is complex in the Xujiahe Formation of Guang’an Gasfield.The production capacity is different in various blocks of Xu4 and Xu6 Formations.So it has a great meaning to analyze the distribution of gas and water for the efficient development of Guang’an Gasfield.A proper method was proposed to identify the distribution of gas and water.In the first place,the water saturation interpretation model was established by the core analysis.And the mobile water saturation was counted by the irreducible one,which was obtained from NMR and relative permeability curve data.Finally,the identification standards of gas and water layers were built by combining production data.Then gas and water distribution were compared between Xu6 and Xu4 Formations.The result shows that a large area of gas reservoir bearing with water is found in Xu4 Formation,while sweet spots develop in Xu6 Formation.What is more,the main controlling factors are analyzed on account of gas and water layers recognition.It shows that the gas source difference makes the fullness ratio of reservoir in Xu6 and Xu4 Formations different.The reservoir constituent differences control the hydrocarbon distribution in Xu6 and Xu4 Formations.The structure differences provide the diverse differentiation of gas and water in Xu6 and Xu4 Formations.
Test data for binomial deliverability equation of horizontal gas well is difficult to be obtained in the practical operation,which results in the applications of conventional deliverability test and single point method to be restricted.According to the seepage mechanism of horizontal gas well,combined with gas reservoir material balance equation,a new method calculating binomial deliverability equation coefficients of horizontal gas well are proposed.In this method,basic reservoir and gas parameters are used to calculate binomial deliverability equation coefficient A.The binomial deliverability equation coefficient B can be obtained by matching bottom hole flowing pressure,combined with gas reservoir production dynamic data.According to the method,binomial deliverability equation coefficients and absolute open flow of a horizontal gas well in the Huanglongchang Feixianguan gas reservoir of Sichuan Basin is calculated.Compared with calculation results of actual buildup test data,relative error of absolute open flow calculated with this method is only -4.4%,which indicate that the accuracy of calculated absolute open flow is high.Example researches indicate that the method has good application prospect in the gas reservoirs without deliverability test data.
In order to analyze the genesis of quartz in gas shale and its effect on the reservoir quality,shales of the WufengLongmaxi Formations in the southeastern part of Sichuan Basin are taken as a research object.Based on Xdiffraction analysis,scanning electron microscope combined with cathode luminescence (CL),energy spectrum analysis and major elements test,detrital quartz and diagenetic quartz were identified.Monochromatic CL of diagenetic quartz with less intensity,typically displayed characteristic CLpeak close to wavelengths of about 620nm.Biogenic silica occurs as irregular shape with relatively large aggregates of crypto or microcrystalline.The microsized quartz crystals sourced from the smectite to illite reaction occur as discrete grains,small clusters,thin sheet or micro sheet within the clay matrix.TOC and quartz content have positive correlation,which indicated high quartz content shales enriched in biogenic silica were beneficial to the enrichment of organic matter and reservoir fracturing with a high brittleness.
Based on the well and 3D seismic data in BD area of eastern Ordos Basin,combined with the geology theory and method of sedimentology and sequence stratigraphy,the basic geological conditions and sedimentary controls of coalbed methane（CBM） accumulation were analyzed,and the prediction for favorable area of CBM was made based on the geophysical technique.The research results indicate that BD CBM block has good geological conditions with simple structure,moderate burial depth,good physical reservoir,weak destruction,strong save ability,high gas content and high groundwater salinity.The Sedimentary control function of CBM enrichment was discussed on the basis of the sequence stratigraphy division.It can be concluded from the research that the distribution of coal seam is controlled by sequence stratigraphic framework,the characteristic of coal reservoir is controlled by coaldepositional environment,the surrounding rock of CBM reservoir is controlled by sedimentary system.Based on the analysis of sedimentary controlling factor,we predict for CBM rich region in BD south 3 dimensional area through multisource information fusion methods.Verified by subsequent drilling,the wells in this place have good effects,which is currently the highest gas production part in BD block.The multisource information fusion methods provide reference for foreasting in similar coalbed methane favorable areas,because the scope of prediction and actual drilling results are closely.
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