Yanchang Formation shale of Ordos Basin contains a certain amount of amorphous SiO2,which has been proved by SEM observation and X-ray diffraction analysis of bulk rock.The three methods proposed by now to calculate the quantity of amorphous SiO2 have their own flaws.The disadvantages of chemical denudation are experimental period and unconvinced accuracy because of dissolving other minerals.Quantitative analysis of amorphous silica by X-ray diffraction possesses high personal error on the integrated intensity of dome-shaped scattering curve in XRD spectrum of amorphous SiO2.The doping method has high deviation and needs to compound standard sample,while some kinds of pure minerals are hard to obtain.On the basis of summarizing previous researches,a new method that combines QEMSCAN and XRD is proposed for the issue of amorphous SiO2 calculation in multiphase system.The new method avoids the flaws in approaches which have been proposed,and calculates the amount of amorphous SiO2 indirectly according to the quantities of quartz and SiO2 measured respectively.
Based on the natural gas reservoir geochemical behaviors,characteristics of fluid inclusions and numerical simulation of hydrocarbon generation pressurization,the gas driving force of migration,migration style and the accumulation process of the Upper Paleozoic have been analyzed in the Longdong area of Ordos Basin,and it also established natural gas accumulation patterns.It has been conformed that the gas of the first member of Shaanxi Formation(P1s1) and the eighth member of Xiashihezi Formation(P2h8) is not only driven by the overpressure-driven surge flow,but also has an obvious diffusion migration characteristic.Moreover,the natural gas of P2h8 is more obvious.The natural gas migration distance,in vertical,mainly arrives to the bottom of P1s1,which phenomenon is caused by the C-P hydrocarbon generation pressurization.The diffusion migration has an important contribution to the gas migration from P1s1 to P2h8.The gas,which is the overpressure-driven by the hydrocarbon generation and diffusion-driven by the gradient of gas molecule concentration,spills into P1s1 reservoir through matrix porosity and fracture.It could directly accumulate and form P1s1 reservoirs under P1s1 direct caprock development,or further vertically migrate into the advantageous parts of P2h8 to accumulate and form gas reservoirs.
Analytical tests were used in this study such as core observation,casting thin section observation,SEM,high pressure Hg injection and X-ray diffractometer.Based on study of lithology characteristics,physical properties and pore structure on Shan32 member of Shanxi Formation in the north of Zizhou Gasfield in the Ordos Basin,the diagenesis was analyzed qualitatively and quantitatively by multi-parameter.Diagenetic evolution sequence,determined diagenetic stage and porosity evolution were restored.The diagenetic facies of reservoir were divided according to the results of diagenesis analysis,physical property and characteristics of capillary pressure curve.The plane distribution characteristics of diagenetic facies were studied.This research shows that Shan32 reservoir of the study area has experienced four stages of diagenesis which respectively are compaction,cementation,metasomatism and dissolution.It is now in the phase B of middle diagenetic stage,with parts of the late diagenetic stage.The diagenetic facies of reservoir are divided into six types.The most favorable facies distribute in central of underwater distributary channel in the southwest of the study area,which are potato-like or island shaped.These areas are the preferred for gas exploration and development of Shan32 Member in the north of Zizhou Gasfield.
By taking consideration of tectonic evolution,the complicate diagenetic processes of the Sinian Dengying Formation dolomite reservoir can be well discussed.Detailed petrographic observation,measurements of homogenization temperature and carbon and oxygen isotopes were carried out.The complicate diagenesis includes subaerial meteoric karst,filling of fibrous prismatic dolomites,crystal grain dolomites,calcites and quartz,entrapment of hydrocarbons,mesogenetic dissolution,and filling of pyrites.The maximal frequency of the homogenization temperatures of the fluid inclusions in the crystal grain dolomites is 190.0-200.0℃ and 220.0-230.0℃.The maximal frequency in the quartz is 150.0-160.0℃.The δ18OVPDB values of the crystal grain dolomites are commonly lower than -10‰,indicating that the dolomites are hydrothermal dolomites.The dissolution and filling processes of the Dengying Formation dolomite reservoirs were generally related to the activities of fluids,which were controlled by tectonic environments.The coupled tectonic-fluid alterations of the dolomite reservoirs include meteoric dissolution during Tongwan tectonic uplifts,dolomite cementation from seawater during the Dengying stage,hydrothermal dissolution and dolomite and quartz cementation during the Early Cambrian and Permian tectonic tension environments,emplacement of hydrocarbon-bearing fluids and related mesogenetic dissolution and filling of pyrites in the Late Silurian,and finally entrapment of gases during Yanshan-Himalaya deep burial stage.
The reservoir lithology of Longwangmiao Formation of Lower Cambrian in Anyue giant gas field mainly includes residual granule dolomite and crystalline dolomite.The major reservoir space is dissolved vug,followed by residual intergranular pore and intercrystalline pore.The types of reservoir belong to fractured-vugs and fractured-pores with the average porosity of 4.24% and thickness about 36m.The vertical and horizontal distribution of the reservoir is controlled by grain shoal facies in inner-ramp and the material basis of which is grain carbonate rock.The constructive factors during the reservoir evolution include:(1)The intergranular pore of grain carbonate rocks lay a foundation of the reservoir space generation;(2)Penecontemporaneous atmospheric water eluviation results in the continuous distribution of large-area massive vugs;(3)Penecontemporaneous dolomitization was favorable for the preservation of earlier porosity;(4)Supergene karstification in Caledonian stage improved the reservoir performance;(5)Fracture cracking and burial dissolution improved the reservoir performance further.The destructive effects of the reservoir suffered are mainly cementation and compaction,and then the filling of hydrothermal minerals and bitumen.After sedimentation and diagenesis comprehensive analysis,the following recognitions are summarized.The necessary condition for the formation of high quality reservoir is grain shoal facies;Penecontemporaneous atmospheric water eluviation is the precondition for the formation of vuggy reservoir;Undergoing penecontemporaneous dolomitization is a prerequisite for the preservation of earlier porosity;Supergene karstification superposition is necessary for the formation of best reservoir.So the main controlling factors of high quality reservoir generation are “Advantage Facies+ Penecontemporaneous Atmospheric Water Eluviation+Penecontemporaneous Dolomitization+ Supergene Karstification”.
The Dengying Formation in the Sichuan Basin is mainly a set of carbonate sediments,in which the high quality reservoir development is generally controlled by karst effects.In the Early Paleozoic,Micangshan area of northern Sichuan was an exposed land which was relatively stable,and it had good correlation with paleo-uplift of central Sichuan in the Tongwan Period.In this paper,through the analysis of carbon and oxygen isotopic characteristics in the key sections and microscopic observation,we systematically compared the unconformity karst features between the 2nd and 4th members of Dengying Formation.The 2nd member reservoir is characterized by grape-like dolomite which develops bedding,interspersed corrosion caves and fractures,while the 4thmember develops sugar-like dolomite intercrystal pores,algae laminae dolomite acicular dissolved pores and breccia pores.Compared with the former,the 4th member of Dengying Formation has more reservoir space types and they are more developed.Furthermore,carbon and oxygen isotopes near the unconformity of the two layers have a tendency to get lighter from bottom to top,and carbon and oxygen isotope value of the 4th member of Dengying Formation is overall lower than that in the second member,as well as more negative in the vertical distribution.Based on the characteristics above,we can summary that compared to the first period of Tongwan Movements,the second period of tectonic uplift is more strong,leading to deeper supergene karst erosion effect in the 4th member of Dengying Formation.As a result,it reflects that the unconformity of Tongwan Movements plays an important role in controlling the development of Dengying Formation reservoir.
Based on the theory of slope break zone,according to the genetic mechanism,three types of slope break belts,namely tectonic slope-break zone,sedimentary slope break belt and erosion slope break belt are identified in Kunbei-Alaer area,Qaidam Basin.Northern Kunlun fracture slope break belt and the Alaer fracture slope break belt belong to structural slope-break zone;Yuejin Ⅱ-Ⅳ,Kunlun slope break belt belongs to sedimentary slope break belt;Tielimuke slope break belt belongs to the erosion of slope break belt.Slope break belt has obvious effect on sedimentary system and development of lithologic trap.The structural slope-break belt controls the formation of low water period nearshore delta and turbidite fan body,and the main lens shape lithologic trap development channel.The depositional slope-break belt mainly controls the low water period braided river delta fan body development,and erosion slope break belt controls the erosion valley lithologic trap filled during low water period.According to the deposit in the study area,reservoir,oil source and migration and accumulation conditions,we carried out lithologic trap prediction and evaluation under the background of slope break belt,summarized its patterns lithologic reservoir development.The comprehensive analysis shows that Yuejin Ⅱ-Ⅳ and Gasi slope-break belts are the favorable lithologic trap blocks.
The Jurassic in the eastern Junggar Basin is not only an important reservoir stratum,but also a main hydrocarbon source layer，so that it has abundant oil and gas resources.The measured section named after its location is called Ganhezi section,which is in the southern of Fukang Sag of eastern Junggar Basin.Ganhezi section consists of the successive Early-Middle Jurassic.By means of observing and describing the Ganhezi section elaborately,and according to the measured data of rock types,sedimentary structure,rock color and grain size probability accumulative curves,the author analyses the sedimentary facies of the Early-Middle Jurassic in detail.The research of sedimentary facies indicates that Badaowan Formation comprises fluvial facies,shallow lacustrine subfacies and delta front subfacies;Sangonghe Formation consists of braided river facies and shallow lacustrine subfacies;Xishanyao Formation comprises braided river facies and fluvial facies.Based on sedimentary characteristics and the variation of sedimentary facies,an evolutionary model with fluvial facies-lacustrine facies-delta facies-lacustrine facies-braided river facies-lacustrine facies-braided river facies-fluvial facies integrated is proposed.Paleocurrent measurements show that the main paleocurrent direction of Badaowan Formation and Sangonghe Formation were SSW-SW,and according to the Walther′s sedimentary facies sequence law,the provenance of Badaowan Formation and Sangonghe Formation were Kelameili Mountain and the region of Boegda Mountain was subaqueous deposit.The paleocurrent direction of Xishanyao Formation was NW-NWW,which indicates that the provenance was in the east and southeast of the study area.The author speculates that the Beisantai and eastern region of Bogeda Mountain had uplifted preliminarily and the tectonic framework of the eastern Junggar Basin had a great change from Middle Jurassic.
Studying on the upper limits of physical properties of tight reservoir is important for the mechanism research of hydrocarbon accumulation and distribution.The critical throat radius was used to discuss the upper limits of physical properties of tight reservoir in the slope belt of the Shuixigou Group of the Turpan-Hami Basin.The computation of critical throat radius needs to determine several key parameters,such as the ratio of the pore radius and throat radius,wetting angle,difference value between oil or gas density and water density.These key parameters can be acquired by constant-rate mercury penetration technique,wettability analysis,PVT and other experiments.The results show as follows.The ratio of the pore radius and throat radius for tight reservoir is about 90,and wetting angle is approximately 20.48°.Upper limits decrease as formation dip increases,and upper limits of tight gas are more stringent than that of tight oil.Critical throat radius of the tight oil and gas reservoirs are 0.552μm and 0.491μm respectively at a strata dip of 15°,and the according upper limits of physical properties in the tight oil reservoirs are 8.43% and 0.378×10-3μm2,while they are 8.39% and 0.358×10-3μm2 in the tight gas reservoirs.
Based on the analysis of chemical components and stable carbon isotopes of the natural gases from the Paleogene Shahejie Formation in the Qiaokou-Baimiao areas of the Dongpu Depression,the origin,maturity and the mixed proportion of the gases are studied,and the following conclusions are obtained.Three types of natural gases have been discovered,coal-derived gas,oil-derived gas and mixed gases.The methane contents in the Qiaokou area are lower than those in the Baimiao area,while the contents of heavy alkane gases in the Qiaokou area are higher.Gases in the Baimiao area were generated by mature to high-mature source rocks,and gases in the Qiaokou area were generated by low mature to mature source rocks.Gases in the wells Qiao 14,Qiao 73 and Qiao 76 are typical oil-derived gas which was sourced from the sapropelic source rocks in the 3rd member of Shahejie Formation.Gases in the wells Bai 3 and Bai 8,close to the Lanliao deep fault,are typical coal-derived gases,and they were sourced from the Carboniferous-Permian coal measures.Mixed gases in the Qiaokou area are dominated by oil-derived gas,while those in the Baimiao area are dominated by coal-derived gas.The Carboniferous-Permian and Paleogene coal measures both contributed to the mixed gases in the study area.
Owing to the few wells and shallow well depth,it is impossible to predict the distribution of sand and shale and sedimentary facies of deep layers in deep water area by few drilling data.Aimed at the Oligocene of D Sag in the deep-water area of northern South China Sea,this study predicted the distribution of sand and shale based on seismic velocity-lithology analysis by using seismic velocity spectrum and drilling data.Further,the Oligocene sedimentary facies of D Sag was predicted based on the comprehensive analysis about seismic facies and its relationship to single well sedimentary facies and sand and shale distribution.The result showed that the L Group is transitional facies and the Y Group is littoral neritic facies.Neritic facies in the central and southern of the sag in the whole Oligocene,and the local coastal plain on the edge of the sag in the Y Group are rich in shale.While the fan delta and littoral facies on the edge of sag in the Y Group and the delta,fan delta and littoral facies in the northern of the sag in the L Group are rich in sand.
Stress field around a re-fractured gas well is the major factor that leads to the reorientation of hydraulic fractures.Considering in-situ stress,non-uniform distribution of net pressure and the thermal effect,a pseudo-three-dimensional model is developed via displacement discontinuity method and heat source function to analyze the changes of thermoelastic stress field around a re-fractured well,which can be used to simulate the fracture propagation.This paper clarifies the thermoelastic stress distribution around the primary fracture and elaborates the major influence factors.It implies that the increment of the minimum horizontal principal stress and its controlled area are both larger than that of maximum horizontal principal stress,resulting in stress-reverse region that emerges around primary fracture surfaces which is beneficial to fracture reorientation while the failure pressure increases at the same time.Furthermore,the simulation results show that only very small stresses can be induced by the cold-water injection and it plays a limited role in fracture re-orientation and propagation,which means that the thermal stresses induced by the cold-water can be ignored in the study of refracturing technology.It is also found that the net pressure is critical for stress redistribution.Therefore,temporary plugging technology applied in the crack tips can not only prevent the secondary fracture propagation along the primary fracture,but also increase the net pressure in the fracture.This paper provides a theoretical foundation for oriented perforating and temporary plugging technology in re-fractured gas well.
To solve the problem of the experience and theory support for vortex tool′s application in gas fields,an experiment was carried out to examine the influence of the tool on flow regime,liquid loading,pressure drop and critical velocity along the wellbore and to acquire the mechanism of the vortex tool by the equipment which was built to stimulate the gas production.Experiments show that the tool can effectively increase 23% lifted liquid with the same gas rate,decrease 18% pressure drop within the wellbore and decrease 20% critical gas rate.According to the mechanism analysis of the tool,a calculating model was quoted to estimate the critical velocity with vortex tool and validated by the experiment.The study provides a technical support for the use of the tool in field and guides production.
The effect of stress on the reservoir permeability and the features of reservoir heterogeneity and formation water saturation were analyzed by means of a huge number of core experiments and test analyses of outcrop section fine coring in the typical low permeability tight sandstone gas reservoirs.With some representative samples,we analyzed the single-phase gas seepage state of low permeability sandstone reservoir,the impact of water saturation on gas permeability and gas water two phase percolation characteristics by conducting systematically single-phase gas seepage experiments,gas percolation experiments under aquiferous condition and seepage tests of gas-water two-phase.On this basis,we studied the impact of various factors such as reservoir permeability,aquiferous conditions,proration and abandoned conditions,longitudinal reservoir permeability differences and the lateral heterogeneity-blocking zone between reservoir sand bodies on the recovery efficiency of low permeability tight sandstone gas reservoir in the process of depletion-drive development by using the physical simulation experimental techniques for gas reservoir development.Then,these five kinds of factors were sorted according to the weight analysis.The results show that reservoir property and reservoir water saturation have the largest effect on the recovery efficiency,whose weight accounted for 0.24 and 0.38,respectively.This study laid a solid foundation for further improving gas reservoir recovery efficiency.
The effect of drawdown pressure on relative permeability is theoretically and experimentally investigated in this paper.A novel predictive model for gas-water relative permeability on the basis of the fractal theory was derived and the corresponding gas flooding tests were conducted.The predictions of relative permeability by the proposed model were validated by comparing with the conducted experiments.Both theoretical and experimental results indicate the significant effect of driving pressure on relative permeability.The predicted and experimental results demonstrate that lower immobile water saturation,wider two-phase region and higher water relative permeability corresponds to the higher drawdown pressure.
Yuanba Gasfield is a large gas field in the marine strata with the largest burial depth in China till now,and the studies on the characteristics of reef flat reservoirs in the marine strata and the main controlling factors of hydrocarbon accumulation have achieved significant progresses.However,there is no consensus on the origin of natural gases reservoired in the Changxing-Feixianguan Formations in Yuanba and adjacent area.The study on geochemical characteristics indicates that,the natural gases reservoired in the Changxing-Feixianguan Formations in the Yuanba Gasfield are mainly composed of alkane gases which are dominated by methane with dryness coefficients generally higher than 0.995,and the CO2 and H2S display an average content of 8.55% and 6.47%,respectively.The δ13C1and δ13C2 values are in the range of -31.2‰--27.9‰ and -29.9‰--25.0‰,respectively,displaying the positive carbon isotopic series.The δ13CCO2 values are generally higher than -8‰,and the δD1 values are in the range of -156‰--107‰.The identification of gas origin and gas-source correlation indicate that,the natural gases reservoired in the Changxing-Feixianguan Formations in the Yuanba Gasfield have been altered by thermalchemical sulfate reduction,and they are mainly composed of oil cracked gases derived from the secondary cracking of oil generated by the sapropelic-prone source rocks in the Permian Longtan Formation.The CO2 in the gas pools are mainly inorganic and were derived from the interaction between acidic fluid and carbonate reservoirs.
The study on distribution of trace elements in natural gas is still in the exploratory stage due to be lack of the relevant detection technology.Professor Wang,et al.have made important progress by introducing the air-extracting method used for geogas survey for the first time and successfully collected the trace elements in natural gas using nitric acid.The paper aims at preliminarily searching the determination method of trace elements in natural gas on the basis of optimization nitric acid collection medium.The following conclusions could be gotten by experiments:The collection effect of nitric acid with low concentration is better than high concentration.And the 15% nitric acid is the best.Compared with field experiment,the detection value of small volume and cycle experiment indoor is closer to the actual value of trace elements in natural gas.It verified some conclusions about trace elements that proposed by previous researchers by comparing the detection results of trace elements in natural gas from different areas.But its mechanism of action are unknown,and precise quantification of trace elements need to be researched further.
Synthesizing samples of hydrate-bearing sediment in laboratories is an effective way to investigate the properties of gas hydrate occurring in nature.However,it is time-consuming and hard to manipulate.Numerical simulations can easily and quantitatively simulate hydrate formation in sediment by controlling any formation conditions.Therefore,in this work the numerical simulation method was introduced to study the formation process and distribution of gas hydrates in lab-scale sediment under the conditions of constant volume and water bath cycling.The results show that the hydrate sample with relatively uniform distribution can be produced in the well-mixed gas-brine system.However,a long reaction time is still required to ensure that gas hydrates have synthesized completely even though the system temperature and pressure tend to be stable.When an interlayer (i.e.,the permeability or the porosity in the intermediate part is different from its up and below parts) occurring in the sediment,both the permeability and the porosity of interlayer have effects on the formation of gas hydrate at the lab scale,but the final saturation distribution of gas hydrates in the medium is almost the same to that in homogeneous sediment.This could be mainly because the hydrate formation rate is rapid at the early stage,and the interlayer affects the mass transfer in the system significantly,as is opposite in the later period because of the slow reaction rate.After maintaining a long reaction time,the results tend to be consistent.
Based on the tectonic and deposition characteristics,regional geophysical survey as well as hydrocarbon exploration of Qiongdongnan Basin,the development and evolution,and distribution features of the suspected mud diapir,the relationship between the suspected mud diapir and natural gas-hydrate are studied.The results show that the suspected mud diapir,the gas chimney and natural gas-hydrate are mainly distributed in the conjunction area between uplifts and sags,as well as the central of sags,what's more,there are overlapping area in geography between suspected mud diapir and natural gas-hydrate.Biogenic gas and sub-biogenic gas derived from organic matter in shallow layer,as well as thermal gas derived from organic matter in deep strata accumulate in the temperature and pressure stable zone through the gas supply and migration and accumulation system which comprised the suspected mud diapir,the gas chimney,or faults and fractures,and natural gas-hydrate come into being,which show that gas supply system that is composed of suspected mud diapir and gas chimney has space-time coupling configuration relationship with accumulation of natural gas-hydrate.It is forecast that there are three accumulation models of natural gas-hydrate,including self-sourced diffusion biogenic gas and sub-biogenic gas accumulate in place by way of “self-generation and self-bearing”,foreign sourced thermal gas accumulate offsite through faults and fractures by way of “lower-generation and upper storage”,foreign sourced thermal gas accumulate in offsite place through mud diapir and gas chimney by way of “lower-generation and upper storage”.
Based on the rock physical method,filling-models of natural gas hydrate was analyzed in the Muli region of Qinghai-Tibet plateau.The primary data contain different kinds of logging data of DK1 and Dk4,in the depth of 143.40-144.20m and 165.80-166.35m,respectively.Firstly,we estimate several physical properties of siltstone of hydrate by Time average equation.Secondly,rock physical models of gas hydrate are established by the method of Elastic modulus model.According to rock physics,we use two assumptions: Model 1,the gas hydrate is taken as a part of the infilling in pore;Model 2,the gas hydrate is taken as a part of the rock matrix.We calculate the velocities of the layer model on the Model 1 and Model 2 respectively to compare the differences.Thirdly,on the basis of the velocities curves by the theoretical calculations and the sampling data in situ,we suggest that the filling-model of the siltstone is in accord with Model 2 in the DK4 of the depth of 165.80-166.35m.
Nitrogen adsorption,mercury intrusion,scanning electron microscope and methane sorption experiments were analyzed for coals,oil shale and shales to study their pore structure characteristics and storage mechanisms.The results are as follows.(1)There are great differences in pore size scale and pore size distribution among coals,oil shale and shales,which are the result of maturity,clay mineral content,and dissolution effect caused by organic fluid;(2)The microscopic pores in low mature kerogen are not developed with few total pores,exhibiting a minor number of micropores and relatively more mesopores as well,while the mature kerogen has much higher specific surface area and pore volume than the low-mature kerogen and is an important contributor to pore space in shales;(3)The methane sorption capacities don′t match the specific surface areas for coals,oil shale and shales,indicating that coal sample with lower specific surface has the highest methane sorption capacity,called “overbalance sorption”,which may be caused by the molecular aggregation way of “molecular filling” or even “solid solution”.The methane sorption capacity of oil shale may contain a certain amount of dissolved gas in bitumen and oil;high to over-mature organic-rich shales have significant higher methane sorption capacity compared to low-mature shales.
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