Lithologic Reservoirs

FWI（FullWaveform Inversion） which is based on the framework ofBayes theory is the leading technology of seismic exploration. The basic idea of FWI is widely used for de-noising, deconvolution, seismic data regularization, 1D impedance inversion, AVA elastic parameter inversion, pre-stack migration imaging, velocity analyzing and tomography. Due to the nonlinearity between the observed data and inverse model parameters, there are still a lot of difficulties when FWI is used for field data processing. The essence of FWI was presented under the frame of statistic theory firstly. It was pointed out that Bayes estimation can be implemented with least squares by assuming that the noise satisfies Gaussian distribution. Then the mathematics physics meaning of the mapping from data space to model space is explained. And the nonlinearity of this mapping is decided by the nonlinear relationship between data space and model space, or decided by the complexity of the model parameter and forward operator. At last, the strategy which can push the practical use of FWI was presented after the comparison of the characteristics between land data and marine data. It was believed that:①the velocity inversion should be based on CWI（characteristic waveform inversion）, but not FWI;②the proportion of phase error in error function should be increased legitimately; ③the prior information about data space and model space should be considered more adequately. Only by these ways, FWI can be pushed to its practical use.

Theory and application of the four-step method of seismic reservoir：A case study of igneous rock of fissure eruption in Junggar Basin

WEI Pingsheng， PAN Jianguo， TAN Kaijun， WANG Weifeng， XU Duonian， GAO Bin

2012, Vol.24(6): 10–16 Abstract ( 525 ) PDF (1268 KB) ( 603 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.002

The four-stepmethod of petroleumseismogeology has been widely used in the exploration and development of oil and gas, and achieves good effects. Based on the four-step method of petroleumseismogeology and combined with the characteristics of reservoir study, this paper elaborated the connotation and inner logical relation of the four-step method of seismic reservoir. The result shows that reservoir geological study is the geological basis, seismic petrophysical experiment and technique study are the experimental basis and technique system, reservoir characterization and modeling is the research core, and comprehensive reservoir evaluation and modeling are the results systemof the seismic reservoir. The case study on the seismic reservoir of igneous rock of fissure eruption in Xai 72 well area in Wuxia area confirms the feasibility and effectiveness of the four-step method, the established reservoir characteristic model and 3D reservoir models guide the exploration and development of this area, and provide a good reference for the reservoir characterization andmodeling about igneous reservoir in other areas.

Can not high rate non-Darcy flow take place in low permeability reservoirs?—Reply to Mr Dou Hongen

LI Chuanliang

2012, Vol.24(6): 17–19 Abstract ( 458 ) PDF (682 KB) ( 533 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.003

Whether high rate non-Darcy flowcan take place in lowpermeability reservoirs, the answer isyes if the Reynolds number is high enough. Whether high rate non-Darcy flowis easier to take place in lowpermeability reservoirs or in high permeability reservoirs, the answer is that it is easier to take place in high permeability reservoirs because the smaller pores in lowpermeability reservoirs tend to confine fluids flow. However measurements in lab show the non-Darcy coefficients of lowpermeability cores are higher than those of high permeability cores, which implies that high rate non-Darcy flowis easier to take place in lowpermeability reservoirs than in high permeability reservoirs. This is a false appearance in experiment. The measurements in lab are seldom applied to field analysis, while well test data are the best choice for engineers to research the gas flow in reservoirs. All the deliverability equations of gas wells contain a term of high rate non-Darcy flowregardless of high permeability reservoirs or lowpermeability reservoirs. All the equations have the same form, but the equations coefficients take different values.

Reservoir heterogeneity and influencing factors of Nen 3 member in Xinli area

HU Wangshui，CAO Chun，HE Haiquan，LI Xiangming，LI Songze，LI Zihao

2012, Vol.24(6): 20–26 Abstract ( 529 ) PDF (1108 KB) ( 608 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.004

In view of the problems that reservoir petrologic characteristics, physical properties, heterogeneity and microscopic pore structure characteristics have not been researched clearly, by comprehensive application of the data of core slices, scanning electron microscope, intrusive mercury curve and well logging, this paper studied the macroscopic and microscopic heterogeneities of the reservoir. The result shows that reservoir of Nen 3 member in Xinli area has strong heterogeneity. The influencing factors of heterogeneity were analyzed. It is considered that sedimentary microfacies fundamentally control the formation of reservoir heterogeneity, and a series of changes caused by diagenesis can enhance the reservoir heterogeneity.

Main controlling factors and models of oil and gas accumulation and distribution of E d1 in Nanpu Depression

FU Guang， XIA Yunqing

2012, Vol.24(6): 27–31 Abstract ( 430 ) PDF (1244 KB) ( 572 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.005

In order to study oil and gas accumulation law of Ed1 in Nanpu Depression, the main controlling factors and models of Ed1 in Nanpu Depression were studied by research method of reservoir anatomy and matching relation between hydrocarbon distribution and accumulation conditions. The result shows that oil and gas accumulation and distribution are controlled by following four factors: （1） faults connected with source rocks are main transporting pathways for oil and gas migratingverticallytoEd1; （2） the place where oil and gas migrate through Ed2 mudstone cap rocks, but sealed by Ng Ⅲ volcanic cap rocks is favorable for oil and gas migratingintoEd1; （3） the places where the ratio between sandstone and stratum is more than 20% are favorable for oil and gas migrating laterally into Ed1; （4） positive structures near faults connected with source rocks are favorable place for oil and gas to accumulate. Oil and gas accumulation models of Ed1 are that oil and gas from underlying Es3 or Es1-Ed3 source rocks migrate along faults connected with source rocks intoEd1 in the places where oil and gas migrate through Ed2 mudstone cap rocks but sealed by Ng Ⅲ volcanic cap rocks, oil and gas migrate laterally into strata of Ed1 with the ratio between sandstone and stratum being more than 20%, accumulate in fault block, fault sealing and fault-lithology traps on positive structures near faults connected with source rocks and form oil and gas reservoirs.

Origin of ultra-low permeability reservoirs in Ordos Basin and its significance

LI Shuheng， FANG Guoqing， YANG Jinlong， LIAO Jianbo， FAN Jianming

2012, Vol.24(6): 32–37 Abstract ( 461 ) PDF (955 KB) ( 573 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.006

The resources of ultra-lowpermeability reservoir are abundant，but for the poor reservoir properties and strong heterogeneity, the development is difficult. According to comprehensive research of sedimentary microfacies and diagenetic facies, it is suggested that there are areas with relatively high porosity and high permeability in ultra-low permeability reservoirs. Due to the good clastic sorting, low content of matrix and poor compaction and cementation during the early diagenetic stage, pores can be well preserved. For the active fluid motion, intensive denudation and dissolution in the later diagenetic stage, delta front subsea distributary channel microfacies and braided turbidite channel microfacies are the favorable reservoir facies belt. This cognition is significant for optimizing hydrocarbon enrichment area and promoting economic development of ultra-lowpermeability reservoir.

Study on meter-scale cycles of the Lower Cretaceous Quantou Formation in SK-1 well

GUO Juanjuan，WU Xinsong，PAN Jianguo，WEI Dongtao，FU Jianwei

2012, Vol.24(6): 38–42 Abstract ( 488 ) PDF (999 KB) ( 501 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.007

Based on the data of core and well logging of SK-1 well, this paper carried out the sedimentary microfacies identification, and divided cycle into third-order, fourth-order, fifth-order and meter-scale cycles. According to the cyclic sequence, this paper carried out the Fischer graphic analysis, and established cyclic stratigraphic framework. The absolute age of Quantou Formation in Songliao Basin was obtained by using well logging spectral analysis, and the cycle times were estimated. The result shows that the fifth-order cycle is 112 ka and fourth-order cycle is 379 ka, which is separately corresponding to Milankovitch eccentricity short circle 85～140 ka and Milankovitch eccentricity long circle 350～400 ka. The results coincide with the result of logging. This further illustrates that the forming of cycle sequence formation is controlled by Milankovitch cycle, which provides scientific foundation for the test of influencing factors of climate change in Cretaceous period.

Hydrocarbon enrichment law of Triassic Chang 2 oil reservoir set in Longzuigou area of Xiasiwan Oilfield, Ordos Basin

ZHAO Weiwei， SONG Heping， YANG Yunxiang， LI Delu

2012, Vol.24(6): 43–48 Abstract ( 466 ) PDF (1147 KB) ( 580 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.008

Based on the data of well drilling, well logging, geological log and production test, combined with the core observation and thin section analysis, the hydrocarbon enrichment law and its main controlling factors of Chang 2 oil reservoir set in Xiasiwan Oilfield of Ordos Basin were studied. The result shows that the formation and enrichment of Chang 2 oil reservoir set are controlled by sedimentary facies, high quality reservoirs, nose-shaped uplift, fault, areal cap rock and migration pathway in Xiasiwan Oilfield, among which the nose-shaped uplift is the most favorable place for hydrocarbon enrichment. As migration pathways, fractures have significant effects on the formation and distribution of Chang 2 oil reservoir set. Lithologic reservoir and structural-lithologic reservoir are the main types of the Chang 2 oil reservoir set.

Reservoir characteristics and evaluation of Yan’an Formation and Chang 3 oil reservoir set in Pengyang area, Ordos Basin

YU Lei，CHEN Jianwen，JIN Shaochen，CHEN Zhenbo，GUO Xiaoyan，CHE Fei

2012, Vol.24(6): 49–53 Abstract ( 537 ) PDF (1116 KB) ( 621 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.009

Based on the data of cores and thin sections of Jurassic Yan’an Formation and Chang 3 oil reservoir set in Pengyang area, combining with testing data, this paper studied the rock characteristics, pore throat types and reservoir properties, and analyzed the influencing factors of reservoir development. The result shows that the reservoir rock is mainly of arcose, reservoir space is mainly of primary intergranular pores, and reservoir properties are mainly controlled by sedimentary environment and diagenesis. Finally the reservoir classification evaluation was carried out by using gray relative analysismethod.

Characteristics of glutenite reservoir of Permian Upper Wuerhe Formation in Zhongguai-Wuba area in the northwestern margin of Junggar Basin

LU Xinchuan，SHI Ji’an, GE Bing，ZHANG Shuncun

2012, Vol.24(6): 54–59 Abstract ( 567 ) PDF (939 KB) ( 700 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.010

Based on the data of cores, thin sections, scanning electron microscope and energy spectrum analysis, combined with the principles and methods of sedimentology, this paper studied the glutenite reservoir of Permian Upper Wuerhe Formation in Zhongguai-Wuba area in the northwestern margin of Junggar Basin. The result shows that the glutenite reservoir is mainly developed in multi-alluvial fan facies with “composite fan” sedimentary sequences, which can be further divided into fan-root, fan-bosom and fan-edge subfacies. Glutenite reservoir is mainly consisted of conglomerate, gravel, sandy conglomerate and conglomeratic coarse sandstone, and also contains a few sandstone and fine sandstone. The gravels in conglomerate are mainly tuff and andesite. Reservoir diageneses are mainly compaction, cementation and dissolution, zeolite dissolution is constructive to the reservoir perperties, and diagenetic stage is mainly of late diagenetic stage A. The porosity ranges from 5% to 15%, and the average porosity is 9.4%. The permeability ranges from 0.08 to 80.00 mD, and the average permeability is 3.05 mD. On the whole, it belongs to the better-medium type reservoir.

Application of constant-rate mercury penetration technique to study of pore throat characteristics of tight reservoir: A case study from the Upper Triassic Yanchang Formation in Ordos Basin

LI Weicheng， ZHANG Yanmei， WANG Fang， ZHU Jing， YE Bo

2012, Vol.24(6): 60–65 Abstract ( 573 ) PDF (529 KB) ( 937 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.011

The lower pore and throat radius parameters from conventional mercury penetration technique affect the reservoir evaluation and later development technique policy constituting. Based on constant-rate mercury penetration technique, the microcosmic pore throat characteristics of tight reservoir of Yanchang Formation of Ordos Basin were analyzed, and the alterations of pore throat characteristic parameters were also quantitatively and clearly characterized. The average pore radius of tight reservoir is about 153 μm and has no correlation with the permeability. The average throat radius is about 0.34 μm and there is a great positive correlation between the throat radius and permeability. The average ratio of pore and throat radius is 556, and there is a negative correlation between the ratio and permeability. While mercury enters into the bigger pores controlled by wide throats for little resistance, the influence of throats is unclear. With input mercury gradually increasing and capillary pressure rising, throats gradually control whole mercury saturation. Using advanced technique to change reservoir formation to increase or enlarge throat radius and decrease the ratioofpore and throat radius, in order to increase permeability, so the development of tight oil can have a good result.

Fracture characteristics of the Triassic Yanchang Formation in the midwest of Ordos Basin

LIU Weigang，ZHOU Lifa，GAO Shujing

2012, Vol.24(6): 66–71 Abstract ( 481 ) PDF (1067 KB) ( 584 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.012

The Triassic Yanchang Formation is the main layer for oil and gas exploration in Ordos Basin and it mainly belongs to low porosity and super-low permeability reservoir. The development stages and characteristics of fractures greatly affect the hydrocarbon migration, accumulation and reservoir forming, and also control the later reformation of the reservoir. Based on the fracture data interpreted fromFMI and STARII imaging logging data, combined with drilling core observation, this paper synthetically analyzed the development characteristics of fractures. It was found out that there mainly developed high angle fractures and vertical fractures of the Triassic Yanchang Formation in the midwest ofOrdos Basin, the principal fracture orientation concentrates on near EW, NE, near SN and NW, and the fractures randomly distributed in longitudinal direction in the study area. This paper also analyzed the controlling factors of fracture development, and it is considered that lithology and strata thickness are the dominant factors which influence the development degree of fractures ofYanchangFormation in this area.

High resolution sequence stratigraphic correlation in Hulihai Subsag, Liaohe Oilfield

XU Xiaohong， PAN Wei， GUO Zengqiang， DAI Lifei

2012, Vol.24(6): 72–75 Abstract ( 545 ) PDF (1 KB) ( 874 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.013

Hulihai Subsag is peripheral depression of Liaohe Oilfield, with low degree of exploration. Under the guidance of the theory of high resolution sequences stratigraphy, combined with comprehensive analysis of rock cores, well logs and seismic data, the stratigraphic sequence correlation of Jiufotang Formation and Shahai Formation of Hulihai Subsag was carried out. Jiufotang Formation was divided into two middle-term cyclic sequences and six short-term cyclic sequences, while Shahai Formation was divided into three middle-term cyclic sequences. Based on isochronous stratigraphic correlation method, the well-tie section was correlated, and the isochronous stratigraphic frameworks were established.

Reservoir characteristics of lower Kepingtage Formation in Tabei area

ZHANG Shaohua，PU Renhai，YUN Lu，SUN Naiquan

2012, Vol.24(6): 76–81 Abstract ( 463 ) PDF (983 KB) ( 828 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.014

Tight sandstone industrial reservoir of lower Kepingtage Formation was firstly found in shun 9 well in Shuntuogu ole area, the pore types and reasons of dense become an important aspect to study the new reservoir type. Based on drilling sections, cores, cast thin sections and scanning electronic microscope, the reservoir characteristics of lower Kepingtage Formation were studied. The result shows that the reservoir of lower Kepingtage Formation was formed in tidal flat and tidal delta. The reservoir rock is composed of fine-grained lithic sandstone, and the texture maturity is medium-high. The reservoir properties are poor, with lowporosity and ultra-lowpermeability. The pore types are mainly residual intergranular pores, followed by grain boundary and intragranular dissolved pores, which are mainly formed by the two times dissolution of siliceous minerals. The poor porosity is mainly due to the influences of cementation and strong compaction. The properties in Tuoputai area is better than that in Shuntuoguole area on the plane, which is possibly caused by the absence of crude bituminization and kaolinite transformation by hydrothermal fluid in Permian.

Diagenesis of Sha 3 member and its effects on reservoir in Banqiao Sag

WANG Wei， YUAN Shuqin， LI Yong， ZHAO Yanwei， ZHANG Zili

2012, Vol.24(6): 82–87 Abstract ( 492 ) PDF (986 KB) ( 424 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.015

Bymeans of casting thin sections and part of the ordinary thin sections and combined with scanning electronic microscope, cathodeluminescence and claymineral X-ray diffraction analysis method, the diagenesis, diagenetic sequence of the third member of Shahejie Formation in Banqiao Sag were analyzed. The result shows that diagenesis is mainly of cementation, metasomatism and dissolution. On the basis of the evolution of organic matter and clay minerals, the diagenetic stage ofBanqiao Sag is divided, and Sha 3 member is mainly in middle diagenetic Aand B stage. Dissolution is constructive for reservoir properties. Throughmulti-factor analysis, the comprehensive reservoir evaluation was carried out, which provides foundation for the deep oil and gas exploration.

High resolution sequence stratigraphy of Yanchang Formation in Fuxian area, Ordos Basin

HUANG Long，TIAN Jingchun，WANG Feng

2012, Vol.24(6): 88–93 Abstract ( 623 ) PDF (1 KB) ( 882 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.016

Under the guidance of high resolution sequence stratigraphy theory, based on field crop, cores and well logging data, the Yanchang Formation in Fuxian area can be divided into one super long-term sequence cycle（SLSC）, four long-term sequence cycles（LSC）, 22 middle-term sequence cycles（MSC） and several short-term sequence cycles （SSC）. The short-term sequence cycles can be subdivided into two species and seven subspecies. We analyzed the styles, sedimentary facies and spatial distribution of the different short-term sequence cycles. We chose middle-term sequence interfaces and max flooding surfaces as correlation interfaces in stratigraphic correlation, and established the sequence stratigraphic framework of Yanchang Formation in Fuxian area, which can provide a theoretical basis for recognizing the distribution of sand bodies and source rocks.

Influence of diagenesis on beach reservoirs of Feixianguan Formation in Puguang Gas Field

WU Tingting， WANG Xingzhi， FENG Renwei

2012, Vol.24(6): 94–100 Abstract ( 502 ) PDF (1473 KB) ( 519 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.017

Based on field crop, core and thin section analysis, the influence of diagenesis on the beach reservoirs in Feixianguan Formation, PuguangGas Field was synthetically studied. Bymeans of studying the relationship of reservoir space and diageneses in a variety of diagenetic environments, the diageneses can be divided into destructive diagenesis （cementation） and constructive diagenesis（dolomitization and dissolution）. The primary pores and part of the secondary pores in beach reservoirs disappeared after cementation. While mixing water dolomitization and burial dissolution which play a significant influence on the development of secondary pores in beach reservoirs, can form reservoir spaces such as intragranular pores,intergranular pores and intercrystal pores.

Hydrocarbon enrichment of Upper Triassic Chang 7 oil reservoir set in Maling area, Ordos Basin

LI Wei，WEN Zhigang

2012, Vol.24(6): 101–105 Abstract ( 512 ) PDF (907 KB) ( 743 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.018

The Chang 7 oil reservoir set has great hydrocarbon potential inMaling area, Ordos Basin.With the development of oil and gas exploration, the exploration difficulty is increasingly growing in Chang 7 oil reservoir set. The accumulation mechanism of lithologic reservoir in tight sandstone gradually becomes the main difficulties for exploration arrangement of Chang 7 oil reservoir set of Yanchang Formation in Ordos Basin. Based on study of the characteristics of source rocks, sedimentary facies, reservoir and structure, the characteristics and rules of reservoir distribution were summarized, and the main controlling factors for hydrocarbon accumulation and enrichment were analyzed. The result shows that Chang 7 oil reservoir set is mainly lithologic reservoir, turbidite facies is the main sedimentary type, and the hydrocarbon accumulation and enrichment is mainly controlled by source rocks, sedimentary facies and reservoir.

Application of shear wave velocity fitting technology in Sulige Gas Field

FENG Xinpeng， LI Jinfu， NIE Jianwei， ZHANG Chao， LI Xu

2012, Vol.24(6): 106–109 Abstract ( 440 ) PDF (755 KB) ( 923 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.019

Shear wave velocity is the necessary condition for prestack inversion, so it can directly affect the result of prestack inversion. There are manymeans to get shear wave velocity, of which the applicable conditions deviated a lot. Based on the rock mineral composition of target zone, the elastic modulus, S-wave and P-wae velocity interval and several rock physical models were applied to obtain the S-wave and P-wae velocity. According to the comparison of model fitting results, we optimized the S-wave fitting model suitable for sand shale formation in Sulige Gas Field. The actual application result indicated that this method improved the accuracy of the simulation of shear wave velocity.

Logging identification and evaluation of low resistivity reservoir in fault-block

WANG Bo， ZHAO Jun， WANG Miao， LIU Shuxia， YANG Dong

2012, Vol.24(6): 110–114 Abstract ( 481 ) PDF (614 KB) ( 666 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.020

Lowresistivity oil layer are widely developed in Wangji Oilfield. Due to the lowcontrast ratio of resistivity between oil layer and water layer, the log interpretation is difficult. Based on core test and formation water analysis, this paper analyzed the origin of low resistivity reservoir. The result shows that formation water salinity divergence, pore structure, thin bed development and drillingmud intrusion are the main influencing factors for lowresistivity of reservoir. This paper summarized three kinds of interpretation methods to identify the lowresistivity oil layer, namely oil and water layer identification in cross plot, induction electrolog and lateral logging united method and invading factor method. The actual practice shows that these interpretation methods are suitable for the identification and evaluation of lowresistivity reservoir.

Oil production calculation for rhombic inverted nine-spot areal well pattern of low permeability reservoirs

ZHU Shengju，ZHANG Jiaosheng，AN Xiaoping，HAN Jianrun

2012, Vol.24(6): 115–120 Abstract ( 524 ) PDF (499 KB) ( 580 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.021

Aiming at the problemthat there is no calculation formula about the yield of rhombic inverted nine-spot areal well pattern in lowpermeability reservoirs up to now, based on the water flooding theory of lowpermeability reservoirs, the yield formula for calculating the rhombic inverted nine-spot areal well pattern was deduced by using the basic formula of low rate non-Darcy flow, flow line integral method and element analysis method. The application range is wider than the square inverted nine-spot areal well pattern. The production rate of eight wells of low permeability reservoirs in the BYS block of Ordos Basin was calculated by the method. The result is close to the real yield, with a relative error of only 8%. Adaptability of the rhombic inverted nine-spot areal well pattern in BYS block was evaluated by using the startup coefficient. Aremarkable result has been obtained preliminarily by the optimization and adjustment in BYS block.

Productivity analysis method of water and gas two-phase flow well in low permeability gas reservoirs

SUN Enhui，LI Xiaoping，WANG Weidong

2012, Vol.24(6): 121–124 Abstract ( 504 ) PDF (353 KB) ( 786 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.022

During the well produces in lowpermeability gas reservoir, it appears the gas and water two-phase flowdue to the existence of edge water, bottom water and interlayer water. The reasonable productivity is associated with kinds of development indexes, and it is helpful for the effective development of gas field. Based on the principle of mass conservation, this paper defined pseudopressure function and threshold pressure gradient of two-phase flowof both gas and water, and deduced trinomial productivity equation of gas and water two-phase flowin lowpermeability gas reservoirs in considering threshold pressure gradient and formation damage effects. This paper expounded the method of calculating the trinomial deliverability equation. Through the analysis of actual case, the relation curves of the well that gas and water two-phase flowunder the influence of threshold pressure gradient and the water/gas quality ratio in low-permeability gas reservoirs was obtained. The research shows that with the increase of threshold pressure gradient and water/gas quality ratio, the AOF becomes small. So it provides a theory basis for gas and water two-phase flow well productivity anddynamic analysis of the well in the existence of edge water, bottomwater and interlayer water in low-permeability gas reservoirs.

Determination of minimum miscibility pressure for CO2 flooding by using PR equation of state

YE Anping， GUO Ping， WANG Shaoping， CHENG Zhongzhao， JIAN Rui

2012, Vol.24(6): 125–128 Abstract ( 507 ) PDF (299 KB) ( 877 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2012.06.023

When carbon dioxide comes in contact with oil, the mass transfer phenomena occur. The compositions of two phases become similar, and the interfacial tension disappears, and then gas and oil form miscible. The minimum miscibility pressure（MMP） is an important parameter in CO2 injection process. There are manymethods for the determination ofMMP, and the slimtube test is the most widely used one. However, the experiments are time-consuming, and the empirical formula has great limitations. Thus the PR equation of state ofMMP determined for CO2 flooding is a good choice. The composition of each component could be determined by the PR equation of state when the gas-liquid phase achieves balance. MMP could be calculated by using the miscibility function. The result shows that the MMP determined by PR equation of state is more accurate than that by empirical equations. The iterative precision of the miscibility function has a significant impact on the result.