Table of Content

28 December 2010, Volume 31 Issue 6

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Significant advancem ent in natural gas exploration and developm ent in China during the past sixty years

2010, 31(6):  689-698.  doi:10.11743/ogg20100601

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:Based on analyzing the reserve and production growth of natural gas in China from1949to2009，we summarize theoretical and practical significances of the coal-derived gas theory and sum up the achievements in exploration and development of giant gas fields and their significances.Over the past sixty years，significant advancement has been made in gas exploration and production in China.First，China has become one of the world’s top players in natural gas reserves.In1949，China’s proved geological reserves was only0.385BCM，but in2009，this number exceeded7000BCM.Second，with a annual production of85.2BCM in2009，China is theworld’s7th biggestgas producer now，while itonly produced11.17MCM ofgas in1949.Third，the theory on coalˉderived gas has promoted the rapid advancement of gas exploration and production.In1979，the theory on coal-derived gas emerged as a new theory to lead the exploration and production of natural gas.Fourth，it is an importantway to rapidly developmentChina’s natural gas industry by exploring and developing giantgas fields.By2009，44large and giant gas fields have been discovered in China.They account for80.5%of the total reserves and66.4%of total gas production in China.Significantprogress has beenmade in natural gas exploration and development in China during the past sixty years.

Great hydrocarbon potential in the Paleozoic m arine sequences in China

2010, 31(6):  699-706,752.  doi:10.11743/ogg20100602

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In1984，China made a breakthrough in petroleum exploration in the Paleozoic marine sequenceswith the discovery of the Shacan-2well in Tarim Basin.Since then China has not only leftbehind thewrong idea that there is no hydrocarbon in the Paleozoic marine sequences in China，but also found tens of oil and gas fields in Tarim Basin，Sichuan Basin，Ordos Basin and JunggarBasin.Theories on hydrocarbon generation and accumulation in the Paleozoic marine sequences in China have been brought forward and corresponding exploration techniques have been developed.According to the study of resource potential in the Paleozoic in China，the Paleozoic source rocks，which have not experienced metamorphism，occur in NortheastChina，southern North China，Qaidam Basin，the Hexi corridor and the Qinghai-Tibet area，further proving the great hydrocarbon potential in the Paleozoic marine sequences in China.

Gas accumulation patterns and key exploration techniques of deep gas reservoirs in tight sandstone:an example from gas exploration in the Xujiahe Form ation of the western Sichuan Depression，the Sichuan Basin CaiXiyuan

2010, 31(6):  707-714.  doi:10.11743/ogg20100603

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Deep tight gas reservoirs are characterized by deep burial depth，poor reservoir quality and low production rate，but large exploration potentials.Distribution of favorable source rocks controls the planar distribution of gas reservoirs，and“effective reservoirs”in deep tight sands are the key to gas accumulation and production.Their development is under the control of structure，sedimentary facies and diagenetic facies.Effective porosity controls gas distribution，while fracture controls gas production rate.The gas reservoirs in the Xujiahe Formation in thewestern Sichuan depression feature in ultra-deep，superpressure and extra-tight，challenging prediction of reservoirs and sweetpoints.The3D-3C seism ic exploration technology is capable of solving such problems as quality reservoir prediction，fracture detection and gas potential identification.Ithas been successfully applied to exploration of the deep tight gas reservoirs in the western Sichuan depression.The success rate of exploratory drilling in the secondmember of the Xujiahe Formation is raised from15%to89%，and high yield well ratio increases from9% to 67%，and the discovered gas in place is121.1BCM.H igh efficiency exploration of tight sand gas is realized in the western Sichuan depression.

Distribution of gypsum-salt cap rocks and near-term hydrocarbon exploration targets in the m arine sequences of China

2010, 31(6):  715-724.  doi:10.11743/ogg20100604

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Through reverse thinking，we summarize the status of research in the field of subsalt hydrocarbon exploration，analyze the distribution characteristics for gypsumˉsalt cap rocks，and discuss the potentiality and targets of subsalthydrocarbon explorationwithinmarine seuences in china.Gypsum and salt are excellent cap rocks whichwidely occur in themarine sequences ofTarim and Sichuan basins.Subsalt reservoirs are large in resource volume and are the main targets of future exploration.In southern China，gypsum-salt cap rocksmainly occur in the Lower-Middle Cambrian and Lower-Middle Triassic，in addition to the Cretaceous and Paleogene.The gypsum-salt cap rocks are extensive in lateral distribution but large in differences in different areas.For example，the Lower-Middle Triassic gypsum-salt cap rocks are closely related to hydrocarbon distribution in Sichuan Basin.The Cambrian and Lower-Middle Triassic gypsum-salt cap rocks are relatively thick and are the best seals for the marine reservoirs.The Carboniferous gypsum-salt cap rocks also occur in centralHunan province.Moreover，several gypsum-salt cap rocks also exist in Tarim Basin.For the Tarim platform-basin area，there are two sets of major cap rocks，i.e.the Cambrian and the m iddle-upper Carboniferous gypsum-salt cap rocks，especially the former is the major regional seal.The Cambrian gypsum-salt cap rocks in Bachu-Maigaiti area are large in both areal distribution and continuous thickness.Taking the overall geologic conditions for hydrocarbon accumulation in subsalt area into account，especially the controlling factors of slope and hinge zone for hydrocarbon accumulaˉtion，the paper suggest five plays or fields as themajor targets of near-term exploration in southern China and Tarim Basin.

Geologic and m etallogenic or poolˉform ing effects of the therm odynam ic process and their identification Liu Chiyang

2010, 31(6):  725-733.  doi:10.11743/ogg20100605

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This papermainly discusses the geological effects of thermodynam ic process on the formation of sedimentary basins，structural changes and hydrocarbon occurrence.Thermodynam ic process is an important dynamo type of basin-forming.It is one of the necessary conditions for the formation of a hydrocarbon kitchen，which in the world generally have high or relatively high geothermal backgrounds.Thermodynam ic structures are extensive in distribution，special in structural types，and complex in structural features.Identification methods of the geoˉlogical effects of thermodynam ic process are also discussed.

The Late Paleozoic tectonic evolution and later transform ation in Northeast China

2010, 31(6):  734-742.  doi:10.11743/ogg20100606

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Based on tectonic evolution of deep major faults，stratigraphy and distribution and evolution of lithofacies paleogeography，we redivide major tectonic units in the Late Paleozoic in Northeast China.Late Paleozoic strata in NortheastChina experienced three major tectonic movements，including the Late Hercynian，the Indo-Chinese and the Yanshanian movements.Among them，the Late Hercynian movement is the strongest and the tectonic styles are closed folds and associated thrust faults.The Permo-Carboniferous in NortheastChina mainly experienced twomajor transformation stages.One is from the end ofLate Perm ian orEarlyTriassic to Late Jurassic with the dom inance of compression，folding and corrosion.The other one is from the Early Cretaceous to Late Cretaceouswith the dom inance of extensional rifting.Areaswith overlappingMesozoic basins have well-preserved Permo-Carboniferous，and thus are favorable gas plays in the Paleozoic

Controlling factors and genetic pattern of the O rdovician reservoirs in the Tahe area，Tarim Basin

2010, 31(6):  743-752.  doi:10.11743/ogg20100607

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TheMiddle=LowerOrdovician in the northern Tarim Basin experienced two phases of karstification in theMiddle Caledonian and in the EarlyHercynian，respectively.The karstification mainly took place under low temperature meteoric water conditions at surface or near the surface，and was controlled by five factors;that is，structures（prototype basins and tectonic transformation），sequences（configuration and patterns），lithofacies（sedimentary facies and diagenetic facies），source of fluids（surface，formation and deep fluids）and time.This resulted in fracturedˉvuggy karst reservoirs of various typeswith strong heterogeneity and significant zonation.In the north zone，reservoir spaces are dom inated by big caves and fractures;in the m iddle zone，reservoir spaces are pores，vuggs and fractures;in the south zone，reservoir spaces are mainly fractures with local vuggs and pores.The major controlling factors vary in different areas and different layers.Multistage karstification cycles occurred during the long time and multistage exposure in the north ofTahe area.The development of reservoirs is controlled by single-factor but multistage effectswhich are dom inated by surface karstification，and three sets of cavern-type reservoirs are formed.In the south where the Upper Ordovician is relatively thick，because of short-time exposure and relatively weak karstification，the development of favorable reservoirs are jointly controlled by peleotopography，exposure time，high-energy facie zones，distribution of fractures and faults as well as later burial and dissolution.

Main controlling factors for hydrocarbon accumulation and potential exploration targets in clastic sequences in western-central China

2010, 31(6):  753-762.  doi:10.11743/ogg20100608

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Clastic oil pools in western-central China may be classified into three main types in accordance with their oil/gas origins，namely the internal-sourced（hydrocarbons being sourced inside the clastic sequences，the external-sourced（hydrocarbons being sourced outside the clastic sequences）and them ixed type（hydrocarbons being sourced both inside and outside the clastic sequences）.The interna-sourced pools can be subdivided into selfˉsourced（with source rocks occurringwithin the reservoir interval）and nonself-sourced（with source rocks occurring outside the reservoir intervals），while the external-sourced types can be subdivided into secondary and primary pools.The self-sourced pools in the internal-sourced category feature in both vertical and lateral adjacency of source rocks to reservoirs，which is favorable for the formation of large lithological reservoirs or highly productive structural reservoirs.The major controlling factors for hydrocarbon accumulation in this type of pools are quality hydrocarbon kitchens，upliftswithin a depression and favorable facies zones.They are the primary targets for discovering medium to large reservoirs.The formation of nonself-sourced reservoirs requires not only the existence of source rocks within the clastic sequences，but also the vertical/lateral carrier systems for hydrocarbon m igration into the upper clastic reservoirs.Theirmain controlling factors include quality hydrocarbon kitchens，carrier systems and palaeo-structures/structures.They are potential exploration targets for discovering highly productive structural reservoirs.The formation of external-sourced pools require both vertical adjacency to underlying quality kitchens or lateral adjacency to large marine reservoirs（fields）and m igration networks consisting of faults，unconform ities or carrier beds.Theirmain controlling factors are efficiency of carrier systems and scales of underlying oil/gas reservoirs.They are important targets for discoverings mall to medium secondary oil/gas reservoir clusters and larger stratigraphic reservoirs.

Characteristics of the complex O rdovician carbonate reservoirs in the Tarim Basin

2010, 31(6):  763-769.  doi:10.11743/ogg20100609

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Multidisciplinary analyses of reservoir geology and exploitation geology reveal that the Ordovician carbonate reservoirs in Tarim Basin are differentwith conventional reservoirs.They feature in extensiveness of oil/gas distribution，diversity of oil/gas property，layering and heterogeneity ofhydrocarbon accumulation，and instability of oil/gas production.There are two basic geological conditions controlling the formation of these special reservoirs，namely great reservoirheterogeneity andmultiˉphase hydrocarbon accumulation and latemodification.The special carbonate reservoirs thathave large oil/gas-bearing area，complex oil/gas-water contacts and a small amount ofwellswith high and stable production contributing to bulk of the oil/gas production are common in the Ordovician carbonates in Tarim Basin.Therefore，an integrated exploration and development strategy should be employed.

Oil accumulation process in the low-perm eability Chang-8¹ member of Longdong area，the Ordos Basin

2010, 31(6):  770-778,837.  doi:10.11743/ogg20100610

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Oil reservoirs in the Chang-8¹ member of the Yanchang Formation of the Longdong area in Erdos Basin are typical low-permeability reservoirs.An observation of their diagenesis and bitumen occurrence and an analysis of the paleo-fluid indicate a multistage diagenesiswith at least three times ofoil charge in the reservoirs of the member.The previous study results were employed in the analysis of the reservoir features.Based on an analysis of dynam ic conditions，a reliable oil accumulation pattern is proposed.During the late Jurassic when the reservoirs still had favorable porosity and permeability，hydrocarbons generated by the quality source rocks of the Chang-7 ³ member entered the carrier system of the Chang-8 ³ member.The hydrocarbonsm igrated laterally due to buoyancy and accumulated for the first time.Later，with the tilting of the basin，the accumulated oil and gas escaped.At the same time，the continuous compaction and cementation lowered the permeability of the reservoirs.Since the early Cretaceous，the hydrocarbons mainly m igrate and accumulate laterally along the residual pathways that are oil-wet due to long-term contactwith oil.

The Paleozoic prototype basins and their tectonic deform ation in North China and their controlling effects upon hydrocarbon accumulation

2010, 31(6):  779-794.  doi:10.11743/ogg20100611

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Keeping in m ind the principle summarized as“prototype basin controls the source，tectonic deformation controls the pooling”，the article mainly discusses the tectonic evolution of the Paleozoic from prototype basin to deformation aswell as its controlling effectupon the distribution of the Paleozoic source rocks and the hydrocarbon evolution in North China.It indicates that the evolution of the Paleozoic basinswasmainly controlled by the transition of ocean-continent tectonic system at the edge of North China plate and basins were formed mainly in the marginal area of the craton.The prototype basins developed along themargin of craton in the Early Paleozoic were passive continentalmargin，active continentalmargin and collisional continentalmargin successively.The Cambrian and Ordovician source rockswere developed in passive continentalmargin basins，aulacogen and intraplatform depressions under extensional mechanism.The Permo-Carboniferous basins in the Late Paleozoic were mainly controlled by the extension of theNorth China continentalmargin and transgression ofdifˉferent directions in different periods，form ing coal stratum and source rockswhich were different in the east and west ofNorth China.TheMeso-Cenozoic basinswere concentrated inside the craton andwent through four important tectonic evolution stages，presenting a pattern featured by a W-E zonation and S-N blocking partition.Many kinds of prototype basinswere formed and then stacked or juxtaposed under different tectonic backgrounds such as compression，extension strike-slip and subsidence，transform ing the Paleozoic basins into block uplifts or depressions.Due to a differential superimposition of the Meso-Cenozoic basins，the Paleozoic strata went through two different hydrocarbon generation processes，one is a continuous hydrocarbon generation and the other is secondary hydrocarbon generation during theYanshanian and H imalayan inNorth China.Located in areas favorable for secondary hydrocarbon generation of the Upper Paleozoic source rocks，the Jiyang sag，the east of the Linqing sag in BohaiBay Basin and them iddle and eastof the Zhoukou sag in the southernNorth China are considered good exploration targets for hydrocarbon accumulations.

Characteristics and timing of faults in Luositage area, the western Tarim Basin

2010, 31(6):  795-801.  doi:10.11743/ogg20100612

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:Detailed interpretations of seismic profiles are carried out for analyzing features in the Luositage area，western Tarim Basin.The results reveal that the deep Haimi-Luositage fault is a strike-slipping-oblique thrust fault.Towards the east，the faultbeltbecomeswider and its inner configuration getsmore complex alongwith the intensification of thrusting.TheNW-striking segment of the fault is dom inated by dextral strike-slipping and acts as a relay structure.This fault activated in the Cretaceous-Early Paleogene when it thrusted northwards and ceased downwards in the Lower-Middle Cambrian salts.The contemporaneous Shalong fault thrusted southwest-wards and were deeply involved in the basement.The shallow Haim i-Luositage fault thrusted northwards during the Pleistocene and ceased downwards in salts at the bottom of the Paleogene.The Luositage area，situated in a relay zone where the southern boundary faultof the Bachu faulted uplift changes from nearEW striking into near NW-striking，is not a good place for the development of faultˉrelated structureswhere hydrocarbons can accumulate.Therefore，it is probably not a favorable lead.

Characteristics and controlling factors of pore features in the Putaohua oil reservoir in the B lock Zhao-35，Daqing oilfield

2010, 31(6):  802-809.  doi:10.11743/ogg20100613

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A statistic analysis of lithology，thin section，SEM observation and mercury injection data reveals the physical properties and pore structures of the reservoirs in the study area.It suggests that the Putaohua reservoir is characterized bymedium porosity and m iddle-to-high permeability.Its pore types include normal intergranular pores，reduced intergranular pores and intragranular dissolved pores.The reservoir also features in low displace-ment pressure，low median capillary pressure，well-developed m icroscopic pore structure，and medium-to-large pore throat.Five parameters，namely the porosity，permeability，displacement pressure，mean pore throat radius and mercuryˉinjection saturation，are used to classify the reservoirs in the area into four types.TypeⅠhas large pore and wide throat;typeⅡhasmedium pore and medium throat;typeⅢhasmedium to small pore and small throat;and typeⅣhas small pore andm icro throat.They are supreme，good，fair and poor reservoirs respectively.The reservoir qualities are controlled by sedimentation，compaction and cementation，amongwhich sedimentation is predom inant.Reservoir quality of underwater distributary channel sand is the best.

REE models for the discrim ination of fluids in the formation and evolution of dolom ite reservoirs

2010, 31(6):  810-818.  doi:10.11743/ogg20100614

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Based on studies of fluids in formation and evolution of dolom ite reservoirs with REE in recent years and in combination with REE analyses of typical samples from the Sichuan and Tarim basins，fourmajor REE models are presented to identify the sources and behavior characteristics of fluids.（1）REE modelwith dolomites weakly altered by diagenetic fluids still showing seawater origin.It is characterized by lowwhole-rock gross REE content（generally<20μg/g），significant positive Ce anomaly，LREE enrichment，and relatively flat HREE distribution patterns;（2）Meteoric water leaching-percolation REE model.It features in whole-rock REE content being lower than thatofnormal dolom ite，positive Ce anomaly significantly lowering and even turning into negative Ce anomaly，and calcite veins ofmeteoric water leaching origin being the lowest in REE content;（3）Diagenetic fluid-hydrocarbon fluids REE model.It is characterized by slightly lowering whole-rock REE content but sim ilar distribution patterns as seawater.The associated dolom ite overgrowth has relatively higherREE content and Ce SWN value.Calcite veins ofdiagenetic fluid origin have significanthigherREE content and Ce SWN value than thatofhost rock.However both of them show the characteristic of seawater origin;（4）Hydrothermal alteration model.It features in lowerREE content，positive Eu anomaly and undulating REE distribution patterns.

New knowledge of gas source rocks in the m arine sequences of South China and relevant index system for tracing

2010, 31(6):  819-825.  doi:10.11743/ogg20100615

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Simulated experiments and geochem ical analyses of different types of hydrocarbon sources（source rocks，solid bitumen，asphaltic sandstone，crude oil/oil seepages）inmarine sequences ofSouth China reveal the coexistence ofmultiple hydrocarbon sources and theirmutual transformation and continuous or overlapping hydrocarbon generation.Marine source rocks in South China commonly feature in a state conversion of gas-generating parentmaterials and a relay of hydrocarbon generation process，presenting a characteristic that can be described as“coexistence ofmultiple sources and continuity ofmultiple gas generating phases”.An index system for tracing is established in accordance with such effects as the parentmaterial inheritance，isotopic fractionation and accumulation.It is based on stable isotopic components and important tracingmeans such as composition，biomarker，light hydrocarbon，nonˉhydrocarbon gases as well as rare gas isotopes and trace elements，and can be used to trace the process of transformation of different sources and hydrocarbon generation.The ternary tracing system of gas generation and accumulation is further improved.This paper presents a gas source rock tim ing model，gasˉsource correlationmethod，identification index of gas origin and their tracing，aswell as a prelim inary model for source identification and quantification ofm ixed gas.

Ultramicroscopic organic petrology and potential of hydrocarbon generation and expulsion of quality m arine source rocks in South China

2010, 31(6):  826-837.  doi:10.11743/ogg20100616

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Choosing samples of qualitymarine source rocks in various strata in South China，we make a study of mineral composition，correlation between organic matter and mineral composition，occurrences of organic matter，hydrocarbon-generating organism and features ofhydrocarbon generation and expulsion byways such aswhole rock X-ray diffraction，combined scanning electronmicroscope and energy spectrum，and simulated experimentof hydrocarbon generation and expulsion.The results show that minerals such as quartz，calcite and dolomite in these source rocks are mainly biogenetic or related to biogenetic origin.The total organic carbon content has a positive correlation with the quartz content but a negative correlation with clay minerals content.We believe that organic matter in these source rocks have threemain occurrences:1）organicmatter associated with siliceousmatter.It is the major occurrence in the qualitymarine source rocks in South China;2）organicmatter associated with calcareousmatter.It is the main occurrence in some quality calcareous source rocks in the Permian;3）organic matter associated with clay，or coated by flaky clay particles and associated with siliceous and calcareous bioclastics.In this case，the occurrence of organic matter is mainly controlled by depositional setting and sedimentary facies.There are mainly three kinds of hydrocarbonˉgenerating organisms:algae，benthos and fungus.Samples from the same layer of source rocks commonly contain multiple parentmaterials.According to the simulated experiments，the hydrocarbon-generating potential of floating algae is the same as TypeⅠkerogen，while that of benthos is the same as TypeⅡkerogen.Super thin siliceous or calcareous layers rich in organic matters are easy to expel early-generated heavy oil，and thus a giantheavy oil poolmay be formed.In contrast，organicmatter coated by flaky clay particles are hard to expel early-generated heavy oil，and thus a light oil poolmay be formed.

Application of geochemical parameters in hydrocarbon m igration studies: taking Tazhong area of the Tarim Basin as an example

2010, 31(6):  838-846.  doi:10.11743/ogg20100617

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Hydrocarbon migration in the Tazhong area of Tarim Basin is studied through geochem ical tracing based on analyses of saturated hydrocarbons，aromatic compounds，nitrogenous compounds and trace elements of fluid inclusions.The result reveals that both vertical and lateral hydrocarbon migration are common in the study area.Faults here are the effective verticalm igration pathways，while unconform ities and connected sand bodies serve as the lateralm igration pathways.The exploration success rate can be improved by studying vertical hydro-carbon migration through integration ofgeochemical datawith geological data and selectingmultiple targets based on an analysis of faulting history.Analysis of lateral carrier systems for lateral hydrocarbon migration indicates that excellent reservoirswith certain tectonic settings are dominant pathways forlateral hydrocarbon migration.Therefore，the relative structural highs of these quality reservoirs are favorable for hydrocarbon accumulation through lateralm igration.

A discussion on methods of play assessm ent

2010, 31(6):  857-864.  doi:10.11743/ogg20100619

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According to exploration maturity and oil/gas discoveries，plays are divided into three categories，namely play in appraisal，play in prelim inary prospecting，and play in regional prospecting.Appraisal parameters are selected according to probability of obtaining a discovery and strategic value of petroleum resources.Templates are built for evaluation of theses three types ofplays by using these parameters，and corresponding quantitative indices and parameter systems are also established.W ith theses templates，sim ilar plays in different regions can be appraised and selected on the same platform according to the same standards.

Method for appraising hydrocarbon resource potential in relict m arine basins in China

2010, 31(6):  865-870.  doi:10.11743/ogg20100620

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According to the theory ofmobilism and the idea of“prototype basin controlling hydrocarbon sources and superimposition of basins controlling hydrocarbon accumulation”，we studied the formation and evolution of continentalmarginal and intracontinental basins during the geological histories of the ancient Chinese Continent，the ancientAsian Continent and the new Asian Continent，and probed the TSM basin modelingmethod for resource evaluation in Chinese relict Paleozoic marine basins.Vertically，3sets of source rocks including the Lower Cambrian，the Middle-o-Upper Ordovician-Lower Silurian and the Perm ian were developed in Chinese Paleozoic marine basins.The LowerCambrian source rockswere developed on the landside ofpassive continentalmargin，the Middle-to-Upper Ordovician-Lower Silurian ones in intraplatform depression and the Perm ian ones in intracontinental rifted-downwarping basins.Depressions on passive continentalmargin were themost favorable for developmentof source rocks.There aremainly two types of source rocks，namely carbonates and argillites.Through prototype basin-constrained quantitative mathematical modeling of geologic process-hydrocarbon responses，we performed network integration and appraisal of petroleum resource potential.The development of the Paleozoic marine prototype basins and their later superimposition and evolution as well as their petroleum significances are discussed.This method has been successfully applied to the appraisal of the Upper Paleozoic source rock potential in North China.

Quantitative forward m odelling of cavity volume in carbonate reservoirs in Tazhong area

2010, 31(6):  871-878,82.  doi:10.11743/ogg20100621

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In this paper，we discuss key issues constraining exploration and development of carbonate reservoirs in the Tazong area such as analysis of seism ic response characteristics and calculation of cavity volume by using wave equation forward modelling.Through many forward modellings，we figure out the geological implication of various complex seism ic responses such asmoniliform high amplitude，mutton chop-shaped high amplitude，chaotic reflection and low amplitude.We also bring forward a new method for calculating cavity volume with forward modelling correction.The study shows that this method is an effective way to calculate cavity volume of carboˉnates and can provide help for efficient development and reserve estimation.

A conceptual model for extrapolating interval velocities of deep layers based on the pressure compartment model

2010, 31(6):  879-882.  doi:10.11743/ogg20100622

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In a basinwith pressure compartments，true interval velocity of layers beyond the reach ofdrilling can not be obtained by using velocity spectrum when the velocities obtained from velocity spectrum in the pressure compartments are very different from themeasured velocities during drilling（for example sonic logging）.In this case，the interval velocity of deep layers beyond the reach of drilling can be extrapolated based on“pressure compartmentmodel”.The basic formula for extrapolation can be expressed as the functional relation between formation pressurewithin the pressure compartments and interval velocity.First，the theoretical interval velocity of the first layer beneath the bottom hole is calculated by using the functional relation，and then the theoretical interval velocity of the second layer beneath the first layer is calculated，and the rest can be obtained in the samemanner.