| The middle-shallow strata in Nanpu Depression is Ed2 and above.The two main sets of source rocks are the lower Sha3 formation,Shal formation and inside Ed3.Reservoir develops in all formations of the middle-shallow strata.It is a typical source-reservoir-cap form named lower source-upper reservoir.The fault is a necessary way to transport oil and gas from the bottom up.And it is a bridge connecting accumulation elements such as source rock,reservoir,caprock and trap and so on.The drilling data in the study area reveals that oil and gas reservoirs which have been found are all associated with faults,having the characteristics of the distribution of multi-layer.But not all the traps which are associated with faults have been found oil and gas in them.In order to explore the special distribution law of oil and gas in the study area,the fault analysis is the main line in this paper,combined with other accumulation element analysis such as source rock,reservoir,caprock and trap.To look for the main space matching relationship controlling hydrocarbon accumulation,start with finding the matching relationship in space between the fault and other elements.Using seismic interpretation data and many methods such as growth index profile,fault activity rate,elongation of section,combined profile,tectonic evolution profile,a profound analysis on the formation and evolution history of fault has been made in the study area.It is concluded that the faults in Nanpu Depression have the "three times three features" evolution characteristics from the period of Shahezi deposition to the present,stretching in the early stage,striking and slipping in the medium stage,and tensile shearing in the late stage.Using geochemical data,drilling,logging,seismic data,combined with the results of previous studies,through structural analysis,sedimentation analysis,laboratory analysis and other means to study accumulation elements such as source rock,reservoir,caprock and trap.The results show that there are two sets of source rocks in the middle-shallow strata in Nanpu Depression,which develop in the formations of S Es3 and Es1-Ed3,The reservoirs exist in from Ed2 to Nm.The caprocks are 3 sets.Two sets are regional mudstone caprocks,which are in the upper Ed2 and the lower Minghuazhen formation.And one set of local volcanic caprock,which is in Guantao3 formation.On the second structural zone,traps mainly develop faulted anticlines,broken noses,fault block traps.And single trap has three types:fault block,broken nose,faulted anticline traps.On the basis of study accumulation elements,such as fault,source rock,reservoir,caprock and trap,with methods of determining oil source fault,caprock disconnect thickness,fault-sand lateral shunt conduit coefficient,fault dense belts division used,space matching relationships are carefully analyzed including fault-source,fault-sand,fault-trap.It is concluded that:(1)Fault-source matching relationship:according to the cutting relationship between faults and 2 sets of source rocks,3 different types of matching relationship are divided:fault-double source,fault-single source,fault-indirect source.The quantity of oil and gas reservoirs is the largest which are controlled by fault-double source type.Combined with the distribution of oil and gas reservoirs,fault-source matching relationship controls the distribution range of the oil and gas reservoirs,(2)Fault-sand matching relationship:according to the matching relationship between inclination of the fault and inclination of sand both sides,4 types are divided:antithetic normal fault type,same direction normal fault type,ridge normal fault type and anti-ridge normal fault type.Anti-ridge normal fault type doesn' t develop in the study area.The hanging wall of antithetic normal fault can match well with footwall of same direction normal fault type.Transporting oil and gas capability of lateral diversion index,which is used to evaluate the matching relationship between fault and sand,is built by using contact length of fault and sand,thickness of sand body,dip of sand body,dip of fault,clay content.It reveals that the higher the index is,the higher the degree of hydrocarbon enrichment.Conducive to the lateral diversion of oil and gas when its value is greater than 2.Mathematical statistics is done on the relationship between the hydrocarbon content and sandstone thickness and stratigraphic thickness ratio in each formation in multiple wells in study area.The result shows that the ratio of the formation should be greater than 20%,which is conducive to oil and gas lateral diversion.(3)Fault-caprock matching relationship:According to the degree of the caprock being cut by fault,3 types of fault-caprock matching relationship are divided:failure to disconnect type,fully effective type,partially effective type.Through the relationship between the disconnect thickness of caprock from small to large and the distribution of oil and gas in depth in multiple wells,it can be conclude that the oil and gas distribute above and below the caprocks both,if the caprocks'disconnect thickness is small;and the oil and gas distribute below the caprocks only,if the caprocks' disconnect thickness is large,which has an obvious control effect on the vertical distribution of oil and gas.The caprock disconnect thickness in the transition zone where oil and gas distribute both above and below the caprock to where only below the caprock is the threshold of fully effective type and partially effective type.Hereby the threshold of 2 sets of caprock the upper Ed2 formation and Ng? is 90?95m and130?150m.Three modes of fault-caprock matching type controlling the oil and gas vertical distribution are established for Ed2 and Ng? caprock:(?)seal below not seal above type,(?)seal above not seal below type,(?)not seal both above and below type.Oil and gas can only accumulate below the Ed2 caprock in type ?,And the upper caprock has no sense.Oil and gas can accumulate both above and below Ed2 caprock in type ?,while it can accumulate both above and below Ed2 and Ng? caprock in type ?.(4)Fault-trap matching relationship:According to the location of traps relative to fault dense belts,3 types of fault-trap matching relationship are divided:anticline-internal fault trap,anticline-edge fault trap,syncline-internal fault trap.From the observation to the distribution of the hydrocarbon range and these three matching relationship types,they can all control the effective accumulation of oil and gas.And oil and gas accumulations which are controlled by anticline-internal fault trap type and anticline-edge fault trap type have greater numbers and higher rich degree.At the same time,according to the relationship between fault inclination and inclination of strata in traps,2 classes of fault-trap matching relationship are divided:antithetic fault-trap matching,same direction fault-trap matching.Each is divided into 3 types:single fault-trap matching type,double faults-trap matching type and multiple faults-trap matching type.Contrasting the 6 types in 2 classes with the quantity of hydrocarbon reservoirs,oil area and reserves abundance,we find that antithetic fault-trap matching type has an important leading effect on oil and gas accumulation.And double faults-trap matching type and multiple faults-trap matching type in same direction fault-trap matching type are better type.On the basis of space matching relationship,such as fault-source,fault-sand,fault-caprock,fault-trap in middle-shallow strata in Nanpu Depression,combined with fault-source matching relationship controlling the position where oil and gas accumulates,fault-caprock matching relationship controlling the range of oil and gas vertical distribution,fault-sand matching relationship controlling the formation of accumulation,and fault-trap matching relationship controlling the location of hydrocarbon accumulation,a hydrocarbon accumulation model is built which is applicable to up reservoir-down source type oil and gas combination.It has a significant sense in recognizing hydrocarbon enrichment rules and in exploring hydrocarbon in up reservoir-down source type field. |
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