High-resolution sequence stratigraphy features of the river facies reservoir in the Fanjiachuan oil field
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The rive facies reservoir is short of symbol layer and sandbody is folded and picked ,so fine isochronous sandbody comparing and dividing are difficult. On the basis of the theory of the base-level cycle, 7 short-term cycle sequence,3 middle-term cycle sequence,2 long base-level cycle sequence can be distinguished from the Y8~Y10 oil formation of the principal oil-bearing ones in the Yanan Formation of Middle Jurassic age. The base-level cycle sequence is corresponding to different grade genetic units. At the same time, all graded sequence structure types,stacking patterns and chrono-stratigraphic framework are established on the basis of the middle-term cycle sequence, and short-term cycle sequence,and the reservoir distribution by the different base-level cycle is discussed.Keywords:
Sequence Stratigraphy
Sequence (biology)
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The high-resolution sequence stratigraphy theories and technologies are widely used in the exploration and exploitationof subtle lithologic gasreservoir, taking it as a direction ,through dynamic analysis on base-level cycle structure and stacking pattern , combined with the comprehensive studies of outcrops, cores and well logs,two long-term, five middle-term and fourteen short-term cyclic sequences from the lower Shihezi Formation of Su 6 well area in Sulige gas field are classified. the structure types, sedimentary cycles, stacking patterns of short-term, middle-term, long-term cyclic sequences and the relationship between cyclic sequences and distribution of favoringsand are discussed in detail. A chrono-stratigraghic frameworkis established by reference to thelong-term and middle-term cycle sequences, in which the characteristics of differenttype of sand are discussed in detail. Based on the division and correlation of individual-sandbody correspondto short-term cyclic sequence,directing by the method of lithofacies-paleogeographical mapping, the sedimentary facies and sand distribution maps of the short or middle-term cyclic sequences come into being , the distribution of favoringsand reservoir can be predicted.
Sequence Stratigraphy
Lithology
Outcrop
Sequence (biology)
Natural gas field
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The high-resolution sequence stratigraphic theories, and the methods of wavelet analysis and frequency spectral analysis were used to define the sequence stratigraphic framework of the Upper Triassic Yanchang Formation, which have five long base-level cycles and 21 to 25 middle base-level cycles. Based on studying the relationship between the sequence stratigraphic chronostratigraphic framework and reservoir development, it is found that the development and distribution of reservoir has been apparently controlled by the A/S and boundary of sequence stratigraphy of Yanchang Formation. Sandstone reservoirs with relatively good properties occurred mainly at the early stage of the ascending long base-level cycle and the late stage of the descending middle base-level cycle, especially at both sides of the interface of long-term base level cycle and middle-term level cycles. Sour fluids migrate along the interface, favoring the formation of induced porosity, which can improve the reservoir. Compared with traditional method, this method can eliminate the uncertainty of artificial division of sequence, improve precision and accuracy of cycle division and correlation, and improve the success rate of oil and gas exploration.
Sequence Stratigraphy
Sequence (biology)
Stratigraphic unit
Petroleum reservoir
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The different base levels of cycles in the lower sub-member of Es2 in Wen 99 fault block reservoir in Dongpu depress were studied based on the principle and methods for high resolution sequence stratigraphy and the data from the well logging and core sample.1 medium-term stratigraphic base level cycle and 5 short-term stratigraphic base level cycles and 19 super-short-term stratigraphic base level cycles were recognized in this area,and a further discussion on sequence structure and stacking pattern of short-term stratigraphic base level cycle was given in this paper.Meanwhile,on the basis of single well analysis,higher accuracy isochronostratigraphic correlation was done at the different order base level cycles,for which half time unit boundary was selected as optimum correlation marker,and in the end a sequence stratigraphic framework of the lower sub-member of Es2 was built.
Sequence Stratigraphy
Sequence (biology)
Base (topology)
Fault block
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Through the comprehensive analysis of outcrops, cores, well logs and seismic interpretation data, and under the guidance of the theory and technology of the high resolution sequence stratigraphy initiated by Timothy A Cross in 1994, the characteristics of the different grade sequence interface and laucstrine flooding surface in the second member of Nadu Formation Eocene in Lun 35 Block of Ziyin Oil Field from Base Basin are studied. According to the identification sign of the sequence interface and flooding sedimentation, four grade base level cycle sequences that are divided into 13～18 supershort term, 7～9 short term, two middle term, and one long term cycle sequences are recognized from the formation. On the basis of these studies, the vertical sequence, facies association, lithologic component, structure type and stacking pattern are discussed in detail. Among these sequences, the supershort term and short term cycle sequence may be divided into two basic types of structure which are up deepening non symmetry and symmetry from up deepening to up shallowening.The first can be divided further into two subtypes of low or high accommodation and the second can be devided further into three subtypes of non complete or nearly complete symmetry. These basic sequence types and subtypes are of various stacking and distribution patterns. The structure type and stacking pattern of the middle term cycle sequence are the same as that of the short term cycle sequence. The long term cycle sequence are of non complete symmetric structure which develop complete depositional sequence of lacustrine transgressive regressive cycle, and thickness of rising half cycle is larger than the falling half cycle. According to the high resolution isochronous stratigraphic correlation of the turnround boundaries of different order base level including short and middle termcycle sequence, the sequence and time stratigraphic framework can be built that in the scale of supershort term base level cycle as an isochronous unit, which are of varied application significance in hydrocarbon exploration and development ,such as isochronous stratigraphic correlation of small sandbodies with oil, charting of isochronic microfacies in the large scale ,description of sandbody geometry, forecasting reservoir and petroleum accumulation, analysing reservoir heterogeneity, reservoir modeling and so on.
Sequence Stratigraphy
Sequence (biology)
Transgressive
Lithology
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High-resolution sequence stratigraphy division of Shanxi Formation in northwestern part of Ordos basin has been put forward according to principleof base level cycle based on 4 outcrops and 35 core description and 305 well logs. As a component of long-term base-level decreasing cycle, Shanxi Formation constitutes a medium-term cycle, which can be subdivided into 5 short-term cycles in ascending order(SSC1,SSC2,SSC3,SSC4,SSC5). Based on the sequence structure, and stack style and space variation, the high-resolution sequence stratigraphy correlation frameworkis established to discuss sedimentary facies styles and controlling factors and physicalproperty. The most favorable reservoir bodies were formed during early stage of semi-ascending cycle of short-term base-level cycle. Reservoir bodies are mainly composed of delta plain distributary channel and delta front sub-aqueous channel. Here, the mono-factor mapping method is adopted to study space distribution of the reservoirbed.
Sequence Stratigraphy
Outcrop
Sequence (biology)
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Gangdong oil field,claiming a history of 30 years, locates in Huanghua depression of Gulf of Bohai basin. Reservoirs of the oil field are to the fluvial facies deposits, and is extremely heterogeneous and layered. The reservoir mostly consists of small striped channel deposits interbedded with flood-plain. It is very difficult to correlate reservoirs. High-resolution sequence stratigraphic analysis can serve directly to high-resolution stratigraphic framework. First fault block, the second area of Gangdong oil fields is selected as the study area. Based on the principle of base-level cycles, two scales of stratigraphic cycles (short-and intermediate-term) are recognized through the combination of cores and logs data in the area. The short-term stratigraphic cycles, which maybe not relate to base-level cycle, are the result of channel avulsion autocyclic process, Five type of channel avulsion auto -cycles are identified. The intermediate-term stratigraphic cycles correspond to change of base-level cycle, and different types of the short-term cycles occur in different position of the intermediate-term base-level cycle. The same microfacies has different architecture in different position of the base-level cycle. The base-level cycle directly controll the channel reservoir geometry, Within an intermediate-term base-level cycle, during periods of low accommodation, channel deposits is mostly lateral aggradation, and channel reservoirs superpose and connecte each other. As accommodation increased, channel reservoirs become progressively isolated within flood-plain mudstone. According to that characterization, high-resolution sequence stratigraphic framework has been established based on intermediate-term base-level cycle, and using the high-resolution correlation to identify reservoir continuity and heterogeneities that could divide reservoirs into fluid flow compartments and are the most important factots in controlling the rates and pathways of fluid flow through reservoir.
Sequence Stratigraphy
Fault block
Growth fault
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The character of sequence boundary is summarized according to well log,seismic sections and rock cores in this paper.The distribution rules of sequence boundary and short-term cycle in difference sedimentary facies are studied alone from west to east.From Qingshankou Formation to Yaojiazu Formation,can be divided into 4 long term base level cycles and 10 short term base level cycles.Based on the fundamental principle of sequence stratigraphy and sedimentary,the sequence stratigraphic framework of the middle oil-bearing beds can server for future exploration and development.
Sequence Stratigraphy
Sequence (biology)
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In order to recognize the characteristics of fan delta facies reservoir and improve the reservoir description accuracy,this paper carried out the study on the reservoir of Upper Karamay Formation based on high resolution sequence stratigraphy and the strata cyclicity as well as sedimentology response caused by different grade base level change.The Upper Karamay Formation in Bai-21 well area can be divided into one long-term sequence cycle,two middle-term sequence cycles,14 short-term sequence cycles and 33～37 super-short-term sequence cycles.The short-term sequence cycles can be divided into two basic structure types which are up-deepening asymmetry and up-shallowing asymmetry.The sedimentary sequence,structure type,stacking pattern and distribution pattern of super-short-term sequence cycles in the process of base level change were discussed in detail.The sequence stratigraphic framework was built up by making short-term sequence as isochronous stratigraphic correlation unit.The sedimentary characteristics of sand body and the oil-gas distribution were analyzed.All these studies provide a good foundation for reservoir research and later development of Upper Karamay Formation in the Bai-21well area.
Sequence Stratigraphy
Sequence (biology)
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Through the comprehensive analysis of outcrops, rock cores,well logs, seismic interpretation and ESR data,and under the guidance of the theory and technology of the high-resolution sequence stratigraphy, this paper has dealt with different grades of sequence interfaces in Baigang Formation of Baise basin. According to the identification symptoms of the sequence interfaces and lake flood sedimentation, four-grade base-level cycle sequences, namely short-term, middle-term,long-term,super-long-term cycle sequences,are distinguished,and one super-long-term,eight long-term,twenty-one middle-term base-level cyclic sequences are recognized.On the basis of the above studies,the vertical sequences,facies associations,lithologic components, structural types and stacking patterns are discussed in detail.Among these sequences, the short-term cycle sequence may be divided into three basic types of structures, i.e., upward deepening non-symmetry, upward thinning non-symmetry and symmetry from upward deepening to upward thinning, and further divided into seven subtypes of low or high accommodation and non-complete or nearly complete symmetry. These basic sequence types and subtypes are of various stacking and distribution patterns. The structural type and stacking pattern of the middle-term cycle sequence are identical with those of the short-term cycle sequence. The long-term cycle sequence is of symmetric structure which develops complete depositional sequence of lacustrine transgressive-regressive cycle, and may be divided into three types of cycle structure in the light of the lacustrine transgressive-regressive rate, viz.,the fast rate type,middle rate type and fast rate transgressive-slow rate regressive type. In this paper the application of these different-grade base-level cycle sequences to the stratigraphic division and oil bed correlation, the foundation of sequence stratigraphic framework and the sand body distribution regularity are probed into in the light of these sequence characteristics.
Sequence Stratigraphy
Sequence (biology)
Transgressive
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Under the direction of theory and the technology of high resolution sequence of stratigraphy, the strata in middle-upper Trimassic in the 9th Area, Tahe oil field have been divided into fourteen 5-order sequence interfaces, which includes five long-term base-level cycles, fourteen middle-term base-level cycles and twelve short-term base-level cycles for down oil formation of primary objective reservoir. And three types of middle-term base-level cycle sequence architecture is built. Therefore by integrating into sedimentary analysis of every sequence unity and working out the old facies geographic map of sequence rock, a braided river delta-lake sedimentary system is developed, and it was found that the lake frequently advances and retreats, the upper-middle-down oil formation separates into the front edge of the delta and plant of the delta sediments. Thus the segment of mudstone delegates into floured-lake sediments.
Sequence Stratigraphy
Sequence (biology)
River delta
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