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Seismic Attributes Analysis of Sha2-dongying Group in WenĄŻan Slope of Baxian Depression

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Tutor: ChenGongYang
School: Yangtze University
Course: Mineral prospecting and exploration
Keywords: seismic attribution,fluvial sand body,reservoir predication,WenĄŻanslope,Baxian d
CLC: P631.4
Type: Master's thesis
Year:  2012
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Abstract:
WenĄŻan slope, located in Jizhong depression of Eastern Sag, is inclined from the southeast towards northwest. Baxian depression is a Mesozoic and Cenozoic downfaulted basin. The strata developed a bottom-up sequence of Kongdian group, Shahejie group, Dongying group, Guantao group, Minghuazheng group and Quaternary layer. The research explained in this paper mainly focus on the Sha2in Shahejie to Dongying group. Sha2group is dominated by interbedded light grey or greenish grey sand and mauve mud, locally developed gypsum rock. This is the deltaic braided river deposit. The lower section of Sha1is composed of grey mud imbedded with oil shale, shale, thin biolithite limestone and dolostone. This lithological character indicates a lake depositional environment. The upper section of Shal includes grey and dark grey mudstone interbedded with few sandstone. This implies a braided river system. The major lithology of Dongying group is characterized by interbedded sand and mud which show evidence of a meandering river depositional environment. The whole target section can be divided into3sections. They are Sha2, lower section of Sha1and the upper section of Sha1and Dongying group. The3sections are dominated by long term asymmetrical uptrend hemicycle. The middle lower part of each cycle is the developmental section of reservoir sand bodies. WenĄŻan slope is an inherited depositional slope. It composes of three wide, gentle, nose shapedslope structure, they are Zuogezhuang, WenĄŻan chengdong, changfengzheng which distributes from north to south. Although the local faults are well developed, the trend of these faults is almost parallel to that of the ramp region. Large scale structural traps cannot be developed. Also, fluvial facies is predominant in the target strata of reservoir. The formation of reservoir is controlled by tectonic setting of slopes and the sideway piching of channel sand bodies. These controlling factors, together with the frequent transverse sway and lateral deposition of multiple channel occurrences, make the transversal continuity of reservoir extremely poor. These problems significantly create difficulty to exploration within the target region. Therefore, it is difficult tocontrol and predicate the distribution of reservoir based solely on well data due to the complexity and diversity of the fluvial reservoir. In order to solve this, the advantage of lateral continuity of seismic information has to be well-applied. With the calibration of well data, the fluvial reservoir prediction and investigation could be made. Aiming at these difficulties, the prediction of reservoir mainly focusing on the technique of seismic attributes analysis has been carried out and discussed in this paper. The technique of seismic attributes analysis meets the need of reservoir description and3D seismic data volume, particularly for the description of heterogeneous reservoir. The basic idea emphasizes the correlation calculated from the log information, seismic trace next to well and seismic attributes. And then, based on these results, the characteristics of reservoir in area which lacks of wells or locates between wells can be predicated, namely seismic-guided log parameter appraise. The main computational method aims at calculating event amplitude, frequency, frequency spectrum parameters in every seismic channel, such as addition, average, differentiation etc. By utilizing these methods, the parameters which are sensitive to the actual geological conditions can be obtained and expressed directly to guide exploration.By using the Epos3.0software from Paradigm Company, the paper has given a research on automatic tracking interpretation for3D seismic data volume, extracting correlated horizon attribution and extracting correlated interval attribution by Stratimagic. After dimensionality reduction analysis and artificial optimize, a group of parameters layout matched with reality geologic situation can be obtained. Finally, classification of these seismic attribute parameters can be classified by using the technique of neural network. On the basis of comparing with the result of classic depositional facies analysis, the delta deposit, lake facies,ĄŻcharacteristics of fluvial facies on the group of Sha2to Dongying in WenĄŻan slope can be predicated.This paper mainly study the amplitude, frequency and wave impedance attribute. The results show that:ąÙinterpretation of the change of lithology, physical properties and electrical parameters of each sub-layer in layers can be made. Particularly, it can be used to identify the channel sand bodies and boundaries, delta sand bodies, faults, unconformities, fluid mutations and other geological information. For thinner layers, more sensitive parameters in small time gate, such as the reciprocal of amplitude, can be applied;ąÚfrequency can analyze the transverse changes of crest and trough, so it can reflect the change of rockĄŻs thickness, lithology and lithofacies;ąÛthe change in wave impedance attribute can show the distribution of the sand bodies, the value of wave impedance can reflect the thickness of a coplanar sand body;ąÜthe information of the parameters above can be used to classify the seismic facies by artificial neural network. This method is used to characterize the the trace of data by seismic waves. According to the value of classification, the classification of model trace can be determined, and then, the waveform of each trace is classified by artificial neural network. The repeated seismic facies waveforms are classified into the same model trace, namely data training process.ąĘBy comparing the waveform of uphole trace to the model trace, analyzing the correlation of each trace, a computing mode for the reservoir prediction of cross-well and no-well area is established. This paper mainly uses the amplitude, frequency and wave impedance attributes to analyze the seismic facies of WenĄŻan slope.By combining research and data processing and interpretation, the following characteristics are concluded:(1)The study of reservoir geological origin using seismic attribute analysis can be seen as the foundation of reservoir prediction. The lateral deposit formed by channel sand body creates a characteristic of short-axis low-frequency seismic reflection. The seismic balanced amplitude slice expresses the discontinuity on plane. This effect is better in meandering river than that of braided river apparently. The high amplitude of peaks and troughs of seismic wave represent the distribution of the fluvial sand body and the water system.(2)The amplitudes fourth derivative is sensitivity in response to the weak change, so it can identify the channel sand body easily, especially for carving the distribution of the channel bed.(3)The channel deposit is characterized by low frequency seismic reflection, the distribution of fluvial sand body was corresponded with the area of frequency lower than lOHz.(4)Based on the waveform analysis technique with neural network, we can overcome the ambiguity and uncertainty brought by single parameter in seismic attribution. Through calibrating with well data, the results of classification had high correspondence with the recognition of geology.
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