物探新技术：AVO处理技术
New Geophysical exploration technique-AVO Processing Technique
AVO(Amplitude Versus Offset)是利用振幅随偏移距变化特征分析和识别岩性和油气藏的地震勘探技术。通过AVO技术，可以提取高精度的岩石物性参数，有利于资料的综合解释和油气预测，提高探井成功率和合理制定开发方案，从而降低勘探风险，提高经济效益。
AVO is a seismic exploration technology using the characteristics of amplitude variation versus offset to recognize the rock types and oil-gas reservoir. It is capable to obtain the parameters of rock properties in high quality through AVO survey, which is favorable to make a synthetic interpretation and prediction of the oil-gas deposit, give rise to success of drilling, make the right decision of exploration, reduce the risk of the exploration, and increase economical benefit.
地震岩性分析方法有两种：一是建立在叠后地震资料基础之上的地震属性和地震振幅分析方法，二是建立在叠前地震资料基础上的地震属性和地震振幅分析方法，这种方法通常称为AVO分析。
There are two types of the analyzing seismic rock properties: one is the seismic property and amplitude analysis based on the poststack seismic data; the other is one based on the prestack seismic data, the latter is referred as AVO analysis.
AVO分析的基本方法分为正演和反演。AVO正演方法是利用模型正演模拟AVO现象，结合油藏特征，分析不同地质条件下，油、气、水等气流体所产生的AVO特征，建立相应的AVO监测标志，在实际地震记录中直接识别岩性及含油气。正演方法一般用于定性的油藏描述。AVO反演方法是能更为合理地提取隐藏在地震信息中的岩性参数，预测岩性和烃类的重要途径。它根据振幅随入射角变化关系，由实际地震道记录估算岩石的地震参数。
The basic methodologies of AVO analysis can be classified into forward modeling and inversion. The forward modeling in AVO is to simulate the AVO phenomenon, which is able to incorporate with the features of oil deposit, analyze the AVO characteristics produced by the gas-liquid mixture in the different geological environment, establish the corresponding AVO monitor index, and finally recognize the rock properties and locate the oil-gas deposit directly. The forward modeling of AVO is generally used to qualitatively outline the oil deposit, while the inversion of AVO is a critical approach to extract rock parameters concealed in the seismic information, and predict rock properties and hydrocarbons. It estimates the seismic parameters using real seismic data gathers through the amplitude variation with respect to the change of incident angle.
地震波反射振幅的变化受诸多因素的影响和控制。研究人员发现，AVO的关键是要恢复叠前地震数据的地震振幅，来反应地下实际的岩性及含油气性。因此，AVO处理是AVO分析研究的关键，处理流程及参数的合理与否直接影响分析结果。在AVO处理时要注意：一是要恢复地震波在地下传播中所受到的各种能量衰减和畸变；二是利用AVO道集记录提取各种反映岩性和油气信息的叠前地震属性(AVO属性)。
The amplitude variation of reflection were influenced and controlled by many factors. Researchers discover that the key issue in AVO is to use prestack seismic data to recover the amplitude, which reflect the properties of rock and oil-gas. Therefore, the AVO data processing is critical in AVO analysis, while data processing and suitable parameter selection directly influences the results. Note that in AVO data processing it is important to recover various kinds of wave energy attenuation and distortion, and then extract the prestack seismic properties (AVO properties) reflected by the rock and oil-gas information through AVO data gathers.
与常规地震处理相比，AVO处理有三点不同：一是振幅处理要求高，它包括与偏移距有关的球面扩散和吸收补偿，应避免使用单道均衡，以免引起虚假的AVO现象。二是强调地表一致性处理，包括地表一致性反褶积、振幅补偿和静校正。三是AVO处理还增加了一些与AVO信息提取、异常显示、检测和增强的特殊处理。目前，研究院已形成了它包括高保真、保幅地震资料处理技术，异常振幅识别技术，模型正演及弹性反演技术等技术系列。
Comparing with conventional seismic processing, AVO processing has three different procedures: (1) there is a high performance required in the amplitude produce, which includes spherical diffusion and absorbance reduction relative to the offset, and the single fold equilibrium should not be used so as to avoid creating false AVO phenomena. (2) There are emphases on consistent processing of the surface of the earth, which involve consistent deconvolution of surface of the earth, amplitude reduction and static correction. (3) There is specific processing with respect to information extraction, detection and enhance. So far, the research college developed a series of techniques including high fidelity and real amplitude of seismic data processing, anomalous amplitude recognition, forward modeling and elastic inversion.
20世纪70年代“亮点”技术的出现,使地震烃类检测能力有了很大提高。80年代初,Ostrander (1982年)首先提出利用反射系数随入射角变化识别\"亮点\"型含气砂岩，他注意到：含气砂岩反射振幅随偏移距增加而增加，含水砂岩反射振幅随偏移距增加而减少，这一现象的发现丰富了烃类检测的技术。Ostrander的发现也标志着实用的AVO技术的出现,激起人们对AVO现象的极大兴趣, 人们开始把AVO信息应用于研究中。Gassaway等人把AVO信息用于反演泊松比，直接解释岩性和油气；Shuey对Zoeppritaz的P波反射系数进行简化，提出抛物线表达式,这使得AVO属性分析和零偏移距剖面的提取得到广泛应用； Smith（1987年）等提出用加权叠加方法估计流体因子和检测气层。
The advent of “bright spot” technique in the 1970s made a great improvement in the seismic hydrocarbon detection. In the early of 1980s Ostrander (1982) first put forward the “bright spot” technique to recognize gaseous sandstone by using the variation of reflected coefficient with respect to the change in incident angle. He noted that the reflected amplitude of gaseous sandstone is increased, but the reflected amplitude of watered sandstone is decreased with the increase of the offset distance, which enriches hydrocarbon detection. Ostrander’s discovery was the indication of the advent of real application for AVO technique, which excited a great interesting in the geophysical society to have it be applied in the research. For example, Gassaway et al applied it into inversion of Poisson's ratio to directly interpret rock property and oil-gas, Shuey simplified the Zoeppritaz’s reflected coefficient of P wave, and put forward a parabolic expression, which made wide application of AVO analysis and extracting zero-offset seismic profile, Smith et al. (1987) brought up an idea to estimate liquid factor and detect gaseous layer by using weighted fold method.
为了充分挖掘AVO信息的潜力，不少研究人员还研究用AVO属性（斜率和截距）交汇图识别岩性和油气，并提出AVO烃类检测因子。AVO的提出最初仅仅是为了提高烃检测能力，今天AVO的发展已经超出了这个范畴，它已经和正在渗透到地震勘探的各个领域。在裂缝检测、压力预测、油藏动态检测、油气预测、储层非均质性描述方面得到广泛应用。
In order to potentially use AVO information, even a few researchers studied AVO property intersection map to recognize the rock formation and oil-gas, and hence put forward an AVO hydrocarbon detection index. AVO was primarily put forward to improve the ability to detect the hydrocarbon, but today it develops much beyond of this scope, and permeates every aspects of seismic exploration. It is widely used in the fissure detection, pressure prediction, dynamic reservoir monitor, oil-gas prediction, stratum’s non-uniform depiction.
