河流相储层不连续界限地震响应特征研究

储层不连续界限是指由于沉积作用、成岩改造及构造运动等因素,在储层中形成的岩性尖灭、砂体叠置、物性变化及小断层等对流体流动产生影响的各类界限统称,它是影响油田开发效果的重要因素之一。基于河道砂体的叠置程度,建立了考虑“厚度、高程、叠置范围”的河流相储层结构“三参数”概念模型及6类储层结构类型敏感属性图版;在此基础上,分析了“尖灭型、接触型、切叠型和叠加型”4类储层不连续界限地震响应特征。其中,尖灭型界限,地震响应表现为砂、泥岩的岩性变化特征,界限为岩性尖灭线,储层基本不连通;接触型界限,地震响应表现为砂岩厚度的变化特征,界限为“强—弱—强”的振幅类属性变化特征,储层具有一定的连通性但相对较差;切叠型和叠加型储层界限,地震响应表现为两期砂体叠置厚度与高程差的变化,由振幅类与波形类属性表征,在无明显夹层的情况下,储层连通性较好。储层不连续界限地震响应影响因素研究表明,时间采样率越小、主频越高、道间距越小,地震响应特征越明显。进一步,提出了基于储层结构平面分区的不连续界限预测方法,通过砂、泥岩相的识别,可以实现尖灭型界限的提取;通过砂岩岩相内地震属性的梯度变化求取不连续界限,基于界限及两侧的属性“强—弱—强”的相对关系,可以实现接触型和切叠型界限的识别。

Study on seismic response characteristics of fluvial reservoir discontinuous boundary

Reservoir discontinuous boundaries refer to various boundaries that have an impact on fluid flow and are formed by lithologic pinch out,sand body superposition,physical property change and small faults in the reservoir due to sedimentation,diagenetic transformation and tectonic movement.They are one of the important factors that affect the effect of oilfield development.Based on the superposition degree of channel sand bodies,a“three-parameter”conceptual model of fluvial reservoir structure considering“thickness,elevation and superimposed range”and a sensitive attribute chart of six types of reservoir structures are established.On this basis,the seismic response characteristics of four patterns of discontinuity boundaries,including pinch out pattern,contact pattern,overlap pattern and superposition pattern,are analyzed.For the pinch out boundary,the seismic response is characterized by lithological change of sand and mudstone,and the boundary is lithologic pinch out line,so the reservoir is almost disconnected.For the contact boundary,the seismic response is characterized by thickness variation of sandstone,and the boundary is characterized by amplitude attribute variation of“strong-weak-strong”,so the reservoir has a certain connectivity,but relatively poor.For the overlap and superposition boundaries,the seismic response shows the change of superimposed thickness and elevation difference of two sand bodies,and is characterized by amplitude and waveform attributes,so the reservoir connectivity is ideal in the case of no obvious interlayer.The study on the influencing factors of seismic response of reservoir discontinuous boundary shows that:the characteristics of seismic response become obvious with the decrease of time sampling rate,the increase of dominant frequency and the decrease of group interval.Furthermore,a discontinuous boundary prediction method based on plane partition of reservoir structure is proposed.The pinch out boundary can be extracted by identifying sand and mudstone facies;the discontinuous boundary can be obtained based on the gradient change of seismic attributes in sandstone facies,and the contact and overlap boundaries can be identified based on the relative relationship between boundary and“strong-weak-strong”attributes on both sides.