Seismic Response Characteristics And Recongnize Pattern Of The Ordovician Fractured-vuggy Reservoirs In Tazhong Shunnan Area

Deeply buried (more than6500m) and complicatedly structured, the Ordovician Carbonate reservoirs in Tazhong Shunnan area are difficult to recognize and characterize. In this paper, I first used stochastic medium to precisely describe fractured and porous reservoirs with muti-scale under the constraint of3-D seismic data, drilling data and logging data of this area. Then we studied the factors affecting seismic response patterns of porous reservoirs by forward modeling techniques based on non-homogeneous medium wave equation. In this process, we mainly considered features of porous reservoirs (e.g. the scale and density of fractures, the fluids contained, etc.), as well as the attenuation of sand layers on the surface. In the end, we optimized the attributes most sensitive to porous reservoirs, which can help to provide a foundation for effective recognition of reflection characteristics in different strata and to reduce multiple solutions for reservoir prediction.The main contents and results of this paper are carried out as follows:1) Rock physics research was conducted in target area to obtain related parameters for model construction, elastic inversion, fluid identification and reservoir prediction.2) A direction factor,θ was introduced to a new expression of vector autocorrelation function, which could provide the random medium certain advantages on direction. Then we finely described the fractured and porous reservoirs with their long axis,l, short axis, s, and density, P. These parameters were calculated by intercept method.3) The theory of detectable resolution of small-scale fractures was improved by studying the relationship between the fractures’width and the amplitude factors in different case. Results show that on migration profiles, the lateral recognizable limit is one fourth wavelength of the surrounding rocks, and when Rl≥Rs (R, is reflection coefficient of fractures and Rs is background reflection coefficient), the longitudinal recognizable limit is hmind. In addition, the method of calculating vertical and horizontal scale was given, which provided the basis for evaluating the size of vuggy reservoir in actual data.4) A correspondence between fractured reservoirs (geological) and seismic response (geophysics) was established based on the research of affecting factors including reservoirs’ characters (scale, angle, density and fluid), data acquisition, data process, image and attenuation of sand layers on the surface.5) The Ordovician fractured reservoir models in Tazhong Shunnan area were built in different strata. Meanwhile, seismic response patterns in this area were concluded based on the research to field data and theoretical data.6) Some attributes with a clear geological meaning and sensitive to vuggy reservoir were optimized. A complete set of technical sequence for reservoir prediction in Tazhong, Shunnan area was constructed including the process of vuggy reservoir modeling, forward modeling in inhomogeneous media, seismic wave field analysis, seismic attributes optimization, etc. Based on this technical work flow, the characteristics of seismic wave field and seismic response pattern were summarized several fixed patterns. These patterns were highly consistent with actual data collected in a later time. Further, three favorable exploration target area were selected thought this analysis, which represent that an effective prediction of fractured reservoir was achieved.The main innovations of this paper are detailed as follows:1) A new expression of vector autocorrelation function was derived by introducing direction factor,θ. This expression can help to more finely descript geological models of Ordovician fractured reservoir.2) A correspondence between fractured reservoirs (geological) and seismic response (geophysics) was established based on the research of affecting factors including reservoirs’ characters (scale, angle, density and fluid), data acquisition, data process, image and attenuation of sand layers on the surface, which could guide the understanding of actual vuggy reservoir characteristics when under no constraints from well data.3) A complete set of technical sequence for reservoir prediction in Tazhong, Shunnan area was constructed. Based on this technical work flow, the characteristics of seismic wave field and seismic response pattern were summarized several fixed patterns. These patterns were highly consistent with actual data collected in a later time.