Estimation of fracture parameters from P-wave AVOA data based on equivalent media theory
(2.Hubei Subsurface Multi-scale Imaging Key Laboratory, Wuhan, Hubei, China 430074)
(3.Research Institute of Exploration and Development, Northwest Oilfield Branch Co., SINOPEC, Urumqi, Xinjiang, China 830011)
【Abstract】The contrasts of the fracture weakness may be positive or negative while the fracture weakness is nonnegative. Layer stripping is normally used to invert the fracture parameters of individual layers in sections. Otherwise, the upper layer of each interface is assumed to be isotropic to simplify inversion algorithms. Large errors in the final estimations of the fracture parameters may be introduced by layer stripping or inversion methods assuming that upper layer of each interface is isotropic. Thus, we propose in this paper a method for estimation of fracture parameters from P-wave AVOA data based on equivalent media theory. We express the contrasts of the fracture weakness as multiplication of the first-order difference matrix with the fracture weakness itself, and express the reflected amplitude as a function of the fracture weakness, which can be used to estimate normal and tangential weakness. A priori information about the model can be added to the objective function as penalty term according to Bayesian theory. The AVOA inversion results for a synthetic model show that the fracture weakness can be reliably estimated. Fracture weakness and fracture density are estimated from real seismic data in Makit area in the Tarim Basin. The AVOA inversion results are consistent with well and logging information, which means they can be used to determine fractured reservoir locations.
【Keywords】 equivalent media theory for fractures; fracture weakness; fracture density; P-wave AVOA;
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