A method for recovery of reflection amplitude in dipole acoustic reflection imaging
Wu Hongliang1, Liu Peng1, Wang Kewen1, Xiao Chengwen2, Feng Zhou1, Xin Yi2, Duan Wenxing2, Li Yusheng1
1. PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China;
2. Exploration and Development Research Institute, PetroChina Tarim Oilfield Company, Xinjiang Korla 841000, China
The dipole acoustic reflection imaging technology can detect the geological structures such as fractures or caves within tens of meters outside the well, which is of great significance for oil and gas exploration and development. Considering that energy attenuation occurs during the propagation of shear wave in strata, which results in the low reflection amplitude on a long propagation path, and the poor imaging quality of the corresponding long-distance reflector outside the well, a set of methods for recovering reflection amplitude can be introduced to solve above problems. These methods mainly include two parts:(1) improving the formula of energy compensation for wavefront diffusion as considering the influential factors such as logging environment and calculation unit, and further using it to recover the loss energy caused by diffusion of the reflected shear waves in strata; (2) establishing a formula of prestack inverse Q filtering applicable for processing logging data, and applying it to calculate the inelastic attenuation of strata for compensating the reflected waves on the basis of increasing the constraints of low-frequency and high-frequency limits of amplitude compensation. Obtaining the accurate quality factor Q of shear wave is the key to successfully implement the prestack inverse Q filtering method. To this end, this paper proposes a method to calculate Q jointly using the dipole direct shear waves measured and numerically simulated. This method focuses on correcting the attenuation value for geometric diffusion under the measured amplitude of direct waves by the numerically simulated direct waves. Finally, the feasibility and effectiveness of this set of methods for compensating for the amplitude of dipole shear wave are verified by the processing and analyses of on-site examples.
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2020, Vol. 41 
