Zhang, Sihai (China University of Petroleum) | Li, Xiang Yang (China University of Petroleum) | Dai, Hengchang (British Geological Survey) | Li, Xiaoming (China University of Petroleum) | Yin, Zhiheng (China University of Petroleum)
The C-wave imaging may be degraded by the diodic effect introduced by the gas cloud though C-waves have been commonly used to image through gas cloud. This diodic effect may be compensated with a velocity perturbation method which decouples the diodic moveout into two parts: the base velocity and the velocity perturbation. In this paper, the velocity perturbation is written with base velocity and the PS velocity of positive and negative offset. And the relation between velocity perturbation and gas reservoir is discussed. A land 2D3C seismic dataset is analyzed from the Sanhu area in the Qaidam basin, northwest China and significant diodic effects are observed in the data. The perturbation approach is applied to this data and the resultant C-wave imaging and the details of the reservoir structure are significantly improved. The characterization of the reservoir boundary using velocity perturbation is well consistent with the real reservoir.
Dai, Hengchang (British Geological Survey) | Li, Xiang Yang (British Geological Survey) | Ford, Richard (Imperil College London) | Yu, Chenye (PetroChina Daqing Oilfield Limited) | Wang, Jianmin (CNPC Daqing Geophysical Exploration)
We performed a case study to use PS converted waves for fracture detection for a 3D land dataset. In this study, the azimuthal variation of NMO velocity of PS converted waves is used to detect the fracture properties. The direction of maximum velocity indicates the fracture direction and the velocity perturbation indicates the anisotropy. The stack image when compensated for azimuthal velocity variation showed enhancements in terms of reflection and fault definition. The mapped distribution of the direction of maximum velocity and the velocity perturbation outlined the fracture system of the reservoir and showed a clear trend between the direction of maximum velocity and the Daqing anticline location.
We present a practical approach to perform 3D pre-stack Kirchhoff time migration in a PC cluster and to build the migration velocity model. This approach is successfully applied to a 3D-4C OBC dataset acquired in the North Sea to use its PS-waves to image the structure under a gas chimney. The results show that neither VTI nor HTI anisotropy can be observed in this dataset. An isotropic, Common Image Point (CIP)-consistent velocity model is sufficient for imaging processing. The 3D migrated results are encouraging. The structure under the gas chimney is clearly imaged using PS-waves. The faults in the target area can be clearly identified. These structures are confirmed by the drilling results.
This paper reviews the recent developments in converted-wave (
Liu, Enru (Edinburgh Anisotropy Project) | Queen, John H. (Conoco Inc.) | Li, Xiang Yang (Edinburgh Anisotropy Project) | Chapman, Mark (Edinburgh Anisotropy Project) | Chesnokov, Evgeni M. (U. of Oklahoma) | Lynn, Heloise B. (Lynn Inc.)