| Description |
The theories for least squares interferometric datuming from vertical seismic profile (VSP) to horizontal single well profile (SWP), the least squares interferometric VSP to surface seismic profile (SSP) transform and interferometric prediction and subtraction of surface waves are presented and applied to synthetic and field data. Unlike the conventional datuming methods, which cannot eliminate the reflections that originate from the structures above the datuming line, the least squares interferometric datuming technique can provide a datumed result that only contains reflections from below the new datum line. The least squares interferometric VSP to SSP transform not only can attenuate the multiples and crosstalk artifacts but also mitigate the artifacts caused by the finite aperture limits of the acquisition geometry. The interferometric surface wave attenuation technique can remove surface waves completely while preserving the useful reflections. There are three main chapters in this dissertation. In Chapter 2, the SWP to VSP datuming equation is derived for a two-state model and the inversion problem is solved by a conjugate gradient algorithm. In theory, the datuming equation eliminates all surface-related multiples in the data. Numerical tests are applied on synthetic data and field data, which shows that least squares interferometric datuming largely removes the reflections from structures above the datuming line and the crosstalk artifacts. This technique requires an up-down going wavefield separation. In Chapter 3, the SSP to VSP transform is derived for a two-state model and the inversion problem is solved by a conjugate gradient algorithm. The equations can be used to give an SSP data set without free surface-related multiples. The up-going and down-going wavefields in the VSP data are separated at the receiver side and the least squares interferometric transform technique is applied to the up-going and down-going wavefields separately. A matching filter correction scheme is used to attenuate the artifacts caused by the limitations of the acquisition geometry and the nonsurface-related multiples. Both synthetic data tests and field data tests show promising results. In Chapter 4, it is sometimes difficult to eliminate surface waves by traditional filtering approaches, such as an f - k filter, without damaging the primary reflections. As a partial remedy, I propose an interferometric method to predict and subtract surface waves in seismic data. The removal of surface waves by the proposed interferometric method consists of three steps: (1) remove most of the surface waves by a nonlinear local filter; (2) predict the residual surface waves by the interferometric method; (3) separate the residual surface waves from the result of step 2 by a nonlinear local filter and remove the residual surface waves by a matched filter from the result of step 1. Field data tests, both for two-dimensional (2D) and three-dimensional (3D) data, show that the method effectively suppresses surface waves and preserves the reflection information. |
