Chung-Chi Shih

Forward modeling attribute analysis for AVO and prestack depth migration

The attributes generated from forward modeling provide important information for acquisition design. Evaluating these attributes, such as amplitude, hit count, incident angles and others, can determine better shooting geometries. Because we illuminate the reflector by implementing wavefront construction based on multivalued, two-point raytracing, we are able to provide the raypath information for all receivers. The construction of the wavefront and raypath generates attributes for both the recording and the target horizon. Among these attributes, the aperture length is important for prestack depth migration and the incident angle is important for AVO analysis. These attributes combined with density information can be used to quantify the sensitivity of AVO to uncertainties in the rock properties (Sengupta and Rai,1998). Acquisition design based on common reflection stack (Chang et al., 2001) is an efficient way to optimize the shooting geometry. However, it will not provide good quality seismic data unless extra attributes are incorporated. In this paper, we will focus on attribute analysis for offset design, which is important for both AVO analysis and prestack depth migration. A synthetic model is used to present the concept of forward modeling illumination and our techniques are demonstrated on a realistic and complex salt model from the Gulf of Mexico.

Controlled stacking for improved quality of prestack depth‐migration results

Depth migration of seismic data is becoming more routine for imaging of complex geological structures. However, in some cases, the quality of the resulting depth section is lower than expected. A typical case is in imaging of salt bodies. The seismic images of steeply dipping salt flanks are frequently broken, smeared, and difficult to interpret. The study presented in this paper demonstrates one source of this imaging problem, and suggests a solution we call controlled stacking. The core of the solution is the correct muting of partial images produced by prestack depth migration (preSDM) before sorting and stacking to obtain the final depth section.

On Accurate Imaging of Steep Salt Flanks

The accurate imaging of steep flanks of salt domes has long been a challenging problem for exploration geophysicists. The problem continues to be relevant today as more and more salt domes are being shot with 3D seismic in order to exploit remaining hydrocarbon reserves. Unfortunately, the seismic images of steep salt flanks are often not satisfactory; they are either broken or appear as smeared events. Interpretation of the salt body in these cases is difficult and somewhat confusing (see figure la).