Prior Analysis in Determination of TI Anisotropy Type through Well-Based Modelling: A Case Study on the Deep Water Environment

Abstract

The existence of anisotropy phenomena in the subsurface will affect the image quality of seismic data. Hence a prior knowledge of the type of anisotropy is quite essential, especially when dealing with deep water targets. The preliminary result of the anisotropy of the well-based modelling in deep water exploration and development is discussed in this study. Anisotropy types are modelled for Vertical Transverse Isotropy (VTI) and Horizontal Transverse Isotropy (HTI) based on Thomsen Parameters of ε and γ. The parameters are obtained from DSI Logging paired with reference δ value for modelling. Three initial conditions are then analysed. The first assumption is isotropic, in which the P-Wave Velocity, S-Wave Velocity, and Density Log modelled at their in-situ condition. The second and third assumptions are anisotropy models that are VTI and HTI. In terms of HTI, the result shows that the model of CDP Gather in the offset domain has a weak distortion in Amplitude Variation with Azimuth (AVAz). However, another finding shows a relatively strong hockey effect in far offset, which indicates that the target level is a VTI dominated type. It is supported by the geomechanical analysis result in which vertical stress acts as the maximum principal axis while horizontal stress is close to isotropic one. To sum up, this prior anisotropy knowledge obtained based on this study could guide the efficiency guidance in exploring the deep water environment.

Saturated Fluid Variation Effect on Seismic Anisotropy: A Case Study of Deep-Water Reservoir

“…Seismic gather shows a clear hockey stick curving on the far offset which is a proof of subsurface anisotropic condition. Previous studies indicate that the anisotropy character of Sadewa Field could be categorized as VTI dominated [8] and the anisotropy degree falls into weak to medium anisotropy from Ultrasonic Core Measurement [9]. While the anisotropy measurement at such high resolution couldn't be directly incorporated to the analysis in seismic resolution [10], it brings an undeniable proof that the rock within subsurface contains anisotropy quality.…”