Tina Lohr

Prediction of subseismic faults and fractures: Integration of three-dimensional seismic data, three-dimensional retrodeformation, and well data on an example of deformation around an inverted fault

In addition to seismically mapped fault structures, a large number of faults below the limit of seismic resolution contribute to subsurface deformation. However, a correlation between large- and small-scale faults is difficult because of their strong variation in orientation. A workflow to analyze deformation over different scales is described here. Based on the combination of seismic interpretation, coherency analysis, geostatistical analysis, kinematic modeling, and well data analysis, we constrained the density and orientation of subseismic faults and made predictions about reactivation and opening of fractures. We interpreted faults in seismic and coherency volumes at scales between several kilometers and a few tens of meters. Three-dimensional (3-D) retrodeformation was performed on a detailed interpreted 3-D structural model to simulate strain in the hanging wall at the time of faulting, at a scale below seismic resolution. The modeling results show that (1) considerable strain is observed more than 1 km (0.62 mi) away from the fault trace and (2) deformation around the fault causes strain variations, depending on the fault morphology. This strain variation is responsible for the heterogeneous subseismic fracture distribution observed in wells. We linked the fracture density from the well data with the modeled strain magnitude and used the strain magnitude as a proxy for fracture density. With this method, we can predict the relative density of small-scale fractures in areas without well data. Furthermore, knowing the orientation of the local strain axis, we predict a fault strike and opening or reactivation of fractures during a particular deformation event.

Quantitative fracture prediction from seismic data

ABSTRACT This paper presents results obtained from an area located east of Bremen, Germany, where gas is produced from a deep Rotliegend sandstone reservoir. Faults, fractures and associated deformation bands at reservoir depth have an important influence on the productivity of the gas field as fractures are cemented and tight and may act as permeability barriers. This contribution comprises the development of new coherency tools to better image sub-seismic faults and lineaments from seismic data, and the development of fracture attributes in order to quantify fracturation and its areal distribution. The fractal behaviour of faults was used to establish a relationship between coherency processed seismic data and borehole images at log scale. The ‘fractal dimension’ (FD) of the length of a fault population can be interpreted as a characteristic parameter describing local geology in terms of fracturation. Calculating FD for each point of a seismic grid yields an areal distribution of this value. Correlating seismic-derived FD values and fracture populations derived from borehole images defined a linear relationship which can be used to forecast the distribution of sub-seismic fractures and deformation from seismic data.

Structural Architecture and Deformation Styles Derived from 3D Reflection Seismic Data in the North German Basin

The Upper Cretaceous Ilhabela sandstones, which represent the main reservoir unit in the Santos Basin, were deposited in a fluvial to shallow marine environment during a period of active basaltic volcanism. The volcanics have been partly eroded, providing the reservoir with volcanic rock fragments and causing a complex diagenetic history. This has resulted in the local occurrence of sandstones with complex lithology and elastic properties differing from the basin trend (Klarner et al, 2005). For better prediction and interpretation of the amplitudes and AVO behaviour of the Ilhabela reservoir it is essential to map the occurrence of the volcanics as well as the transport direction of their erosional products. In this paper, typical seismic features are presented which may help to identify volcanics in the Upper Cretaceous sequence.