Quantification of Fracture Systems Using Fourier Analysis

Abstract

Abstract

Fractures are a response to stress and as such represent strain within the rock. There are many ways to calculate strain but most of the systems require the assumptions of penetrative strain where the entire rock body reacts to the deformation process. In the case of fractures, the strain is discrete and does not meet the tradition methods of measuring strain energy. Fractures are typically measured with a scan line and the results create a comb function where the value of the function is set to zero (no fractures present) or one (fractures are present). This can easily be modified by a feature of the fracture (height, resistivity response, or a myriad of other features). With a series of smoothing curves a fracture response can be turned into a waveform and as such can be analysed for dominant frequency (spatial) and relative fracture intensity.

A series of outcrop measurements taking from UAV flights in the Wind River Basin of central Wyoming and analysed with Fourier Analysis reveal the natural fracture systems do not effectively connect vertically but rather appear to have better lateral connection. Using Fourier analysis different stratigraphic layers can be compared and the relationship between vertical fluid migration to horizontal migration can be determined. This observation has implications to regional fluid migration within Foreland Basins and the development of regional unconventional traps.

The advantages of series analysis in fractures systems is that it gives the opportunity to look at fractures as a system rather than as isolated events and also allows the comparison of layers or wells so that fracture fairways can be recognized. Images of a series of outcrops were acquired through the use of a UAV. The analysis from this work show that the fundamental anisotropy of the rock (bedding) creates fracture barriers that could influence the behaviour of subsurface reservoirs.

This method has also been successfully employed in estimating strain within folds, regional fluid migration patterns, and in describing unconventional petroleum systems.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018