Three-dimensional Calculation and Visualization of Fault Gouge Ratio

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractUnderstanding the sealing characteristics of faults is critical in assessing the hydrocarbon potential of traps formed by faults. Fault gouge ratio and juxtaposition analysis have often been limited to a single cross section (a two-dimensional approach) or to a single, isolated fault surface (a partial threedimensional approach). We have now developed a full threedimensional solution for calculating fault gouge ratio. This method uses a continually varying clay volume fraction, a network of faults (isolated, dying and/or branching), and displacement along the fault surface (instead of just the dip component). The structural model used as the framework for this calculation is based on geometric reconstruction techniques that construct faults and horizons in threedimensional space, allowing easy and rigorous calculation of juxtaposition and displacement. These last two items are necessary input to the fault gouge ratio calculation.The steps in calculating fault gouge ratio in threedimensional space are as follows: (1) create structural framework, (2) calculate volume of clay (Vcl) as a continually varying property within this structural framework, (3) determine displacement, allowing for oblique slip, and (4) calculate fault gouge ratio for hanging wall and foot wall blocks, and sum to determine the ratio for every point on the fault Rigorous calculation of fault gouge ratio depends on a robust structural model. With the model described herein, a variety of scenarios may be investigated, thus incorporating uncertainty into the calculation. Determining whether a fault will act as a seal, or whether there is potential for development of leaks during the production of the reservoir depends on many variables. Minimizing the uncertainty in this part of the analysis may provide increased confidence in assessing risk.