Impact of faults on fluid flow in microbial and hydrothermal carbonates

Faults have a major impact on subsurface fluid flow, which is important to understand for a range of applications such as oil and gas exploration and production, groundwater flow, as well as CO2 storage and radioactive waste disposal. Massive advances have been made, particularly by UK based academics and service companies, developing the tools to allow the impact of faults on fluid flow to be predicted in siliciclastic sediments (i.e. sand – shale sequences). For example, we have: (i) built massive databases on the single and multi-phase flow properties of faults in siliciclastic sequence (Fisher and Knipe, 2001); (ii) developed algorithms for predicting the distribution of fault rocks along faults (Yielding et al., 2010) and, (iii) developed sophisticated software that use these data and algorithms to predict how faults impact fluid flow in the subsurface (e.g. Traptester, RDR Fault Seal Plugin for Petrel). Unfortunately, such tools have not been developed for carbonate reservoirs, which contain most of the worlds remaining conventional petroleum resources and a large proportion of our unconventional petroleum (note that many shale gas plays are mainly composed of carbonates). To fill in this knowledge gap, a partnership between the University of Leeds and Badley Geoscience has been established to build a database of the properties of faults in carbonates and to develop software to use these data to predict the impact of faults on fluid flow in carbonate reservoirs. The project is currently progressing well in that we have already conducted extensive studies of faults within the chalk and Zechstein reservoirs in Europe as well as limestones from Europe, Middle East and the USA. A key gap in our knowledge and data is the impact of faults on fluid flow in microbial and hydrothermal carbonates. This is important because these are some of the most important reservoirs being currently explored in the sub-salt offshore South America and South West Africa.

The project will be composed of four distinct work packages (WP1-4):-
WP1 – Conducting field work to understand the structure of faults in microbial and hydrothermal carbonates, the control on the distribution of fault rock types and collect samples for laboratory analysis. Outcrops have already been identified in Italy, Turkey, and Brazil, which represent a range of tectonic environments and burial histories.

WP2 – Conduct laboratory measurements of the petrophysical properties (porosity, permeability, capillary pressure) of fault rocks collected from the field and integrate these measurements with microstructural studies (optical, CL and SEM) to identify the key controls on the flow properties of the faults.

WP3 – Conduct triaxial experiments on undeformed carbonates collected from outcrop to further understand the factors (rheology and stress) that control the formation of the different fault rocks that are identified in the field.

WP4 – Develop methodologies and/or algorithms to incorporate this data into software products that can be used to model the impact of faults on fluid flow in carbonate reservoirs.