Cataclasite of a carbonate thrust fault zone of the Xerovouni Range, Epirus, Greece Impact on migration?
When hydrocarbons and fault rocks have a little chat, what do they say?
Paetoro and fault seal
Paetoro's experience in fault seal has extended over a long period, from early work on sub-regional studies of Haltenbanken Norway, to more widespread application for particular prospects - mainly in the North Sea, but also in SE Europe and Trinidad. More recently PAETORO has been working with a client onshore North Africa, using the FaultRisk software provided by Fault Seal Pty. Ltd. (Sydney) and SHSgeo (Titus Murray).
Fault seal is invariably affected by a number of complex parameters, but fault seal analysis serves to understand which ones are most important, even if uncertainty remains.
You don't have to obtain the exact answer to progress risk assessment
A criticism of fault modelling is sometimes that there is just so many variables involved, you can never really be sure of the right answer.
That is an issue, but it isn't the end of the road. Sometimes the value of an exercise is not just in obtaining the right answer, but seeing the effect of different sensitivities. A modelling exercise can help to understand which processes and variables are most critical, and shine a torch on the areas needing further attention.
There are three key types of fault seal condition - the first is juxtaposition seal, where the seal is provided by entire lithological layers juxtaposed at a fault. This type of seal can be estimated from a good understanding of fault geometries, nearby stratigraphy, and calibrating well data indications of seal, and applied in an exploration context to undrilled areas.
The second type is seal provided by the fault rock itself - this is harder to get right as there are many possible mechanisms (cataclasis, shale entrainment, cements) and the sealing faults are directly sampled only very rarely. Yet it is possible to model end members for different processes in this situation to estimate what might be possible.
Thirdly, seal can be destroyed by activity on the fault due to tectonism, or changes in the stress field affecting fault zone fractures. This requires an understanding of stress conditions now and in the past.
Juxtaposition analysis is the simplest of these processes, and is the best one to start with. If it can satisfactorily explain observed HC occurrences, then there is little need to get more complicated. If this occurs, it radically empowers exploration in stacked reservoir-seal sequences. It does require a good understanding of sealing stratigraphy and QC'ed fault geometries to do right - something that is not always done optimally utilising all the calibrating data.
If after all efforts to match hydrocarbon occurrences with reality, there still exists a mismatch to observations, then the other processes can be more fully considered. Sometimes the issue can lie totally outside fault seal - for example in charge volume and timing issues. In such instances, PAETORO is well placed with 1D basin modelling software to help investigate.
The FaultRisk software PAETORO uses in conjunction with SHSgeo and Fault Seal Pty. Ltd., is well suited to quickly address the assessment of juxtaposition and shale entrainment (SGR, or shale-gouge-ratio) fault seals. PAETORO's experience with basins of all types and structures around the world, means we are well placed to tackle the matter sensibly, should things prove to be more complicated than just juxtaposition & shale entrainment .