Fault rock petrophysical properties

Fault seal prediction in hydrocarbon reservoirs requires an understanding of fault seal mechanisms, fault rock petrophysical properties, the spatial distribution of seals, and seal stability. The properties and evolution of seals within fault zones can be evaluated using the combined results of structural core logging, microstmctural and physical property characterisation, together with information on fault populations from seismic and outcrop studies and well test data. 

Successful seal analyses depends upon the amalgamation of data from the miero-scale to the macro-scale. This review demonstrates that improvements in fault seal risk evaluation are possible. The future direetions for improving fault seal risk evaluation are also discussed. The most critical of these are characterisation of the internal structure of fault zones, generation of a database for fault rock petrophysical properties and incorporation of the impact of realistic fault zone geometries into reservoir modelling programs. 

Fundamental to a successful fault seal analysis is quantification of the petrophysical properties of the different fault rocks present in the hydrocarbon field under investigation. The critical properties which require quantification are permeabilities, capillary entry pressures, transmissibility, fault-rock thickness and the strength of the fault rocks. One of the reasons why fault seal analysis and reservoir modelling has proved difficult has been the absence of data on these properties. Analysis of the petrophysical properties of... 

Fig. 18. Reviews of the critical factors needed for an integrated seai analysis. These include (i) data on the 3D sediment architecture (ii) the petrophysical properties of the fault rocks present (iii) the architecture of individual fault zones and (iv) the fault array evolution.

The analysis presented in the paper has highlighted the need to integrate data sets from different scales into a seal analysis (e.g., Leveille et al., 1996). Fig. 18 reviews the four critical factors needed from the different scales. These include (i) data on the 3D sediment architecture (ii) the petrophysical properties of the fault rocks present (iii) the architecture of individual fault zones and (iv) the fault array evolution. It is the combined resolution and characterisation level of each of these which defines the risk level of the seal analysis. There is an important geohistory component in each of these factors. This emphasises the problems associated with transferring data or results from areas with different geohistories, with-out consideration of the different geohistories involved. 

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