Sealing potential

In many cases faults will only restrict fluid flow, or they may be open i.e. non-sealing. Despite considerable efforts to predict the probability of fault sealing potential, a reliable method to do so has not yet emerged. Fault seal modelling is further complicated by the fact that some faults may leak fluids or pressures at a very small rate, thus effectively acting as seal on a production time scale of only a couple of years. As a result, the simulation of reservoir behaviour in densely faulted fields is difficult and predictions should be regarded as crude approximations only. 

In high pressure sealing in the oil field service, it should be noted that hardness, modulus, extrusion resistance and resistance to blistering under rapid decompression can all be increased with an improvement in cross link density. However the elongation is reduced, the elasticity diminished and so the sealing potential is lessened. 

Agitated stirred tanks are preferred when high gas-liquid interfacial area is needed. Disadvantages include maintenance of the motor and seals, potential for contamination in biological and food applications, and higher cost. 

The evaluation of fault-seal potential along individual faults can be time consuming if each fault has to be mapped in enough detail to allow accurate definition of reservoir and fault intersections. It is often more efficient to divide the evaluation process into two phases ... 

These rapid variations in fault rock content and, particularly, in the content of potentially sealing lithologies raise the question of whether or not deterministic predictions of fault seal potential are feasible. Sandstone derived breccias within the fault zones shown in Figs. 3, 6 and 7 occur either as thin sheets of limited extent or as localised lenses. This patchy... 

Diagenetic analysis has proved to be useful in order to constrain the depths at which faulting occurs, and may help to predict deformation mechanisms and the related fault characteristics. The diagenetic processes are also important after the faults have been generated, as modifications of fault structures may occur during deeper burial. Understanding the deformation mechanisms is important in order to perform valid evaluations of the sealing potential of faults in reservoirs. 

The eastern area of Block 30/9 is structurally not as well constrained as the western area because of the seismic data quality. In addition, the hydrocarbons are located in geologically more heterogeneous reservoir units (channels). Consequently, the sealing evaluation performed is more uncertain, and should be used as a guideline rather than an exact measure of the sealing potential. The reservoir is thinner and less shaly, and if sealing is to occur then cataclasis and/or diagenesis would have to play a more important role. The lowest values of SGR are found on the lower parts of the faults (Lower Ness Fm). 

A proper understanding of the above items, including maturation and filling history, formation pressure distributions, intra-reservoir communications, fault and top seal potentials, and leakage mechanisms, is considered essential for resource assessment, safe drilling of further explora-tion/delineation and production wells, and for reservoir management and production planning of the Njord Field. 

Hippler, S. j. 1997. Microstructures and Diagenesis in North Sea Fault Zones, Implications for Fault-Seal Potential and Fault-Migration Rates. In Surdam, R. C. (ed.) Seals, Traps and the Petroleum System. American Association of Petroleum Geologists Memoir, 67, 85-101. 

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