A wide range of observations indicates that petroleum commonly migrates or leaks through thick sections of mud-rich sediments. In continental slope settings, for example, petroleum often migrates from mature source intervals to traps through several kilometres of mud dominated section. Seismic bright spots, waste zones and gas chimneys indicate the presence of petroleum in mud-rich seismic volumes and have been used to imply leakage pathways. However, whilst seismic data may indicate the presence of gas, it cannot indicate its origin. Results indicate that at a single porosity, the range of potential column heights between facies is a factor of two. Permeabilities of the facies vary by three orders of magnitude, depending on effective stress, and laminated and lenticular facies are highly anisotropic. Petroleum saturations required to breach the mudstone facies are also highly variable, ranging from < 1% to > 20%. All these numbers help us to quantify seal risk in a more quantitative way, related both to capillary breach or in the context of a permeability-constrained charge-leak model. An important conclusion is that total connected porosity for any facies is a function of lithologies ratio,while permeability and CEPc were functions of internal architecture/type of connectivity patthern typical for each facies.


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