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The common practice in the oil industry is to make source rock maturity maps in terms of vitrinite reflectance (%Ro). However, vitrinite reflectance does not actually tell us to what degree the source rock has converted its generation potential to hydrocarbons. VR is merely a thermal stress (the combined effects of temperature and time) indicator, and a very poor one at that. To know how much of the kerogen has converted to hydrocarbons we not only need to know thermal stress, but also the kinetic behavior of the source rock, which depends on the organo-facies (Pepper and Corvi, 1995).     This figure shows the fractional conversion (transformation ratio) of kerogen of different organo facies as a function of vitrinite reflectance (thermal stress). We see at 0.8%Ro, each of the standard kerogen facies has experienced very different degree of conversion, 70%, 60%, 40%, 20% and 0% respectively.  Vitrinite Ro measurements are also not reliable and affected by many things, in...

The description of a forthcoming specialist conference on basin modeling includes the text: " BPSM (Basin and Petroleum System Modeling) has become an indispensable tool in frontier basins to identify risk, reduce uncertainty, and identify new potential areas. This technology has become more important over time as a result of increased understanding of processes and the rapid development of computing power. Both the hardware and the software are evolving to quantify more complex processes" One could only assess the veracity of the first part of this statement by carrying out a survey of companies to see how many use basin modeling as part of their evaluation process and how many consider it " indispensable ".  What I think can be said is that, if basin models are  " identifying risk and reducing uncertainty",  then that isn't showing up in explo ration success rates. Industry surveys show that frontier basin success rates have not changed much over th...

In an earlier post , I argued that there may be significant lateral migration within shale reservoirs that can lead to higher maturity fluids produced from lower maturity areas, and even  occasionally   dry gas production in the oil window. In this post, I would like to propose that shale reservoirs also need seals to work.  Sedimentary rocks have a wide range of pore sizes. In a conventional reservoir, HC saturatio n builds up due to higher capillary pressure caused by the buoyancy of the column (Schowalter, 1979). Saturation is highest at the crest of the reservoir.  In a shale reservoir, there may not be an effective column. The increase in saturation and capillary pressure is caused by generation of hydrocarbons. However, it will also require the presence of tight rock facies (above, below and laterally) to prevent migration out of the shale due to the increased capillary pressure. From MICP studies on shales, we see that  shales have a wide range of displac...

At a recent industry conference a poster summarised aspects of the petroleum systems in a particular basin. The authors noted that some reservoirs contained "dry gas" while others contained "wet gas". The boundary between the two was not defined but it was clear from the context that the distinction reflected the condensate content: gases having more than about 20 bbls/MMscf  of condensate were classified as "wet". Wet vs. dry gas definitions and terminology can be confusing so I thought it might be worth posting a summary here. Firstly, let's look at the composition of a typical gas condensate: This one is from the textbook on the phase behaviour of reservoir fluids by Pedersen and Christensen (2007) . We can define four groups of compounds: Methane (C1) being the only member of the first group then ethane (C2), propane (C3) and the butanes (normal and iso) making up the remaining "permanent" gases, the "condensate" range with comp...

There are currently contrasting views on the way strain is distributed within the lithosphere during rifting and the formation of passive continental margins, with direct implications for the subsidence and heat flow histories of the overlying sedimentary basins, and potentially also for the timing and degree of source rock maturity in these systems. According to some authors, the asymmetry observed between most conjugate margin pairs (e.g. West Iberia-Newfoundland, East Coast USA-NW Africa, NE Brazil-West Africa and the Southern Australia-Antarctica) results from the activity of low-angle normal faults (detachments), which shift the region of pervasive upper crustal thinning and normal faulting (lower plate) from that of intense lower crust and mantle lithosphere thinning (upper plate; see Rosenbaum et al., 2008 and references therein). A paradoxical observation, nevertheless, is that in most margins the extension measured from normal fault throws appears to be much smaller than that...