Wednesday, September 26, 2012

Importance of Temperature in Unconventional Plays

It has been observed that some of the best liquid producing areas in the Niobrara shale are associated with thermal anomalies, in both the Power River and DJ basins, the Wattenberg field, for example. Here I would like to propose a few possible reasons behind this observation. Some may be well known but some may have not been so obvious,
  1. The thermal maturity of the Niobrara is relatively low, and areas with higher geothermal gradient would have relatively higher maturity. Higher maturity provides better oil with lower viscosity that makes it easier to flow. Higher maturity also means higher GOR that helps with pressure, ie. better drive and production rate. Higher maturity increases the intra-kerogen porosity generated in the late maturity stage to help retain more oil. ... ... 
  2. Higher present day reservoir temperature also means lower viscosity - if you ever bought motor oil for your car - you understand that. Viscosity is really important in an unconventional play as it has large enough variability to counter the extreme low permeability - yes, Darcy's law still applies .
  3. Temperature may also affect a shale play by influencing interfacial tension (IFT). Lower interfacial tension can help it two ways. It can increase relative permeability, and increase oil saturation, especially in the more water wet parts of the reservoirs (silty zones). Temperature also affects contact angle between the fluids, although the effect is less well studied. 
The Eagle Ford shale does not produce well to the west toward the Mexico border. Temperature could be one of the reasons. At the same maturity, the present day temperature may be lower there compared to the eastern counties.    

Although there are many factors that go into a shale play. As we have plenty of temperature data in typical onshore basins in the US, when evaluating an area, it may be worth while to make a temperature or geo-thermal gradient map. Everything else being equal, ares of higher temperatures may be more favorable. 

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