Volcanic Rocks Containing Hydrocarbons

As explained in the article "Evaluating Volcanic Reservoirs" in the spring 2009 issue of Oilfield Review, textures and mineral composition of volcanic formations make them difficult to characterize. By combining measurements from nuclear magnetic resonance (NMR), borehole resistivity imaging, and neutron capture spectroscopy, interpreters have been able to overcome the challenges presented by volcanic reservoirs.

In a case study from a deep gas-rich reservoir formed of ejected and erupted volcanic material, PetroChina and Schlumberger engineers devised a workflow to estimate gas in place. Interpreters populated a seismic-based structural model with porosity and saturation values derived from NMR and spectroscopy logs. The resulting estimates of gas in place supported the decision to proceed with development.

An example from India highlights the importance of combining compositional and textural information in correlating volcanic layers between wells. Operating in the Cambay basin, Gujarat State Petroleum Corporation combined borehole image logs with elemental concentrations from spectroscopy logging data to understand heterogeneous Deccan basalt formations that produced oil in some wells but not in others.