Petroleum Geochemistry Division – Shale Gas...

Exploration and production of natural gas in Australia has, over recent years, begun to focus significantly on unconventional sources, in particular shale gas.

At Geotech, routine geochemical programs are being geared towards the analysis of shales to assess their potential as self sourcing, low permeability reservoirs.

The analytical approach taken when considering shales as a source of tight gas is based primarily on the premise that source rocks responsible for the generation of gas and liquids in these systems must also form effective seals, in order to prevent the loss of fluids from the reservoir. Gas is retained in the shale by adsorption to the organic matter or held within the pores due to ultra low permeability.

Typically, an analytical program aimed at assessing a shale gas system will involve the following:

    TOC/Rock Eval Pyrolysis
          To determine whether significant amounts of free hydrocarbons are present in           the sediments, if the shales are sufficiently mature to have generated           hydrocarbons, and the level of organic carbon as this the adsorption medium.

    Whole Extract GC-MS
          To characterise the free hydrocarbons present in the shales with regards to           source and thermal maturity.

    Oil/Gas/Source Rock Correlation
          To correlate the free hydrocarbons extracted from the shales with crude oil or           gas/condensate recovered from the underlying reservoirs.

    Mercury Injection Capillary Pressure Testing
          Intrusion testing is utilised to determine the seal capacity of the shales.

This combination of geochemistry and core analysis has also found application in the assessment of conventional seal studies.