Best Practices for Geochemical Sampling in Shale Gas Wells
Geochemical sampling in shale gas wells is simple, inexpensive, and provides information not easily available from other technologies. Acquisition of geochemical samples also provides insurance that, even if it is not possible to log or test the well, there will be information available to help evaluate the well.
Three basic types of geochemical samples are recommended in shale gas wells: 1) wet cuttings, 2) Isojar samples of any liquid hydrocarbon shows, and 3) mud gas (Isotubes). In a thermogenic shale gas play, wet cuttings samples can be used to verify whether or not the shale of interest has sufficient total organic carbon (TOC), thickness, and thermal maturity to have generated economic amounts of gas. Analysis of liquid hydrocarbon shows caught in Isojars can provide information on hydrocarbon source and the thermal maturity level at which the hydrocarbons were generated.
Isotopic analyses on mud gas samples caught in Isotubes provide a myriad of information having multiple applications. First, mud gas isotopic analyses can verify compositional shows logged by the mud gas chromatograph. Second, mud gas isotopic analyses can also provide information regarding gas origin (thermogenic versus biogenic), variations in gas sourcing facies within the shale, and reservoir compartmentalization. Delineation of compartments and recognition of different gas isotopic signatures for the individual compartments is particularly important because this information can help determine where to perforate. It can also be used to help determine which compartments (perforations) are likely to be contributing the most gas to either frac gases or produced gases.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009