Geochemical Analysis on Prospective Gas Shale Reservoirs at Perth Basin, Western Australia

Jafary Dargahi, Hanieh; Rezaee, Reza

The decisive link between organic geochemistry and determining shale gas reservoirs necessitates us to qualify shale layers regarding with their geochemical characteristics, besides accounting geochemical commonalities within shale reservoirs. Lucrative gas shales mostly contains up to 3% TOC along with vitrinite reflectance of more than 1.1%. Having sufficient thickness is another crucial criteria, dialectically these layers might be consists of either type II or type III kerogen. Shale thermal maturation can be identified based on measuring Tmax considering its relation with other geochemical properties such as TOC, remaining gas potential as well as Hydrogen Index (HI), the HI value in shale gas systems considered to be >350 mg HC/g rock. Geochemical parameters of various wells indicates higher TOC value in Carynginia formation compared to Kockatea shale, with mostly more than 3 wt% showing a potentially reasonable shale reservoirs. Vitrinite reflectance measurements suggest mainly type II and III kerogen for studied shale reservoirs. Van Krevelen diagram confirms kerogen types of II and III for both Kockatea and Carynginia formations. The diagram of TOC versus remaining gas potential (mg HC/g rock) implies on higher maturation in Carynginia formation. Unlike Kockatea that plotted onto the oil and gas prone area with mixed type II/III kerogen, Carynginia formation only plotted inside gas prone area with type III kerogen. Geochemical analysis on likely gas shale systems within Perth Basin (Permo-Triassic intervals) predicts the eligible gas shale potential alongside the desired organic richness, organic maturity and sufficient thickness in organic rich strata.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013