Geochemical, geological, and petrophysical evaluation of Garau Formation in Lurestan basin (west of Iran) as a shale gas prospect

Abstract

The Garau Formation in western Iran is a potential shale gas play. To evaluate its gas potential, a geochemical, geological, and petrophysical study was conducted on samples from the Baba Ghir 1 well drilled in Lurestan District (W Iran). Organic matter analysis of Garau Formation shows that total organic carbon (TOC) ranges between 0.42 and 2.43 wt% and this formation possesses kerogen type III with a high degree of maturity, reflecting gas window conditions. Mineralogical analyses show that the lithology of Garau Formation in this well is carbonate-dominated and the clay mineral content is less than 4%, and displays several characteristics that are similar to the Eagle Ford shale. Based on the relationship among quartz, carbonate, and clay minerals, the brittleness index is about 25%, a value of importance to select the best stimulation fluid. Petrophysical evaluation shows a porosity of about 5–15%. Estimation of the amount of free gas reserves possesses a good correlation with the reserves that were estimated based on petrophysical interpretation. Because of absence of underground contour maps, calculation of adsorbed gas volumes was not possible but estimates of gas storage capacity (GC) shows an increase with depth. All data indicate that the Garau Formation can be considered as a promising gas shale play.