The determination of the gas content of shales is difficult. Empirical relationships relating the gas content to the total organic content (TOC) are tenuous. Sigra can provide an exploration system that is an advance on the normal mud logging system in that it is reliably quantitative. This system is particularly suited to obtaining the gas content of thick gas bearing formations. The system originally called gas content without coring is now know and gas content while drilling. It involves drilling in overbalanced mode, so that gas does not come from the formation. All that comes up with the drilling fluid is what goes down the hole plus the cuttings and fluids released from them. Gas is desorbed from the cuttings as they travel to surface in the hole annulus. A rotary seal at surface diverts the fluids through a cyclonic separator. The gas release is directly measured and then the cuttings gathered from the shaker are collected and further desorbed.

Fig 1 9
Figure 1. Schematic of the open hole drilling gas content measurement process.