Publications

Geomechanics is an important parameter in determining a prospective shale gas interval’s potential. The mineralogy (silica, feldspar, carbonate, and clay) and organic matter are elements that affect the geomechanical properties, which later lead to a fracturability number (brittleness index, BI) of the shale. Any shale gas exploration will benefit if the relation between the depositional process, which delivers a resultant mineralogy, and the fracturability is well known. This paper integrates the result of lithofacies and depositional environment analysis with mineralogical effect on the rock fracturability of shale and other fine-grained sedimentary rocks. Samples were taken from cores representing the Eocene section of the Nanggulan Formation in Kulon Progo, Yogyakarta. Evaluated sections were deposited as in estuary to shallow marine environments. The estuary environment is divided into the Upper Flow Regime (UFR) Sand Flat and Tidal Flat. The UFR Sand Flat environment consists of flaser-wavy sandstone domination and interbedded lenticular mudstone. The Tidal Flat environment is composed of mudstone facies in the lower part and sandstone facies in the upper part. Above these,, the depositional environment changes to shallow marine with the domination of massive mudstone facies, sandstone facies, and increasing carbonate facies. Shale samples were taken from the mudstone facies. X-Ray Diffraction data show that the variability of the mineralogical composition of estuary shale is higher than the shallow marine shale. With similar TOC numbers, the BI of estuary shale will be varied compared with shallow marine shale. However, shallow marine shales tend to have a higher fracturability. Keywords: Estuary, Shallow marine, Brittleness Index, Eocene Nanggulan Shale.