Prediction of petrophysical characteristics from borehole gas and drilling data

Several sources of data are available at the well site during drilling operations that have potential for prediction of petrophysical characteristics. Data of particular interest include gas analyses (borehole gas), which conventionally comprises low molecular-weight hydrocarbons (C1 to C3 ± C4 and C5) but more recently may include a wide range of non-organic gases from well-site mass spectrometry, and rate of (bit) penetration (ROP) and the associated drilling exponent. (DXC, defined as R/N = A (W/B)2 where R = rate of penetration, N = revolutions per minute, A = matrix strength, W = weight on bit and B = bit diameter). Because borehole gas, ROP and DXC are available in real time, and at no extra operational expense, their amenability to prediction of petrophysical characteristics is important to establish as by using them it may be possible to produce synthetic wireline logs and/or direct estimates of porosity, saturation and permeability during drilling at the well site.