Estimation of Formation Porosity in Carbonates Using Mechanical Specific Energy Calculated from Drilling Parameters

A novel technique to predict porosity from mechanical specific energy (MSE), as measured using a downhole drilling dynamics tool, is proposed. The method is based on the fundamental conservation of energy principle and uses rock physics to establish a relationship between the drillability of a rock, its lithological properties, and its porosity. This new technique is particularly useful for formation evaluation of carbonate reef reservoirs drilled using the pressurized mud cap drilling (PMCD) technique. Under these conditions, the near-wellbore formation is often deeply invaded by drilling fluids and cuttings, which make interpretation of conventional logs unreliable and difficult. Since drilling measurements are relatively unaffected by this invasion, porosity determinations from MSE can provide a valuable supplement to conventional logging suites.