"Utilizing Decline Curve Analysis to Determine Original Gas and Oil in Place" Presented by Dr. Jeffrey Callard, Associate Professor, The University of Oklahoma Abstract The concept of radius of investigation (Ri) or distance of investigation (Di) for linear flow is utilized to determine drainage area. When multiphase flow occurs, difficulty arises in the determination of representative values of viscosity and compressibility terms used in the distance calculation. This difficulty has been overcome by back calculating the lumped fluid properties (viscosity compressibility product) from simulation runs and correlating the lumped parameter with two measures of volatility that can be obtained from field production data – Gas Oil Ratio and reduced temperature as determined from fluid gravities and reservoir temperature. The lumped fluid terms are correlated using a neural network. Decline curves can then be used to identify the distance of investigation at the transition of infinite acting linear flow and boundary dominated flow and the boundary dominated data can be used to determine estimated ultimate recovery. By determining both the ultimate recovery and the in place hydrocarbons the recovery factor can be resolved preventing gross errors in reserve determination by decline curve methods only. Biography Dr. Callard is a professor at OU specializing in Production Analysis.