Oil FVF (rbbl/STB) Estimation of original oil in place (STOIP) is one of the main important and influential responsibilities of reservoir engineers. This task is crucial for oil and gas operators because it allows them to keep track of how much oil/gas is still left in their prospects and to update their investors about their predictions of future gains/losses. Estimating reserves always encompasses some degree of uncertainty and it comes mainly from the lack of subsurface data such as petrophysical properties. In this continuous assessment, you need to estimate the STOIP for one of the reservoirs in the Sothern North Sea region. This oil reservoir consists of 6 layers of 200ft shaly sandstone and has the initial pressure of 4000psia, temperature of 199.4F. In addition, a series of laboratory and field data are provided in Table 1 figure 1 (oil volume factor measured at the reservoir temperature). You need to do uncertainty analysis on these data to make the best STOIP estimation from this hydrocarbon reservoir. The following steps are recommended to calculate STOIP. a) Calculate average porosity and absolute permeability of the core plug samples taken from this reservoir. b) Determine the bubble point pressure and oil formation volume factor at reservoir condition for STOIP calculation. c) Estimate original oil in-place (STOIP) for this hydrocarbon reservoir considering volumetric behaviour. Please take into account the uncertainty coming from subsurface data and do proper sensitivity analysis (e.g. Monte Carlo simulation) to justify your results. Assume reservoir has a square shape with an area of 500 acres. Table 1: Petrophysical properties of the oil zone from well log interpretation Depth, feet Porosity Permeability (mD) Clay Volume Swi 4000 0.28 48 0.27 0.21 4200 0.24 43 0.33 0.28 4400 0.13 22 0.25 0.19 4600 0.18 31 0.41 0.25 4800 0.33 84 0.11 0.27 5000 0.28 51 0.21 0.22 5200 0.27 49 0.23 0.25 1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00 0 1000 2000 3000 Pressure (psig) 4000 5000 6000 Figure 1. Measured oil volume factor at reservoir temperature.