Step 3: Resistivity Logs ILD (deep) Where do the resistivity logs give different values? This indicates where the fluids in the rocks differ from the drilling fluid In this case, it confirms the gas zone Caliper MSFL NPHI Gamma Ray SFL RHOB) Shale Siltstone Gas Formation Fluid different from Drilling Fluid Sandstone Formation Fluid similar to Drilling Fluid SLIDE 13 Now we interpret the resistivity logs For the bottom of the thick sand and the deeper sand, the medium and deep resistivity have similar values That indicates that the drilling fluid is the same as the formation fluid If the drilling fluid was an oil-based mud, then we have oil zones If the drilling fluid was an water-based mud, then we have wet sands (pores filled with water) There is a lot more that a log analyst can do – this is basic stuff that any geoscientist should be able to do Water or Oil Water or Oil Siltstone Sandstone Water or Oil Shale Sandstone Courtesy of ExxonMobil L 4 - Well Log Data