Pickett's plot method to estimate height above free-water table in oil reservoir

Abstract

The free water table is located at the base of a hydrocarbon column and the transition zone. The free water table indicatess the fluid contacts which are critical for field reserve estimates and field development. Estimation of free water table usually using capillary pressure versus water saturation graph from SCAL data, but in this case, the free water level is estimated by logging data with Pickett's plot method. This technique uses petrophysical parameters on the log-log graph of porosity versus resistivity to determine reservoir characterization; one of this is the height above the free water table. The advantages of this method are low cost, accurate in simple lithologies, and unreliable in complex lithologies or low resistivity sands.The Pickett's plot method is determined by predicting petrophysical parameters (a, m, n) and formation water resistivity (Rw) first. Next, the determination of straight-line water saturation (Sw), permeability (k), capillary pressure (Pc), and height above the free water table (h). The study takes data from 2 wells (Y-1 and Y-2 ) on the Petro field Pematang formation. From the calculation, the height above free water table of Well Y-1 upper formation is about 88.5-1150.4 m, and lower formation is about 159.3 – 973.5 m, Well Y-2 is about 265.5 – 1327.4 m.