Recognizing Bell Canyon and Cherry Canyon Behind Pipe Pay Sands Reeves and Culberson Counties, Texas

The difficulties in recognizing pay versus non-pay zones in the Permian Bell Canyon and Cherry Canyon sands in Reeves and Culberson counties are the result of: 1.) the presence of residual oil, 2.) the very fine grain size (Mz = 0.05 to O.10mm), 3.) the high Rw values (Rw = 0.15 to 0.25 ohm-m) and 4.) the presence of authigenic chlorite and mixed-layered illite-smectite clays. The fine grain size and the authigenic clays result in high irreducible water saturations. These high irreducible water saturations together with the presence of residual oil in both pay and non-pay sands and high Rw values result in low resistivity contrast between pay and non-pay sands. In order to overcome these difficulties, a series of crossplots and core analysis were used to determine pay from non-pay zones in two wells. Using net pay cut-offs of Vcl < 15% (dispersed clay), effective porosity (0e > 15% for 1.0 md) and Archie water saturation (Swa) < 60%, three "behind pipe" pay zones were identified in the two wells. These three zones have a combined hydrocarbon pore-meter thickness of 1.5 (5.0 pore-feet which calculates into 1.55 million barrels of oil in place assuming 40-acre drainage."