ASQUITH, G. B., M. D. THOMERSON, and M. D. ARNOLD, Texas Tech University, Lubbock, TX

ABSTRACT: Recognizing Bell Canyon and Cherry Canyon "Behind Pipe" Pay Sands

The difficulties recognizing pay vs. nonpay zones in the Permian Bell Canyon sands in Reeves and Culberson counties are the result of (1) the presence of residual oil, (2) the very fine grain size (Mz = 0.05-0.10 mm), (3) the high Rw values (Rw = 0.15-0.25), 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.

A series of crossplots was used to determine pay from non-pay zones in two wells. These crossplots include (1) Q-plot, (2) Rt porosity vs. total porosity, (3) Pickett, (4) Sw (Archie) vs. Sw (ratio), and (5) Rt/Rw vs. Rxo/Rmf (dew plot).

A crossplot of core-derived porosity vs. permeability was used to establish a 15% porosity cutoff for a permeability of 1.0 md. The high (15%) porosity cutoff is the result of the fine grain size and the authigenic clays. Core-derived cementation exponents (m) averaged 1.85. This value was used to calculate Archie water saturations for the net pay determinations.

Using net pay cutoffs of Vcl < 15% (dispersed clay), effective porosity (fe) > 15% (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-feet thickness of 5.1 ft, which calculates into 1.6 million bbl in place assuming 40-ac drainage.

AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.