Adams, Aaron J.¹, Wayne M. Ahr¹
(1) Texas A&M University, College Station, TX

ABSTRACT: Connectivity in Carbonate Reservoirs: Solving Tough Plumbing Problems

Identifying and mapping connected pore systems in carbonate reservoirs is difficult. Pore characteristics in Jurassic Smackover reservoirs at Vocation-Appleton & Womack fields, Alabama, were examined with petrographic image analysis (PIA) in combination with NMR and MICP measurements on the same samples. PIA provides porosity values, pore sizes, and pore roundness. T2 relaxation times from NMR runs discriminate between “large” and “small” pores. MICP measures median throat diameters. Neither NMR nor MICP provide information about pore origin. We identified and evaluated 3 pore “facies.” Type 1 includes depositional (grain-supported) pores. Porosity from core analysis correlates moderately (R2=.74-.85) with PIA measurements, which show that 60-80% of these pores are 100-1000µm2 in size, most T2 relaxation times are 100-1000ms, and have median throat diameters of 1.3-3.3µm. Type 2 includes diagenetic (intercrystalline/moldic) pores with moderate (R2=.68) correspondence between core analysis and PIA values. 70-90% of these pores measure 100-1000µm2 in size and NMR T2 relaxation occurs in both bi and trimodal forms. Type 3 pores are of diagenetic origin (intercrystalline/vuggy), they exhibit moderate (R2=.80) correlation between core analysis and PIA values, 40-70% of the pores range from 100-1000µm2 in size, and 25-45% of pores measure >1000µm2. T2 relaxation times vary as a function of vug size, i.e., T2 times on large vugs occur at ~400ms. MTD likewise varies from 1.2-26.1µm depending on pore type and geometry. We are now developing a ranking scheme to assign relative reservoir quality to each pore facies.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.