Wayne M. Ahr1
(1) Texas A and M University, College station, TX
Abstract: Carbonate pore properties as indices of reservoir quality
Optimum combinations of porosity and permeability sometimes indicate high connectivity and low resistance to fluid transmissivity in carbonate reservoirs. These zones, or "flow units", may have pore systems that include any combination of 3 genetic pore classes; therefore, flow units may reflect structural, depositional diagenetic, or hybrid genetic characteristics. Pore classes within flow units can be "ranked" for high intermediate, and low recovery efficiency. The latter based on mercury withdrawal efficiency in capillary pressure runs. Carbonates at Happy Spraberry field Garza County, TX, consist of about 100 feet of oolitic-peloidal grainstones, oolitic-peloidal packstones, and skeletal rudstones, bindstones, and floatstones. Major rock types have distinctive pore properties that reflect their geological history: e.g., leached depositional porosity on paleo-highs where probable unconformity-related dissolution was effective. Principal pore types in this field are grain-molds, vugs, solution-enlarged intergranular pores, and cement-reduced pores. Flow unit boundaries are loosely facies-selective and were defined by comparing poroperm values from core analyses with pore properties from thin section petrography. The results defined links between genetic pore classes and poroperm values ("pore facies"). Pore facies were ranked as best, intermediate, and poor quality on their capillary pressure character, median pore throat size, and mercury withdrawal efficiency. Pore facies map overlays on facies maps identified spatial distribution of quality ranked pore facies within flow units.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana