Rocks, Holes and the Fire Brigade: Understanding the Pore Geometry of Reservoir Rocks

By

John G. Kaldi

National Centre for Petroleum Geology and Geophysics, University of Adelaide, South Australia, and C. VAVRA, North Star Geological, TX

There is a marked similarity between the role of fire brigades the world over and geologists and engineers working on detailed pore-level reservoir characterization. Fire fighters deal with "recovering" people from burning buildings. Part of their success or failure (the "recovery efficiency") is controlled by the internal architecture of the buildings (i.e., the configuration of rooms and doors and corridors of various shapes and sizes). Pore geometry exerts a direct control on the amounts, types, and rates of fluids produced from the reservoir. Pore geometry refers to the size, shape, and distribution of pores and pore throats in a reservoir rock. Pore geometry is reflected in capillarity and relative permeability and thus influences both saturation vs. height properties and the relative quantities of fluids produced. It is possible to relate pore geometry to capillary pressure data (both drainage and imbibition curves) to evaluate recovery efficiency of reservoirs on primary depletion as well as to judge the distribution of remaining fluids prior to secondary production. In addition, potential formation damage-prone intervals can be identified from the understanding of pore geometry in conjunction with detailed rock properties such as mineralogy and clay morphology. Pore geometry is evaluated using fairly routine analytical techniques such as petrography, pore casts, mercury injection capillary pressure, and relative permeability curves. An understanding of the pore geometry of reservoir rocks early in production is desirable in order to predict reservoir behavior during field life.

AAPG Search and Discovery Article #90015©2002-2003 AAPG Distinguished Lectures