TABLE OF CONTENTS Porosity is defined as the interstitial void space in a rock. Permeability is a property of rock (usually sedimentary rock) that characterizes the ease with which fluid can flow through it in response to an applied pressure gradient. Both of these properties control the ability of a rock to store (via porosity) and transmit (via permeability) reservoir and nonreservoir (injected) fluids. Capillarity is defined as "the attraction of the surface of a liquid to the surface of the solid with which it is in contact. Capillarity affects the recovery of oil from a reservoir as it hinders the oil from flowing through the pores of the rock" (Hyne, 1991).
This chapter emphasizes the important geologic factors that control reservoir quality (porosity and permeability) in oil and gas reservoirs. These factors include primary depositional texture (grain size and grain sorting) and postdepositional processes (physical-chemical) of burial diagenesis. Diagenesis controls the final geometry of the pore structure, grain orientation and packing, and the degree of cementation and clay filling of pore spaces.
Pore spaces can be examined directly in sedimentary rocks, either in a hand sample or by cutting a "thin section" (0.030 mm thick) of the rock. To prepare a thin section, a small slab of rock is cut from the larger sample and is placed in a chamber containing colored epoxy (normally, either blue or red). Then, either pressure or a vacuum is applied to the sealed...
