This paper is a pan of an on-going research project at The Pennsylvania State University, aimed at correlating rock/fluid properties to oil recovery from various types of hydrocarbon bearing porous media. This report deals with an experimental and theoretical studies to investigate certain rock/pore properties of limestone rocks that previously have not been fully investigated and correlated to waterflood oil recovery at breakthrough and ultimate oil recovery. Apart from porosity and permeability, the other rock/pore properties investigated are tortuosity, formation relativity factor, wettability index, pore intrusion volume, pore, surface area, pore-throat diameter, pore skeletal density and recovery efficiency.
To accomplish the above stated objective, waterflood experiments were conducted on 16 limestone linear-cores ranging in length from 40.0 cm to 45.7 cm in length and diameter from 3.76 to 3.89 cm. The cores were flooded at different rates depending on their scaling coefficient (product of core length in cm, water velocity in cm/min and water viscosity in cp), which was kept at an approximately constant value of 5.0. The limestone rocks investigated were mainly from the Indiana limestone units which were formed in shallow inland sea during Mississippian time.
Thirty-two core plugs were extracted from each of the waterflooded cores from positions perpendicular to the flood plane (for a total of 512 core plugs) and further analyzed by conducting the wettability and mercury porosimetry experiments. The cores investigated were all water-wet and the results of the mercury porosimetry experiments suggested that bimodal pore-size distributions are characteristic of the limestone core samples.
The results of these tests are presented and incorporated into empirical models for the prediction of oil recovery at breakthrough and at floodout, from waterflooding for limestone reservoirs. The models indicated that waterflood limestone oil recovery is strongly correlated to porosity, formation resistivity factor, wettability index, irreducible water saturation, residual oil saturation, pore intrusion volume, pore surface area, pore specific surface area and mercury recovery efficiency.
One of the requirements for understanding waterflood performance is a good knowledge of the basic properties of the reservoir rocks. This study is aimed at investigating the characteristics of fluid flow mechanism in water-wet limestones exhibiting bimodal pore-size distribution. These characteristics are then incorporated into empirical models for predicting warerflood oil recovery at both breakthrough and floodout. For that reason, this report deals with the analyses and interpretation of experimental data collected from core floods and correlated against measurements of porosity, tortuosity, formation resistivity factor, wettability index, irreducible water saturation, residual oil saturation and mercury porosimetry properties.
The most important component of reservoir characterization is the description of the pore systems, which is one of the factors that control the production potential of the reservoir. Pore systems are studied by a family of methods called perrophysical analysis; one of these methods is mercury porosimetry. In this method, mercury is injected into the pore system of a sample under controlled conditions, to produce capillary pressure curves.
