Feedsee Energy : Oil Sands : Analyzing porosity, permeability, fluid content, geological age, and probable productivity
In 2007, the first Lexcore Services rigs moved from the Fort McMurray area to the Peace River area to begin the second phase of Laricinia Energy's oil sands exploration project. "This next area of drilling near Wabasca is going to give our rigs the opportunity to demonstrate their full potential," said Dan Nanninga of Lexcore. Oil sands companies evaluate oil sands by drilling evaluation holes and removing core samples, necessary in Alberta's expanding oil sands where traditional seismic exploration is not nearly as effective. Coring involves cutting a cylindrical sample out of the earth during drilling to allow geological analysis of what lies below. The geological analysis determines the location's physical characteristics such as porosity, permeability, fluid content, geological age, and probable productivity.
How Oil Sands are Evaluated
Evaluating oil sands for their commercial potential is a complex process that requires a wide array of geological, petrophysical, and engineering techniques. Here's a general outline of how these various factors might be evaluated:
- Porosity: Porosity refers to the proportion of void space in the rock where oil can reside. It can be measured by examining rock samples under a microscope or by using well logging tools that measure properties such as density or neutron response. Core samples taken during exploratory drilling can be particularly useful for this. These samples are analyzed in laboratories to measure their porosity directly.
- Permeability: This is a measure of how easily fluids can flow through the rock. It can be directly measured on core samples in the lab, or inferred from well log responses. Sometimes, it's also measured by conducting well tests, where fluid is pumped into or out of the well and the pressure response is observed.
- Fluid Content: Fluid content refers to the type and amount of hydrocarbons present in the rock. Samples of the rock (cores) and of the fluids (usually obtained during well testing) are taken and analyzed in the lab to determine the types and quantities of hydrocarbons they contain. Logging tools can also provide information about fluid content. For instance, resistivity logs can give indications about the presence of hydrocarbons (which are resistive) versus water (which is conductive).
- Geological Age and Stratigraphy: The age and stratigraphic position of the rocks can be determined using a variety of techniques, including the study of fossils (paleontology), the magnetic properties of the rocks (paleomagnetism), and correlations with other well data. Understanding the geological history of the area can also help in predicting where the best reservoir rocks might be found.
- Probable Productivity: This can be a complex calculation that involves all the other factors, plus the pressure and temperature of the reservoir, the thickness of the oil-bearing rocks, and the likely decline rate of the well over time. Productivity can also be influenced by the viscosity of the oil, which in oil sands can be very high. This can necessitate the use of techniques such as steam injection to enable the oil to flow.
This evaluation process requires a multidisciplinary team, including geologists, petrophysicists, reservoir engineers, and others. The process can take considerable time and resources, and involves a degree of uncertainty. But the potential rewards of finding a commercially viable oil sands deposit can be substantial.