Petrophysics MSc Course Notes by Dr. Paul W.J. Glover

The initial step in the search for oil and gas deposits involves identifying areas with favorable geological conditions. These areas, called geological provinces, are characterized by specific rock formations, structures, and depositional environments that are conducive to oil and gas accumulation.

Caliper logging is a wireline logging method used to measure the diameter of a borehole. This data provides information about the borehole's shape, size, and any irregularities. The information gathered from caliper logging is crucial for evaluating the borehole environment before and during oil and gas production.

Neutron logging is a method used to measure the hydrogen content of a formation. By measuring the hydrogen content, petrophysicists can determine the porosity of the formation efficiently. The neutron log plays a crucial role in evaluating the reservoir's storage capacity.

The formation density log is a wireline logging method used to measure the bulk density of a formation. This information helps determine the total density of the rock, including the minerals and fluids present. The formation density log is crucial in calculating the volume of fluids contained in the reservoir.

Resistivity theory in petrophysics is the study of how electrical currents flow through rocks. By understanding the electrical properties of rocks, petrophysicists can identify and differentiate between fluid types (oil, gas, water) and estimate the amount of hydrocarbons present in a reservoir. This knowledge helps in optimizing the production of oil and gas.

The exploration geologist plays a vital role in analyzing sub-surface formations by correlating wireline responses. This means identifying patterns and similarities in the log data from different wells to create a large-scale image of the geological formations present. This image provides essential context for understanding the reservoir's structure and potential fluid distribution.

The initial aim of a petrophysicist when analyzing sub-surface formations is to differentiate between oil, gas, and water-bearing zones. This identification is essential for determining the economic potential of a reservoir. By understanding the fluid types present, petrophysicists can predict the reservoir's behavior and optimal recovery strategies.

Petrophysicists play a key role in carrying out initial reservoir modeling. This involves using wireline log data and other information to create a digital representation of the reservoir. This model helps predict the reservoir's behavior, estimate resource potential, and guide future development decisions.

Geologists contribute to evaluating sub-surface formations by focusing on understanding the lithology, stratigraphy, and depositional environment. They identify the types of rocks present, their arrangement, and how they were originally deposited. This geological information helps petrophysicists interpret wireline log data accurately and understand the reservoir's history.

Wireline log data is a primary database that provides crucial information for both geologists and petrophysicists. This data is collected from various logging tools run down a wellbore. The information from wireline logs helps identify rock types, fluid types, and reservoir characteristics, forming a foundation for understanding the subsurface formations.

Capillary pressure is a key concept in petrophysics that helps determine the size and distribution of pores within a rock. It's the pressure difference between the fluids in the pores and the surrounding rock. By analyzing capillary pressure data, petrophysicists can understand how fluids are held in the rock and how much fluid can be produced from the reservoir.

The total gamma ray log is used to measure the natural radioactivity of the formation. This measurement is helpful in identifying different rock types based on their radioactive content. The gamma ray log is a crucial tool in stratigraphic correlation and identifying potential hydrocarbon-bearing zones.

Clay, while not a primary reservoir rock, influences the reservoir's properties. It increases the rock's resistivity because clays are non-conductive. However, clays reduce porosity because they can fill up pore space, making it difficult for fluids to flow. This is crucial for petrophysicists to account for when evaluating reservoir quality.

The sonic log primarily measures the acoustic velocity of sound waves traveling through the formation. This information provides insights into the rock's physical properties, including its hardness and the amount of fluids present. The sonic log is crucial in calculating the compressibility of the rock, which is important for reservoir management and production planning.

Fluid testing and pressure logs are used to evaluate the composition and behavior of fluids in the reservoir. This information is critical for determining the type of fluids present (oil, gas, water), their pressure, and how they behave at different depths. Fluid testing and pressure logs help optimize production strategies and minimize risks associated with reservoir management.

Petrophysicists are responsible for designing reservoir management strategies based on the analysis of sub-surface formations. They use wireline log data, core data, and other information to optimize production, minimize risks, and maximize recovery of hydrocarbons. Their expertise ensures that the reservoir is managed efficiently and sustainably.

The exploration geologist plays a crucial role in evaluating sub-surface formations by creating a large-scale image of the subsurface geology. They use wireline log data and other information to map out the distribution of rock formations, structures, and potential hydrocarbon-bearing zones. This information guides drilling decisions and helps understand the overall context of the reservoir.

Resistivity theory in petrophysics is used to estimate the porosity of formations. By measuring how easily electrical currents flow through rocks, petrophysicists can estimate the amount of space filled with fluids. This estimation helps determine the reservoir's storage capacity and its potential for producing hydrocarbons.

The exploration geologist plays a crucial role in correlating wireline responses characteristic of a given formation. This involves identifying patterns and similarities in the log data from different wells to understand how a specific formation changes over time and space. This information helps in mapping the formation's extent and identifying potential hydrocarbon traps.

Wireline log data and data from experiments on extracted cores are key databases for both geologists and petrophysicists. This data provides information about the rock properties, fluid types, and reservoir characteristics. By combining these information sources, they can create a comprehensive understanding of the subsurface formations and guide future exploration and production decisions.