Environmental and Reservoir Geophysics

Objectives: The course aims to show how geophysical data can be used to reveal fluid composition and other reservoir properties of both near-surface sediments and subsurface reservoirs. This is important for monitoring effects of long-term increase in surface temperatures related to thawing of the Arctic sedimentary landscape and the following environmental impacts. This is also important for understanding time lapse geophysical effects of subsurface reservoirs subjected to injection of carbon dioxide or production of hydrocarbons. 

The course explains the physical principles and models needed to extract the relevant information of near-surface sediments from seismic surface waves, and subsurface reservoirs from seismic reflection data. The course moreover introduces other geophysical methods based on electromagnetic and radar surveying together with information from well data (density, acoustic and resistivity logging) which can further improve reservoir delineation from seismic data.

At the end of the course, the student shall know the basic principles behind the methods and be able to diagnose and solve basic problems related to reservoir characterization and monitoring, and, furthermore, be able to discuss possible sources of error attached to the results.

Content: The course has a thematic structure, starting with an introduction of the fundamentals of sedimentary rocks which influence their reservoir properties. The following module introduces the physical principles behind deriving various geophysical properties of rocks, like seismic, electromagnetic, and geothermal properties. The next module discusses various rock physics theories and methods used to link reservoir properties to the various geophysical properties cited above. The next module presents the basics of 1) near-surface geophysical surveying with particular emphasis on use of seismic surface waves, and 2) reflection seismic surveying with particular emphasis on use of seismic attributes obtained from the variation of seismic reflection amplitudes with offset (amplitude versus offset). Finally, rock physics and geophysical data are combined to delineate reservoir conditions, and, furthermore, by using time lapse geophysical data to monitor altered reservoir conditions with time.

On completion of the course the student should have the following learning outcomes defined in terms of knowledge, skills and general competence:

Knowledge: 

The student should be able to:

• define the various geophysical properties of rocks.
• discuss various reservoir properties of near-surface sediments and subsurface rocks.
• review the most important principles and models for calculating geophysical properties of unconsolidated and consolidated sediments.
• discuss geophysical effects of freezing and thawing of near-surface sediments due to altered water-to-ice ratio.
• review principles for acquisition and utilization of near-surface geophysical data.
• discuss geophysical effects of subsurface reservoirs due to altered reservoir fluid composition, porosity, and pressure.
• review various seismic attributes related to reflection amplitude variation with offset.
• discuss methods enabling direct reservoir delineation from geophysical data.

Skills: 

The student can:

• from sediment composition data calculate thermal, seismic, and electromagnetic properties.
• calculate seismic effects caused by thawing/freezing processes of near-surface sediments.
• perform seismic modelling of near-surface data and characterize various surface wave signatures.
• calculate how increased burial depth and temperature alter reservoir properties and geophysical properties.
• compute effects of altered reservoir conditions on geophysical properties.
• perform simple amplitude versus offset analysis and apply this in reservoir analysis.
• construct so-called rock physics templates for use in quantitative seismic interpretation.

General competence: 

The student can:

• use precise terminology to discuss various types of geophysical data and how they can be measured.
• review and discuss strategies for geophysical monitoring of increased heat-flux into arctic near-surface terrestrial sediments and the following impacts on environmental conditions.
• review and discuss strategies for enhanced geophysical reservoir characterization and quantitative seismic interpretation of subsurface reservoirs.
• review and discuss strategies for geophysical monitoring of subsurface reservoirs caused by injection of carbon dioxide and possible leakage.