Date of Award
Master of Science (MS)
Murdoch, Lawrence C
Falta , Ronald W
Moysey , Stephen
Fractures are ubiquitous in the shallow crust and they commonly control the flow and storage of fluids in rock. Estimating transmission and storage properties resulting from fractures is commonly accomplished by interpreting the pressure signals caused by stressing an aquifer during a pumping or slug test. Fractures deform in response to pressure changes during well tests, and measuring and interpreting the deformation along with the pressure change is a way to potentially increase the information about storage and transmission properties. Tests where the pressure and deformation are coupled are called hydromechanical well tests. Previous investigations have focused on the effects of hydromechanical slug tests that use a single well. The single well slug test approach has the advantage of simplicity because it only requires one well, but it is limited in resolution compared to tests using multiple wells. The objective of this research is to improve understanding of fractured rock aquifers by including responses in monitoring wells and by integrating other data, such as borehole camera surveys, into well tests. The approach is to first characterize the response of a slug test using one source and one monitoring well by conducting theoretical analyses and field tests. The investigation shows that when the pressure is increased in the source well, the pressure change commonly drops in a monitoring well before it increases to give the expected signal. This reverse-water-level change in the monitoring well differs fundamentally from a similar response (the Noordbergum and Rhade effects) observed during pumping tests in confined aquifers because it occurs in the same fracture stressed by the well, whereas those other classical effects occur in confining units overlying aquifers.
The investigation is expanded by conducting multiple tests using different combinations of wells to determine permeable paths formed by fractures. A simple search algorithm is used to first locate connections between long permeable intervals in boreholes, and then the lengths of the intervals are progressively reduced to refine the resolution. Straddle packers are used to isolate individual fractures identified using camera surveys in order to refine the resolution even further. The result is the 3-D permeable network created by the fractures in the vicinity of the wells.
Slack, Trever, "Hydromechanical Interference Slug Tests in a Fractured Biotite Gneiss" (2010). All Theses. 934.