Aspects of time-lapse electrical resistivity monitoring in geotechnical and reservoir problems

Abstract

Internal erosion can be present in almost any environment in which fluid flows through a rock matrix. In almost all cases this phenomenon is a problem to be avoided. Internal erosion weakens the rock structure, which can cause collapse of the surrounding matrix. In the geotechnical field, this is most common with earthen dams and levees. The consequence of internal erosion in an oil and gas reservoir setting is to create a high-permeability link between injection and production wells, by-passing resource containing volumes of the reservoir. In this thesis, I present feasibility studies to examine the effectiveness of electrical resistivity tomography (ERT) for monitoring both fluid flow and the resultant internal erosion. This is conducted in both the laboratory and reservoir scales. Because the success of ERT is highly dependent on the configuration of electrodes, significant time is spent on developing configurations that image internal erosion while also limiting the number of data required. This work gives evidence that ERT can have beneficial use in the geotechnical monitoring scenario. The feasibility study for the small-scale geotechnical experiment on internal erosion shows that a 10 cm diameter sample can be imaged effectively when the electrode configuration is properly designed. This feasibility study is further confirmed through a data set collected in the laboratory. This experiment produced sufficient results in terms of the model recovered through inversion. The feasibility study evaluating ERT in a reservoir setting shows that the monitoring target is the total 410 m long swept zone, rather than the small fractures, due to low signal strength from the fractures. The capability of ERT in the reservoir scenario depends on the degree of internal erosion and the electrode configuration used to take measurements. If data can be collected in boreholes in close proximity to the swept zone, then ERT has a potential beneficial application in monitoring fluid flow and associated fractures.