T52 Geological and Hydrogeological Characterization Studies at CO2 Sequestration Sites

Sunday, 4 November 2012
1:30 PM - 5:30 PM
213A

WELLBORE DEFORMATION AS A MONITORING AND ASSESSMENT TOOL DURING CO2 SEQUESTRATION

Paper number: T52-15
Program: Technical Sessions
Time: 4:50 PM – 5:05 PM

Authors

Abstract

Well bores deform in response to injection or recovery of fluid, and this signal may be used to reduce risks during CO2 sequestration. The feasibility of using wellbore deformation as a diagnostic tool is being evaluated by addressing three primary questions: What is the magnitude and pattern of expected deformation? Can this signal be measured? Can these measurements be interpreted? The first question is being evaluated by developing a series of theoretical analyses that represent wells in various scenarios typical of CO2 sequestration. The conceptual model that emerges is that well casing is an elastic tube that is loaded during the well completion process. This external load compresses the casing, and during injection the casing moves both radially and axially. Internal fluid pressure causes the casing to bulge outward, and poroelastic effects in the injection formation unload the casing and cause it to deform. Pressure on adjacent confining units, and interaction with the ground surface cause the casing to stretch longitudinally where it contacts the injection interval, and it can be compressed in the overlying confining units. Typical radial displacements are on the order of tenths of microns to several microns, and axial strains up to 10 microstrain seem feasible, according to simulation using poroelastic codes.

Measuring small deformations in deep wells will be required for this technique to be viable. We have evaluated the feasibility of using high resolution electromagnetic sensors, fiber optic strain gauges, as well as electrolytic tiltmeters for this application. The evaluation process has included the development and evaluation of prototype downhole tools designed to measure radial, axial and 3D deformations. Field testing of these tools demonstrate that it is possible to measure displacements less than 0.1 micron, and strains of less than 0.1 microstrain at depths of several 10s of meters. These results are encouraging because they suggest that it could be feasible to measure deformations indicated from the theoretical analyses. We are also developing inversion methods using Markov Chain-Monte Carlo techniques for quantitative parameter estimation and uncertainty evaluation.