Application of Land-Based Controlled Source EM Method to Hydraulic Fracture Monitoring

Abstract

Hydraulic fracturing allows improved hydrocarbon production in low permeability formations. Imaging the distribution of fluid used to create a hydraulic fracture can aid in the characterization of fracture properties such as extent of fluid penetration as well as fracture azimuth and symmetry. This could contribute to improving the efficiency of an operation, for example, in helping to determine ideal well spacing or the need to refracture a zone. A ground-based controlled-source electromagnetics (CSEM) technique shows promise for imaging the fluid due to the change in field caused by the difference in the conductive properties of the fluid when compared to the background. With sufficient advances in high signal to noise recording equipment, coupled with a high-power, broadband transmitter one could potentially detect hydraulic fracture extent and azimuth with minimal processing. In this study, a 3D finite element code is used to model the complete well casing along with the layered subsurface. The forward modeling is used to optimize survey designs and identify the band of frequencies that best capture the desired subsurface response. In the field, the results of the modeling are also used to create a custom pseudorandom numeric (PRN) code to control the frequency content of transmission through a grounded dipole source. Receivers record the surface voltage across two grounded dipoles, one parallel and one perpendicular to the transmitter. The data are presented as the displays of amplitude ratios across several frequencies at the various receiver locations. I show field results in multiple basins in the United States along with the CSEM theory used to create the survey designs. Interpretations of CSEM responses in terms of subsurface changes in electrical conductivity presented in this dissertation are regarded as tentative awaiting further tests from detailed numerical simulations and a better understanding of noise. Oilfield operations are exceedingly complex systems and the CSEM technology for hydraulic fracture monitoring, while showing promise, is still under development.