Seismoelectric response of heavy oil reservoirs: theory and numerical modelling

Abstract

International audienceWe consider a linear poroelastic material filled with a linear viscoelastic solvent like wet heavy oils (oil as opposed to water or brines is wetting the surfaces of the pores). We extend the electrokinetic theory in the frequency domain accounting for the relaxation effects associated with resonance of the viscoelastic fluid. The fluid is described by a generalized Maxwell rheology with a distribution of relaxation times given by a Cole–Cole distribution. We use the assumption that the charges of the diffuse layer are uniformly distributed in the pore space (Donnan model). The macroscopic constitutive equations of transport for the seepage velocity and the current density have the form of coupled Darcy and Ohm equations with frequency-dependent material properties. These equations are combined with an extended Frenkel–Biot model describing the deformation of the poroelastic material filled with the viscoelastic fluid. In the mechanical constitutive equations, the effective shear modulus is frequency dependent. An amplification of the seismoelectric conversion is expected in the frequency band where resonance of the generalized Maxwell fluid occurs. The seismic and seismoelectric equations are modelled using a finite element code with PML boundary conditions. We found that the DC-value of the streaming potential coupling coefficient is also very high. These results have applications regarding the development of new non-intrusive methods to characterize shallow heavy oil reservoirs in tar sands and DNAPL contaminant plumes in shallow aquifers

Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing

“…Moreover, seismograms and electrograms at the observation site correlated well with each other [10,[15][16][17]. Theoretical and observational studies indicated that there were linear relations between the electric field and seismic velocity [10] or acceleration [17], with the coefficient (transfer function) depending on the kinetic property on the site.…”

“…from the ordinary coseismic variation moving with the seismic wave as recorded and studied so far [9,10,12,[14][15][16][17][18][19][20][21][22][23]. This is the first report of the detection of this kind of electric variation, that is, correlation with the seismic wave starting from the beginning of fault rupture, in our long history of electric field measurement by using a borehole antenna.…”

“…At the first stage of the analysis of the phenomenon, the B anomalies (Figure 2(a)) at Hasaki were thought to be well-known coseismic electric variations observed and reported in numerous papers [9,10,12,[14][15][16][17][18][19][20][21][22][23]. They correlated in general with the ground surface fluctuation Figure 1).…”

“…Recent application of seismoelectronics to exploration surveying has resulted in finding and confirming the coseismic electromagnetic field [14][15][16][17]. However, we need more data to understand the phenomenon to build a consistent generation model and to develop application technology based on this phenomenon.…”

“…The seismic wave speed is about 6 km/s for the primary (P) wave and 3.5 km/s for the secondary wave [1,2] in the upper crust. There have been many reports on the electromagnetic phenomena of earthquakes and volcanic eruptions (e.g., [3][4][5][6][7]), but only a few papers have dealt with the field observation of electromagnetic variation that started just after the rupture of the fault [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Belov et al [8] detected associated electromagnetic fields about 10 seconds before the seismic wave arrival and 4 seconds after the origin time.…”