Spectral Induced Polarization for petrophysical estimation of complex reservoir

INTRODUCTION

  • Spectral Induced Polarization is a non-intrusive approach, sensitive to the surface conductance of the mineral grains, the frequency dependent polarization of the electric double layer and the bulk conductance of the pore water.

METHODOLOGY

Step 1: Dry the samples in oven at 60 ℃ for 2 days.

Step 2: Put the samples in saturation with tap water under vacuum as shown in Fig 2..

Step 3: Wait for atleast one month to fully saturate the samples. To check the saturation, I measured the weight of the samples after every 2-3 days.

Step 4: When the weight is stable, prepare the sample for complex conductivity measurements.

Step 5: Prepare the known brine solution of different conductivities and measure the complex conductivity measurements.

Figure 2

MEASUREMENTS :

  • To measure the spectral induced polarization or also known as complex conductivity, we need an impedance meter of frequency range between 0.1 mHz-45 kHz.
  • Non-polarizable electrodes are needed.
  • The core sample is connected to the impedance meter using the current and potential electrodes.

Fig 3: Complete setup of complex conductivity measurements

RESULTS :

The real and imaginary part of the impedance along with the phase is measured using the impedance meter. The real part and imaginary part of the conductivity is measured as:

σ^′=K∗Real(R)/(Abs(R))^2

σ^”=-K∗Imag(R)/(Abs(R))^2

Where, K is the geometric factor

K=(πr^2)/(Length of sample)

Fig 6: In-phase conductivity (real part) and quadrature conductivity (imaginary part) obtained from complex conductivity measurements at four different salinities.

Fig 7: Impact of clay content (cation exchange capacity) on quadrature conductivity.