Speaker: Nikita Seleznev, Schlumberger-Doll Research (SDR) center
Date: Thursday, Feb 22nd, 2018
Time: 11:30 am -1:00 pm
Location: Weatherford Lab
Parking: One story building with surface parking. Visitors are requested to reverse park, note their license plate number and sign in at the main reception.
RSVP by noon, Monday before meeting Time: Lunch 11:30, Presentation at 12:00
Cost: $15-industry professionals/$10-students
Electromagnetic formation evaluation currently relies on low-frequency resistivity and high-frequency dielectric measurements that are typically not interpreted jointly. In consideration that formation electromagnetic responses in different frequency ranges are controlled by different physical phenomena, analysis of a wideband electromagnetic response can provide new and complementary sensitivities to formation petrophysical parameters.
Frequency-dependent complex conductivity of ion-conductive sediments in the range from millihertz to kilohertz exhibits the spectral induced polarization (SIP) effect, in which the impedance phase has a near-resonance peak at characteristic frequency due to strong polarization response. SIP spectra were measured on a collection of quarried clean sandstones saturated with brines. The influence of other factors on the SIP effect, such as the presence of clays, was minimized by carefully selecting samples. Dielectric dispersion was measured to characterize a subset of twin samples in the megahertz to gigahertz range. The combination of these methods provided core electromagnetic responses over 12 decades of frequency.
We established a wideband rock model based on a differential effective medium approach that accounts for both the Maxwell-Wagner interfacial polarization related to the rock texture and the electrochemical polarization due to the presence of charged grains. The model is based on first principles and uses a minimal number of parameters to describe the essential electromagnetic properties of sandstones in the millihertz to gigahertz range.
We investigated the relationship between the SIP effect and the dominant grain size of our sandstone collection. Dominant grain size was determined using digital image analysis of scanning electron microscope (SEM) images obtained on thin sections. SIP spectra were inverted with the rock model to obtain the dominant grain size. The model was shown to be capable of reproducing well the experimental SIP spectra, with the inverted dominant grain size comparing favorably with values determined from image analysis.
We analyzed the wideband electromagnetic measurements by applying the rock model in the full frequency range. Wideband data inversion enabled the estimation of five formation parameters: water-filled porosity, water salinity, cation exchange capacity, dominant grain size, and cementation exponent. Our analysis also demonstrated that the use of only low- or only high-frequency data subsets is not sufficient to reliably invert the full set of formation parameters.
The ability to invert for a broad set of formation parameters provides comprehensive characterization that is unattainable with currently practiced methods. Besides providing grain size as a new petrophysical parameter from electromagnetic formation evaluation, the methodology eliminates interpretation uncertainties associated with current approaches in which some parameters are independently provided as input.
Nikita Seleznev is a Principal Scientist and Petrophysics Program Manager at Schlumberger-Doll Research (SDR) center in Cambridge, MA. He joined Schlumberger in 1998 as a Wireline field engineer. Since 2000 he has been conducting research at SDR in dielectric and resistivity logging tools and techniques as well as various other aspects of Petrophysics of conventional and unconventional reservoirs. His current interests include formation evaluation with wideband electromagnetic methods and petrophysical applications of the dielectric dispersion logging for unconventional reservoirs. Nikita obtained PhD in Petrophysics from the Delft University of Technology, The Netherlands. Nikita is a member of the SPWLA Technical Committee.