Induced polarization effect in land and marine CSEM data: applications for hydrocarbon exploration
Creators: name: Buist, Samuel I
Publisher: name: University of Utah
Year: 2012
Subjects: Petroleum prospecting
Electric prospecting

description: The recent improvements in data acquisition and data interpretation techniques,  and the encouraging results obtained by Russian and Chinese geophysicists using  the induced polarization (IP) method have stimulated a renewed interest in its  use in hydrocarbon (HC) exploration. In this thesis we show the results of IP  measurements conducted on shale HC source rocks samples, and apply the information  gained to model typical geoelectrical formations of onshore and offshore  HC deposits. With these results we can consider the feasibility of detecting a  measurable IP response associated with the deposit. We also develop and test an  inversion technique for quantitative interpretation of the IP data.  Over recent years a large amount of effort has been applied to understanding  and improving the inversion theory for recovering a true model in a controlled  source electromagnetic (CSEM) setting. Most recent 3D inversion schemes are  inverted strictly for real resistivity values even though there is sufficient evidence  that the resistivity of rocks is described by a complex function. This property  of rocks is manifested by the IP phenomenon and its principles have been used  extensively in the search for mineral deposits for many years. Historically, this  method of investigating the complex resistivity has been restricted to land based  IP surveys. In this thesis we show that a similar technique can be used for offshore  HC exploration.  The Cole-Cole conductivity model is tested with complex resistivity data and  detailed mineralogy of hydrocarbon bearing shale rock samples. Inversion routines  are developed and tested using synthetic data to recover the three empirical variables  from recorded complex resistivity data. These empirical variables are the  decay coefficient (C), chargeability (m), and the time constant (T). For three shale samples, detailed geologic analysis using QEMSCAN was conducted to help better  understand the inversion results.  Complex resistivity values are calculated from recorded EM data from 0.0156 Hz  to 9216 Hz. Using the observed mineralogical data we were able to fit the recorded  complex resistivity data using the Cole-Cole model for two of the three samples  and a spherical inclusion, three-phase Generalized Effective Medium Theory of IP  (GEMTIP) model for the last sample. The results showed both the effects of electrode  and membrane polarization at different frequencies. The gained knowledge  from the QEMSCAN results helped in understand how varying grain size and pyrite  concentration controls the IP effect.  Forward geophysical modeling of hydrocarbon systems is accomplished using  geologic inputs from the shale sample analysis to deposit-scale HC models. The  IBCEM3DIP code which is based on the Integral equation method, developed by  the Consortium for Electromagnetic Modeling and Inversion (CEMI), is used for  forward modeling.  Using the developed HC models, the effect of deposit-scale changes in Cole-Cole  parameters is tested on synthetic IP data. The results clearly show that while the  membrane polarization is at the lower end of IP detectability, the electrode polarization  (from pyrite) is at the very high end. Thus it should be easily detectable,  even in an environment with a higher level of noise. We have also proved that  one can invert for both the real and imaginary parts of the EM signal in a marine  setting with sufficient accuracy to delineate between the two bodies.  With advances in the understanding of the IP effect through IP modeling,  forward modeling and inversion, detection and discrimination capability will be  improved for hydrocarbon source and possible reservoir targets, leading to a greater  efficiency in petroleum exploration.