Integration of multiple electromagnetic imaging and inversion techniques for prospect evaluation

Abstract

The use of controlled source electromagnetics (CSEM) in the marine environment has grown rapidly in the past few years from a simple anomaly fluid-hunting technique used in geologically simple environments to a modeling and inversion based technique applied in structurally and lithologically complex environments . The tool set most commonly available to interpreters includes one-, two-and three-dimensional forward and inverse modeling codes. All previous examples, reported in the literature, of inversion codes applied to marine CSEM data have been cell-based regularized techniques designed to produce the smoothest possible isotropic conductivity model (in two-or three-dimensions) which fits the observed data. We report on the development of a new technique, anisotropic sharp-boundary inversion in which the model is parameterized by two-dimensional interfaces. In this approach anisotropic conductivity can have sharp contrasts across interfaces. Regularization is applied to the smoothness of the interface and the lateral variations of conductivity between interfaces. We demonstrate a work flow that progresses from forward modeling through fast depth migration to smooth cell based inversion, concluding with sharp boundary inversion for the final interpreted conductivity image.

Resolution of reservoir scale electrical anisotropy from marine CSEM data

“…This leads to the intriguing possibility of making permeability estimates in hydrocarbon filled sands from inferred electrical anisotropy if such an inference were possible. This also means that the transition from regions of isotropic resistivity to regions of anisotropic resistivity would mark the transition from water to oil within reservoir sands, as demonstrated by Klein et al (1997). A third related application is the use of the horizontal and vertical resistivity as independent data in stochastic rock physics simulations of fluid type, where the ability to accurately determine horizontal resistivity is essential.…”

“…The effect of this macro-scale electrical anisotropy in hydrocarbon exploration has been shown to be significant (e.g. Tompkins, 2004Tompkins, , 2005Hoversten et al 2006;Lu and Xia 2007). The overburden anisotropy has been shown to produce larger effects than anisotropy at the reservoir level (e.g., Tompkins, 2005, Li andDai, 2011).…”

“…Shale is the most common rock where anisotropy (both acoustic and electric) is generated at the micro-scale (although layered shalesand could have macro-scale anisotropy). Hoversten et al (2006) presented a case where a highly anisotropic shale layer (R vert /R horz ~ 40) had been mistaken for a hydrocarbon bearing sand. In comparison, the vertical resistivity of many hydrocarbon-saturated sands can be on the order of 30 m and in some cases lower, placing them in the same range as anisotropic shale.…”

CSEM technology as a value driver for hydrocarbon exploration

“…Serious efforts to develop the concept in the 1980's came to an abrupt end with the sudden fall in oil prices simultaneously with successful implementation of 3D seismic data. However, during the past few years we have seen an increasing focus on the use of CSEM technology for direct hydrocarbon detection Ellingsrud et al, 2002;Røsten et al, 2003) and recently, a number of success stories have been published (Choo et al, 2006;Hoversten et al, 2006;Smit et al, 2006).…”

Identification of subsurface structures using electromagnetic data and shape priors

“…The main aim with the research presented in this paper is to develop a computationally efficient inversion methodology for CSEM data that is able to preserve prior information about geological strata, and we will therefore apply a model-based representation (see, e.g., [2][3][4][5][6][7][8][9]) of the unknown electric conductivity field. Alternatively, a pixel-based representation (see, e.g., [10][11][12][13]) could have been used, although the tendency for smoothing out the resulting conductivity field makes it less attractive.…”