Junsheng Hou

Integration of 3D Modeling and Real-time Processing for Enhancement of Anisotropic Formation Evaluation with Borehole Multicomponent Induction Measurements

It is well known that around the world a number of oil and gas reservoirs consist of formations which are identified as resistivity/conductivity anisotropic by borehole induction tools, such as thinly laminated sand-shale or bedded sand-sand rock sequences. Therefore, resistivity-anisotropy formation properties are critical for accurately evaluating anisotropic reservoirs. For many years the logging industry has tried to use induction tools to measure both horizontal and vertical resistivities of reservoir formations. As one of the latest and most remarkable developments in the wireline induction logging domain, multicomponent induction (MCI) logging is now used to fill this requirement. Compared to conventional induction, this new logging technology is able to measure the formation anisotropy (vertical and horizontal resistivities, Rv and Rh, respectively), dip, and strike required to accurately evaluate different types of anisotropic reservoirs. When interpreting MCI data for the purpose of anisotropic formation evaluation, most cases theoretically require 3D electromagnetic (EM) forward modeling and inversion. However, experience has clearly shown that the current 3D forward modeling algorithms often fail to obtain accurate solutions in a reasonable amount of CPU processing time. Even for the most efficient algorithms, fully 3D inversion is impractical for the real-time or well-site delivery of inverted results from measurements. For fast and accurate 3D EM forward modeling, a practical 3DFD (finite difference) method based on an isotropic/transverse isotropic (TI) background is presented and used. This method has been tested by fast borehole-effect correction (BHC) and several independent 3D codes. Its practical application workflow is also proposed and tested. The timeconsuming 3D inversion is generally partitioned into a few simple and fast data processes including resolution enhancement of MCI logs for reducing shoulder-bed effects and a few low-dimensional inversions such as radially one-dimensional (R1D) inversion, which makes possible the real-time delivery of formation anisotropy (Rh and Rv), dip, and strike information. Moreover, the R1D inversion is based on a fast and rigorous multistep inversion algorithm and a fast forward modeling engine which consists of the pre-calculated MCI-response library created by using the fast 3DFD method. This novel method of integrating 3DFD numerical modeling and real-time processing technologies has been proposed and implemented for enhancing anisotropic formation evaluation. To demonstrate its capability and effectiveness, we successfully validated the method on both synthetic data and field log data sets.

Fast determination and characterization of formation resistivity anisotropy, dip, and fracture using multicomponent induction data

AbstractMulticomponent induction (MCI) logging measurements have been widely used in the past decade for determining formation resistivity anisotropy (horizontal and vertical resistivities: Rh and Rv), dip, and azimuth. Currently, almost all MCI processing and interpretation algorithms of determining Rh, Rv, dip, and azimuth are based on simplified transversely isotropic (TI) formation models. In most geologic environments, formations are layered or laminated, making the TI model a reasonable assumption. Subsurface formations usually contain different types of fractures (natural or drilling-induced), and exhibit azimuthal resistivity anisotropy in the bedding plane, which leads to formation biaxial anisotropy (BA) in the same bedding plane. (This type of media is usually called orthorhombic or orthotropic in mechanical engineering and geomechanics.) Therefore, MCI data processing based on TI models may not be valid in complex BA formations caused by fractures. MCI processing and interpretation methods bas...