Time-Lapse CSEM Monitoring: Correlating the Anomalous Transverse Resistance with SoPhiH Maps

Abstract

The CSEM method, which is frequently used as a risk-reduction tool in hydrocarbon exploration, is finally moving to a new frontier: reservoir monitoring and surveillance. In the present work, we present a CSEM time-lapse interpretation workflow. One essential aspect of our workflow is the demonstration of the linear relationship between the anomalous transverse resistance, an attribute extracted from CSEM data inversion, and the SoPhiH attribute, which is estimated from fluid-flow simulators. Consequently, it is possible to reliably estimate SoPhiH maps from CSEM time-lapse surveys using such a relationship. We demonstrate our workflow’s effectiveness in the mature Marlim oilfield by simulating the CSEM time-lapse response after 30 and 40 years of seawater injection and detecting the remaining sweet spots in the reservoir. The Marlim reservoirs are analogous to several turbidite reservoirs worldwide, which can also be appraised with the proposed workflow. The prediction of SoPhiH maps by using CSEM data inversion can significantly improve reservoir time-lapse characterization.

New Concept Ocean-Bottom Multiphysics (OBMP) Nodes for Reservoir Monitoring

“…In the present study, we extend the findings of [3] by investigating the ability of the magnetic fields to image a 3D oil-filled reservoir and detect time-lapse changes due to fluid replacement within that reservoir. We assume that the resistivity changes are only associated with the fluid substitution within the reservoir's boundaries (Figure 3a), while the background resistivity remains unchanged.…”

“…Herein we develop the findings of [13] and demonstrate that the horizontal magnetic field components (Hx, Hy) can be effectively used for 3D appraisal studies and 4Dmonitoring applications. We conducted a time-lapse feasibility study based on the MR3D realistic turbiditic model [14] employing the horizontal magnetic components of the 4D CSEM dataset calculated by [3]. We show that the horizontal magnetic field inversion outcomes are comparable to the horizontal electric field inversions and are sensitive to map time-lapse resistivity changes associated with oil-water substitution in the studied reservoir.…”

“…Figure 5 exhibits the isopach map of the MR3D reservoir with four major thick northwest-southeast trending turbidite lobes (A-D in Figure 5) that comprise the main oil-producing zones of the Marlim field [22]. [3] conducted a 4D feasibility study to assess the CSEM effectiveness in detecting resistivity changes associated with water saturation changes within the Marlim reservoir. The starting point of that study was the pre-production scenario (1991) of the MR3D model (Figure 3b).…”

“…We then conducted unconstrained 3D quasi-Newton BFGS anisotropic inversions [25] of the horizontal magnetic data (Hx-Hy) for the 2021 and 2031 datasets. To compare with the electric data (Ex-Ey) inversions results [3], we duplicated the inversion parametrization for both cases: the L1 smoothness norm utilized for the logarithm of the resistivity values, a mesh of approximately 9 million cells (see Table 1), and the identical starting model, based on previous seismic-EM integrated interpretations [3]. The inversions converged in less than 50 iterations to a satisfactory RMS target misfit of 1.…”

“…Ongoing development efforts have demonstrated the potential to enhance cost-effective deep-water reservoir-monitoring applications. Indeed, several pioneering feasibility studies (e.g., [1][2][3]) have revealed that time-lapse (4D) CSEM can play a role in improving our knowledge of the reservoir structure, fluid flow, and fluid saturation changes when appropriate acquisition and advanced integrated interpretation workflows are applied.…”