Detecting hydrocarbon reservoirs from CSEM data in complex settings: Application to deepwater Sabah, Malaysia

Abstract

Controlled-source electromagnetic ͑CSEM͒ field surveys offer a geophysical method to discriminate between high and low hydrocarbon saturations in a potential reservoir. However, the same geological processes that create the possible hydrocarbon reservoir may also create topography and nearsurface variations of resistivity ͑e.g., shallow gas or hydrates͒ that can complicate the interpretation of CSEM data. In this paper, we discuss the interpretation of such data over a thrust belt prospect in deepwater Sabah, Malaysia. We show that detailed modeling of the key scenarios can help us understand the contributions of topography, near-surface hydrates, and possible hydrocarbons at reservoir depth. Complexity at the surface and at depth requires a 3D electromagnetic modeling code that can handle realistic ten-million-cell models. This has been achieved by using an iterative solver based on a multigrid preconditioner, finite-difference approach with frequency-dependent grid adaptation.

Resistivity imaging with controlled-source electromagnetic data: depth and data weighting

“…CSEM data are used in the oil and gas industry to detect hydrocarbons because they are sensitive to thin resistive horizontal layers [1,2,3]. The physical explanation is that the highly resistive layers strongly modify the current lines emitted by the horizontal electric dipole [4].…”

Controlled-source electromagnetics for reservoir monitoring on land

“…In some cases, CSEM measurements were used as the only exploration tool. In other, it complemented seismic surveys by providing an indication of the resistivity of targets identified by seismic imaging Darnet et al, 2007;MacGregor et al, 2007). This information can improve the probability of success in hydrocarbon exploration.…”

“…However, it was just after the success of a pilot CSEM experiment for detecting thin resistive hydrocarbon reservoirs located off-shore Angola , that the CSEM method received more and more attention from the oil and gas industry. Now, more than 10 years after the Angola field-test survey, the CSEM method has established its position as an exploration tool next to seismic Darnet et al, 2007;MacGregor et al, 2007).…”

“…As EM measurements enable a distinction between highly resistive bodies and their surrounding structures, the method attracted the attention of the oil industry because hydrocarbon reservoirs are far more resistive than brine-filled formations. As reported by many authors, controlled-source electromagnetic (CSEM) measurements may indicate the presence of hydrocarbons Ellingsrud et al, 2002;Amundsen et al, 2004;Carazzone et al, 2005;Srnka et al, 2006;Choo et al, 2006;Darnet et al, 2007;MacGregor et al, 2007 Marine CSEM surveys typically employ a high-powered electric source close to the seafloor to induce low-frequency EM signals that penetrate into the subsurface. An array of EM receivers placed on the seafloor records the horizontal electric and magnetic field components.…”

Parallel goal-oriented adaptive finite element modeling for 3D electromagnetic exploration

“…In the 2D case, the modeling and inversion toolkit has been successfully applied to natural resource exploration and tectonic investigation [Darnet et al, 2007, Naif et al, 2013, Du, 2014. For example, [Du, 2014] uses seismic guided EM inversion to provide valuable information on reservoir characteristics in the North Sea region.…”