Project 6: Marine CSEM method as a Direct Hydrocarbon Indicator Name & position: Ali Moradi Tehrani , PhD Department: Geotechnology Section: Applied Geophysics and Petrophysics Start: October 1, 2005 Proposal CTG: Prof.dr. P.M. van den Berg (TNW/EWI) CTG: Dr. E.C. Slob (CiTG) Until now, hydrocarbon exploration is carried out with the seismic method, exploiting sound waves. Only recently first trials were undertaken to explore for hydrocarbons using the low frequency electromagnetic induction (EMI) technique. We propose to upgrade those initial trials by developing a fast and accurate inversion strategy to improve the detectability of the method. A standard field survey is to drop several receiver antennas to the ocean bottom and then use a vessel to move a transmitter antenna across the area where the receiver antennas are placed. The data is then processed to exploit the time signature behaviour of the electric field with and without the presence of a thin high-resistivity layer. Unfortunately, the resistivity contrast in a hydrocarbon-bearing layer is not so large to be able to rely only on this anomaly of the electric field. The standard measurement technique uses two horizontal electric dipoles and two perpendicular vertical coils to measure the horizontal electric and magnetic field vectors. This is sufficient for full downward propagation of the electromagnetic field to the target level. The Delft scheme of diffusive field decomposition and downward continuation to improve the accuracy of resistivity estimates at depth is unique and very well suited for such a ‘complete’ vector data set. The main challenge for this new technique is to reduce the total acquisition area covered with the seismic method to the high-prospect areas, since the seismic method is relatively expensive, while the EM method is very cheap. A sensitivity analysis is performed to investigate the necessity of 3D-investigations. The reliability of the EM technique should be dramatically enhanced to achieve that goal. The purpose of the proposed study is to bring added value to the seismic method. Another advantage of the EM acquisition method is the fact that the receiver antennas are placed on the ocean bottom and can therefore be easily used in time-lapse mode. This enables us to also study the production effects once the receiver antennas are placed above a producing hydrocarbon reservoir. Our expertise in time-lapse seismic imaging and characterization will facilitate to use similar techniques using the diffusive EM fields. Within the Centre for Technical Geoscience (CTG), electrical engineers, physicists, mathematicians and earth scientists collaborate on various Geoscience topics from forward modelling, acquisition, processing and imaging and inversion to interpretation and characterization. At present, the applicants collaborate in GPR research. Here they propose to use their expertise in electromagnetic imaging and inversion (EMII) to collaborate on low frequency ocean bottom electromagnetic data inversion for hydrocarbon exploration. The project will result in a working inversion software tool for the standard acquisition geometries used in present surveys. It will also evaluate the present acquisition design in terms of optimal hydrocarbon layer detection abilities of the method. It is expected that the successful termination of this project will result in the generation of large-scale industry contributions to further research. Initial contacts with two companies resulted in enthusiastic responses and great company interest once our method has proven its superiority. Test data sets will be made available once the software has been successfully tested on ‘blind modelled’ data.

We request funding for one PhD candidate and research bench fee for computers, software, etc.

Report 2005 Abstract Until now, hydrocarbon exploration is carried out with the seismic method, exploiting sound waves. Only recently first trials were undertaken to explore for hydrocarbons using the low frequency electromagnetic induction (EMI) technique. This project aims at improving the diffusive electromagnetic method for marine oil exploration and monitoring of oil production. Two main issues are addressed to achieve this goal. The first is to establish an optimal acquisition configuration and to perform a sensitivity analysis is performed to investigate the necessity of 3D-investigations. The second is to remove all sea surface related effects from the data enabling successful application of this method in shallow seas. Introduction The principal geophysical tool for hydrocarbon exploration and monitoring the subsurface processes due to production is the seismic method. eismic acquisition is relatively expensive for mere exploration and alternative methods have a good opportunity to be commercially used when they present an almost direct hydrocarbon indication in the measurement. In recent years marine controlled source electromagnetic methods is significantly developed in methodology and instrumentation as a complimentary method to the seismic. Hence, one of the main challenges for this new technique is to reduce the total acquisition area covered with the seismic method to the high-prospect areas. Another advantage of the EM acquisition method is the fact that the receiver antennas are placed on the ocean bottom and can therefore be easily used in time-lapse mode. This enables us to also study the production effects once the receiver antennas are placed above a producing hydrocarbon reservoir. Low frequency domain controlled source electromagnetic sounding which is, so-called seabed logging is the method to approach our goals. The main idea is to measure high resistive layers. Hydrocarbon reservoirs typically have a resistivity that is sometimes up to two times higher than a water reservoir and also surrounding lithology such as shale and mudrock and this is sufficient to support EM up-going scattered field to be recorded by receivers located on the seabed. In this research the interactions with the sea surface when using marine controlled source system in shallow water is discussed. Due to the sea surface problem most of the recent activities are only focused on deep water prospects. Even in geophysical literature a very little attention is paid to this problem. The problem commences when we are faced with strong reflected EM energy comes back from sea surface to the seabed where receivers are placed. Furthermore a sensitivity analysis must be performed for acquisition geometry optimization. The reliability of the EM technique should be dramatically enhanced to achieve this goal. The result of modelling low frequency ocean bottom electromagnetic data will be presented in working acquisition optimization software tool and a data processing scheme for eliminating the sea surface effects. The project is started from the first of October, 2005. Results in 2005 Basic theory and relationships in diffusive electromagnetic field has been reviewed. Project planning has been done partly. As a first step in developing the modeling package, the electromagnetic Green’s tensors for a multilayer inhomogeneous medium are being derived. Research plan for 2006 The derivation of the electromagnetic Green’s tensors for a multilayer inhomogeneous medium will be completed. Integral equations will be solved and diffusive electromagnetic field will be computed. Sensitivity analysis will be performed for single and multiple high-resistivity subsurface objects. The theory for eliminating sea surface effects will be formulated. Coursework in 2005

Tg030 - Introduction to reservoir engineering (Monday – Friday 12 December – 16 December 2005) Supervised MSc thesis NA Publications in 2005 None Visibility The financial support for this project has lead to collaboration with Wim Mulder (part-time professor in Applied Geophysics Section,TUDelft, and part-time at Shell), which has culminated in an industry sponsored (Delphi) complementary project problem of electromagnetic methods for oil production monitoring on land. This second project will start in 2006 when a suitable candidate has been found.