This reference is for an abstract only. A full paper was not submitted for this conference. Abstract Description The marine Controlled-Source Electromagnetic (CSEM) method uses electromagnetic waves to detect resistivity contrast in the subsurface which can be used to distinguish between commercial and non-commercial hydrocarbon or brine. One of the limitations of conventional CSEM is depth resolution of subsurface structures. Multicomponent data offers partial remedies to this problem while combining with seismic improves vertical resolution. A stable iterative inversion scheme that permits occam and model based inversions have been developed to investigate these problems. In this paper, joint interpretation of a gas field offshore east Malaysia using CSEM, well bore and seismic data is presented. Firstly, we carried out synthetic studies of multifrequency and multicomponent 1D occam inversion using a model derived resistivity log to determine the improvement in resolution achievable through this approach. Secondly, the similar approach is applied to a field data acquired over a gas field in east Malaysia. A model based constrained inversion approach is applied to the field data to recover improved estimates of model resistivity, not obtainable through Occam inversion. Depth determined from seismic horizons are used as a priori information in the inversion while resistivities are free parameters. Application Establish a working model for the application of the CSEM method specifically in the eastern Malaysia offshore basins. Results The inversion results of CSEM synthetic and field data is presented in detail. The results are validated using existing wellbore and seismic data. Previous work have been mostly concentrated on synthetic data, while some of the work that was presented using field data lack the validation part which requires well bore information. The synthetic studies confirm previous work by Key (2009), that broadband multicomponent inversion significantly improves model resolution. Results from the inversion of field data agree with well log but are a smoothed version. The use of seismic depth control is found to yield resistivities closer to the ground truth and is recommended. The effective sequence of operations is formulated into a workflow that can be used in deepwater exploration surveys.
This reference is for an abstract only. A full paper was not submitted for this conference. Abstract The time-domain Controlled Source Electromagnetic (tCSEM) method is emerging as a practical tool for oil and gas exploration on land and shallow marine environments (Wright et al., 2002; Ziolkowski et al., 2007). In particular, it can overcome the airwave interference problem faced by frequency-domain CSEM method in shallow water (Weiss, 2007). We have used a 1D broadband tCSEM inversion technique developed in-house. The forward problem is solved using the algorithm of Edwards (1997) while the inverse problem is solved using a variety of nonlinear parameter estimation methods (Meju, 1992, 1994). The inversion method generates either blocky sharp-boundary model or the smoothest model that fits the data recorded for different offsets and various transient times. In this work, a layered-earth resistivity model was constructed using the local borehole resistivity log and served as the test model (ground-truth). The parameters of this model were systematically varied and used to generate forward model responses enabling us to determine the effect of target depth, thickness and resistivity variations. The synthetic data for the ground-truth model were finally inverted to test the detection capability of tCSEM. The aim of our research was to evaluate the applicability of tCSEM technology in East Malaysia environment by studying the effect of target and water depth, target thickness, target resistivity variation, and target detection limits using a combined numerical modelling and inversion approach. The results of modeling and inversion studies suggest that the tCSEM method is capable of detecting hydrocarbon reservoirs in East Malaysia environment. The inversion responses become more significant when dealing with thick, strong resistivity, and shallow marine hydrocarbon target. From the case of target depth variation, the inversion responses capable to distinguish hydrocarbon target at difference depth. From this study, we capable to investigate in detail about the strength and limitation of this method in East Malaysia environment and this beneficial information can become a guideline for future feasibility study and tCSEM survey planning. Furthermore, this method also can be used as an alternative method to provide technical solution and reduce exploration risk especially in shallow marine environment.
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