Comparative Evaluation of Frequency and Time Domain Csem Methods for Malaysian Offshore Environments

We have undertaken an evaluation study of the capability of both frequency-domain and step-on time-domain CSEM methods for reservoir detection in both shallow-water and deepwater environments of Sarawak and Sabah in Malaysia. We selected some well sites for this evaluation study. The shallowwater well site (79 m water depth) consists of a 200 m thick reservoir of resistivity 100-200 ohm-m (Ωm) and the background resistivity is 2-5 Ωm. For the deepwater case (1137 m water depth), the well site consists of a 70 m thick reservoir of resistivity 100-200 ohm-m (Ωm) and the background resistivity is 2 Ωm. For modelling purposes, we constructed 4-layer models for each site. We used three frequencies (0.25, 0.5, 0.75Hz) for the frequencydomain method and a transient time window of 250s for the stepon time-domain modelling. The forward modelling studies show that both methods can potentially discriminate between the reservoir and non-reservoir anomalies in 79 m water depth when the resistivity contrast is greater than 20:1. In the deepwater case, the fCSEM and tCSEM methods show similar response patterns.