Parallel 3D modeling of marine controlled source electromagnetic data using survey decomposition

3D modeling of marine controlled source electromagnetic (CSEM) survey can be computational expensive because of the distributed sources and receivers that cover large areas. We propose a novel approach to achieve second/minute response time for large-scale marine CSEM modeling in a massively parallel computing environment. Different from conventional parallel methods that mostly rely on spatial domain decomposition, our approach decomposes the original data set using relations in survey configurations. We consider a large marine CSEM survey as a simple assembly of many small “atomic” problems, each of which only models one datum from a single source (S) and single receiver (R) at a single frequency (F). Each S-R-F problem is then modelled using a local mesh customized to the specific frequency and S-R geometry. Such a mesh is usually small, so the solving time is at the order of seconds or minutes if efficient and accurate direct solvers are used. The decomposition is also fine-grained and embarrassingly parallelizable, therefore inter-communication between sub-problems is minimal and a variety of parallel strategies can be used in a scalable manner. Our approach is demonstrated with a 10 ´ 10 km 3D synthetic reservoir model and a deep-towed EM system. Upon decomposition, 6912 independent sub-problems are generated; the number of cells in a local mesh ranges from 11200 to 103680 and the computing time from 5 s to 158 s. Because sub-problems do not communicate with each other, the entire problem is solved when individual problems are solved. A total computing time of less than 10 minutes for such a large survey was achieved by distributing the sub-problems over 448 cores on multiple nodes of a computer cluster.