Feasibility analysis of surface-to-reservoir electromagnetics for waterflood monitoring

Summary We analyze, by means of a synthetic model, the feasibility of detecting the electromagnetic (EM) field variations related to waterflood in a large Saudi Arabian Jurassic reservoir. We utilize a 3D structural reservoir model and derive the geoelectric parameters from careful analysis of well logs acquired at the Saudi Aramco Technology Test Site. The resistivity variations as a result of water flooding are derived using characteristic parameters and injection water salinity of the field. We model a geometry consisting of a radial surface galvanic source and four EM receivers located at the reservoir level. The full EM field is modeled in the time domain and the horizontal and vertical electric field (Ex and Ez) and horizontal crossline magnetic field (dBy/dt) components are interpreted and analyzed. Results indicate that all the modeled fields show substantial variations as a result of water saturation changes with field strength values above the noise level expected for EM sensors. The results will be validated next by modeling more complex and realistic 3D patterns of water saturation in the reservoir, as derived directly from reservoir simulation. Given that one of the modeled components is the vertical electric field, the electrical anisotropy of the overburden is expected to play a significant role in the response and will be taken into consideration in the next round of modeling. Modeling results also suggest that the type of borehole EM sensors currently available in the industry may not be adequate for surface-to-reservoir EM applications

Méthode d’inversion conjointe de données sismiques représentées sur des échelles de temps différentes

The invention is a method of constructing an image representative of a heterogeneous medium by a procedure of joint inversion of seismic data represented on different time scales having an application for underground reservoir exploration. Sequential inversion of the seismic data is performed so as to determine a first model from the seismic data expressed in a first time scale, and a second model from the seismic data expressed in the second time scale. A scale factor t1(t0) allowing synthetic data described in a first time scale to be expressed in a second time scale is defined by a differential equation relating the traveltime variations of a seismic wave to the models resulting from the sequential inversion. Finally, joint inversion wherein a cost function using the scale factor is minimized is carried out so as to evaluate a difference between the synthetic data and the seismic data expressed in another time scale.Méthode d'inversion conjointe de données sismiques représentées sur des échelles de temps différentes-Méthode pour construire une image représen-tative d'un milieu hétérogène, au moyen d'une procédure d'inversion conjointe de données sismiques représen-tées sur des échelles de temps différentes.-On réalise une inversion séquentielle des données sismiques, pour déterminer un premier modèle à partir des données sismiques exprimées dans une première échelle de temps, et un second modèle, à partir des don-nées sismiques exprimées dans la seconde échelle de temps. Puis, on définit un facteur d'échelle t 1 (t 0) permet-tant d'exprimer des données synthétiques décrites dans une première échelle de temps t 0 , dans une seconde échelle de temps t 1 , au moyen d'une équation différen-tielle reliant les variations de temps de trajet d'une onde sismique aux modèles issus de l'inversion séquentielle. Enfin, on réalise l'inversion conjointe, dans laquelle on minimise une fonction coût utilisant le facteur d'échelle de façon à évaluer un écart entre les données synthéti-ques et les données sismiques exprimées dans une autre échelle de temps.-Application à l'exploration de gisement souterrain

Towards Efficient I/O Scheduling for Collaborative Multi-Level Checkpointing

International audienceEfficient checkpointing of distributed data structures periodically at key moments during runtime is a recurring fundamental pattern in a large number of uses cases: fault tolerance based on checkpoint-restart, in-situ or post-analytics, reproducibility, adjoint computations, etc. In this context, multilevel checkpointing is a popular technique: distributed processes can write their shard of the data independently to fast local storage tiers, then flush asynchronously to a shared, slower tier of higher capacity. However, given the limited capacity of fast tiers (e.g. GPU memory) and the increasing checkpoint frequency, the processes often run out of space and need to fall back to blocking writes to the slow tiers. To mitigate this problem, compression is often applied in order to reduce the checkpoint sizes. Unfortunately, this reduction is not uniform: some processes will have spare capacity left on the fast tiers, while others still run out of space. In this paper, we study the problem of how to leverage this imbalance in order to reduce I/O overheads for multi-level checkpointing. To this end, we solve an optimization problem of how much data to send from each process that runs out of space to the processes that have spare capacity in order to minimize the amount of time spent blocking in I/O. We propose two algorithms: one based on a greedy approach and the other based on modified minimum cost flows. We evaluate our proposal using synthetic and real-life application traces. Our evaluation shows that both algorithms achieve significant improvements in checkpoint performance over traditional multilevel checkpointing