Julie Svay

4D-repeatability of Reservoir Illumination - New Quality Indicators for Marine Acquisition

A target-oriented approach is developed to provide support for in-fill and re-shoot decisions during time-lapse (4D) marine seismic acquisitions. Repeatability quality of surveys positioning is determined from their respective illumination on selected reservoir horizons. Quality control of seismic repeatability is carried out from processing standpoint, through the check of 4D differences in target illumination fold and shifts in reflection-points. Corresponding support to re-shoot decisions is provided onboard from a dedicated indicator. It is defined as the similarity between time-lapse illumination of individual shots or navigation lines, evaluated from an adapted image registration metric. This indicator provides a user-friendly tool to qualify the acquisition, or identify and rank any re-shoot options. Evaluation of 4D mismatches at target depth enables to derive re-shoot decisions driven from the repeatability of reservoir illumination. At the end of acquisition, monitor data are delivered that have been validated in terms of seismic illumination repeatability with respect to base data.

The seismic horizontal borehole problem: A mixed BEM-FEM-model approach in the frequency domain

A hybrid method is developed in order to model seismic experiments performed in the specific configuration of horizontal boreholes. This method is based on a subdomain analysis which allows to couple together heterogeneous domains (fluid borehole, steel casing and layered soil) using virtual works, each domain is provided with a kinematically or geometrically appropriate model: the casing is handled with a thick cylindrical shell model, while fluid and soils are handled with boundary integral equations allowing to disregard their unbounded nature. A surfacic formulation of the problem is then obtained, which is further reduced to a lineic formulation using Fourier transform under the assumption of invariant media along the borehole axis. Numerical simulations make restitution of a tube wave guided along the borehole. Influences of the casing and a plane interface between two layers in the soil are also evaluated.