Andrea Lovatini

Application of 3D anisotropic CSEM inversion offshore west of Greenland

CSEM can provide oil companies with information on rock resistivity before drilling a well. We present a CSEM interpretation workflow based on anisotropic 3D inversion applied to a dataset acquired offshore west of Greenland. We show how the method can give complementary information on the resistivity properties. Integrated with seismic and geological knowledge, this allows high-grading prospective leads, detection of resistivity features such as volcanics or shallow basement, and provides evidence of possible resistivity anisotropy.

3D inversion of total field mCSEM data: The Santos Basin case study

We present a marine Controlled Source Electromagnetic (mCSEM) 3D interpretation workflow based on anisotropic inversion applied to a dataset acquired in the Santos Basin offshore Brazil as part of a co-operation project between Petrobras and Schlumberger to evaluate the integration of deep reading Electromagnetic (EM) technologies into the full cycle of oil field exploration and development. The mCSEM dataset was acquired to demonstrate the improved detection and delineation of challenging EMtargets such as “smaller and deeper” hydrocarbon filled reservoir zones in complex background using 3D total field data. The project area hosting a proven reservoir was covered by a receiver grid and an orthogonal source lines grid extending beyond the receivers in the in line and cross line directions with all receivers active throughout the acquisition of both the orthogonal sets of source lines. We show that 3D inversion of the mCSEM total field data embedded in an advanced integrated workflow improves our ability to delineate hydrocarbon, their position and thickness resolution and increases our confidence about the resistivity at the reservoir(s) level. This increased resolution can provide in subsequent integrated interpretation workflows detailed information about reservoir volume distributions.

3D Velocity Model Building via Simultaneous Joint Inversion of 2D Seismic and 3D Gravity Datasets

In 2D seismic surveying the geology is often under-sampled in space. The geologic structures change in space more rapidly than what the grid sampling can capture. In modeling, tomography is used to infer perturbations in the ray trajectory and time, in order to update the velocity of the time reflections. To obtain a reliable solution, it is essential to provide the inverse solver with the most uniform information distribution in terms of areal coverage, offset and azimuth of propagation. The SJI methodology enables building a single 3D velocity model inferred by the simultaneous use of multiple 2D seismic lines of varying orientations and of a 3D non-seismic (potential field or EM) measurement. 2D seismic lines are gridded in a single 3D volume and inverted jointly with either 3D gravity or 3D EM data. While these 3D non-seismic measurements operate on their own properties for minimizing their own data misfit, the similarity criterion regularizes the 3D structure to the velocity property operated by the seismic data. This enables an advanced imaging for the 2D seismic lines. In particular, the estimation of a correct 3D tilt angle from the model enables the application of tilted-transverse isotropic (TTI) ray-tracing technology for tomography and migration.

Estimation of the Petrophysical Model via Joint Inversion of Seismic and EM datasets

Reservoir characterization objectives are to estimate the petrophysical properties of the prospective hydrocarbon traps and to reduce the uncertainty of the interpretation. In this framework, we present a workflow for petrophysical joint inversion of seismic and EM attributes to estimate the petrophysical model in terms of porosity and water saturation. This study realizes the joint inversion within the probabilistic structure provided by the Bayesian theory. The algorithm is applied to a real hydrocarbon exploration scenario to evaluate its contribution to the interpretation phase. 3D volumes of estimated porosity and saturation, show how the joint inversion of acoustic impedance and electrical resistivity can provide a quantitative description of the reservoir properties and with it a measure of uncertainty, which is consistent with the petrophysical model and observations.