Brazilian carbonate reservoir: A successful seismic time-lapse monitoring study

Abstract

Brazilian carbonate reservoirs contain huge oil-in-place volumes and are likely to have an important economic impact in global oil industry. Such carbonate reservoirs, both Albian and Aptian, are located offshore in deep water, which has an important role in development costs. In siliciclastic plays it is standard practice to use time-lapse (4D) seismic to locate wells in unswept areas, maximizing the recovery factor. However, in carbonate plays, time-lapse seismic monitoring remains challenging, with few cases of success published around the world. Carbonates differ from siliciclastic rocks in many aspects. With a varied chemical composition and complex pore connectivity, carbonates bring on a large diversity of facies, each one showing a specific seismic response. Moreover, the usually high incompressibility of the carbonate matrix reduces sensitivity to pressure and saturation changes, which are the main effects expected on a hydrocarbon field undergoing production. Considering both the economic relevance and the difficulties of using time-lapse seismic to monitor carbonate reservoirs, Petrobras created a strategic program to face this challenge, a time-lapse seismic (S4D) study of an Albian carbonate reservoir located in the Campos Basin offshore Brazil. Three legacy data were available: streamer–1987, streamer–2002, and ocean-bottom cable–2010. Extensive feasibility studies are performed as well as a meticulous prestack 4D simultaneous inversion based on the seismic data, preliminary cross-equalized to partially overcome the initial low repeatability. A multidisciplinary interpretation conducted by a team of geophysicists, geologists, and reservoir engineers finally lead to results overcoming expectations. Saturation and pressure changes are detected using P- and S-impedance attributes, consistent with production data. Results are opening perspectives for further monitoring other carbonate reservoirs, especially with new presalt Brazilian discoveries in the Campos and Santos Basins, which might have a huge economic impact.

Inelastic Compaction in High‐Porosity Limestone Monitored Using Acoustic Emissions

“…With the development of 4‐D seismic monitoring in carbonate reservoirs (Grochau et al, ; Raef et al, ), a better understanding of the in situ evolution of elastic wave velocities of porous carbonates during production or CO 2 injection is clearly needed. If a significant number of laboratory studies were dedicated to the elastic wave velocities of carbonates, a large majority were performed at ambient or low pressures and focused on the effect of depositional environments and diagenesis processes (Brigaud et al, ), porosity (Anselmetti & Eberli, ; Assefa, McCann, & Sothcott, ), microporosity (Baechle et al, ; Regnet et al, ), or pore shape (Verwer, Braaksma, & Kenter, ).…”

Microstructural Control of Physical Properties During Deformation of Porous Limestone

“…With the development of 4-D seismic monitoring of reservoirs and CO 2 injection in carbonate formations (Angerer et al, 2002;Grochau et al, 2014), a fundamental understanding of the concomitant evolution of elastic wave velocity and petrophysical attributes of carbonate rocks at in situ conditions is necessary. Such knowledge hinges on rock mechanics experiments to describe how inelastic deformation could impact rock properties in various field situations.…”

New perspectives on Solid Earth Geology from Seismic Texture to Cooperative Inversion

“…Seismic attributes are extensively used in the hydrocarbon industry. For example they routinely provide indications of 4D reservoir fluid movements in time and space 30,31 . A comprehensive table of applications for seismic attributes is provided by Roden, R., Smith, T. and Sacrey, D 32 .…”