The petrophysical analysis of core plugs and sidewall-rock samples is key to providing rock properties that are essential to reservoir performance forecasting, reservoir management, material balance calculation and multiphase flow simulation. These properties include absolute permeability, porosity, relative permeability, capillary pressure and the electrical resistivity of the rock, among others, determined at different bottomhole depths.
With this in mind, BPS offers our clients one of the largest and most comprehensive collections of petrophysical data of Brazilian basins available on the market (with data from 55 wells already available and 99 wells slated for inclusion this year, including 69 wells from the Santos and Campos basins).
Always aiming to push our data to the limit, the integration of laboratory petrophysical analysis, well log petrophysics and pressure gradient determination from data collected by wireline formation testing can provide interpretation summaries that highlight important features such as naturally fractured systems, hydraulic continuity and oil wettability in carbonate reservoirs. Check it out below!
Naturally Fractured System
The occurrence of a regional network of extensional fractures, microfractures and vugs in the pre-salt carbonate facies have been confirmed by integrating structural geologic studies and reservoir characterization using well data from different fields in the Santos Basin.
As identified by well logs, conventional cores and sidewall-rock samples, the pre-salt reservoirs show high lateral and vertical variability of permoporous properties. To understand the reservoir systems, it is essential to integrate studies of rock heterogeneities by means of laboratory petrophysical analysis of cores and sidewall-rock samples, log petrophysics and pore pressure gradient determination.
High quality fluid transmissibilities have been evaluated by petrophysical analysis and wellbore formation flow testing, primarily caused by the existing naturally fractured system of the carbonate reservoirs. A particular structural feature of the fractured system is the existence of zones of high permeability with relatively low porosity. This permoporous anomaly can be properly evaluated by the relative number of samples with permeability greater than and porosity lower than predefined reference values.
Permeability and porosity variation with depth for wells of the Lula and Sapinhoá fields are shown in the following figures, where the anomalous data is depicted in green.
This behavior has been observed for many fields in the pre-salt Santos Basin
The prevailing tectonic-sedimentary settings in the pre-salt Santos Basin created the proper conditions for the development of a naturally fractured system together with the reactivation of normal faults, which in turn provided the hydraulic interconnectivity between the deeper source rock and producing carbonate units.
This interconnectivity can be inferred by the linear relationship between static reservoir pressure and depth obtained from wireline formation tests executed in many wells of various pre-salt fields. The following graph for the well 3-BRSA-1064-RJS of the Buzios Field shows the same pressure gradient for the Barra Velha and Itapema formations above the water-oil contact, confirming the hydraulic interconnectivity in the entirety of the carbonate units.
Although the majority of the reservoirs worldwide are predominantly water wet, many limestones are wetted by oil. The identification of reservoir wettability is very important for the design of waterflooding projects.
The relative permeabilities obtained by laboratory measurements can be used for determining reservoir fluid wettability. A strong indicator of the wettability is the cross point of the oil and relative water permeability curves. If the water saturation at this point is lower than 50%, the reservoir is predominantly wetted by oil.
This feature can be seen clearly in the following graph from well 1-BRSA-976-RJS of the Sepia field in the pre-salt of Santos Basin, where the intersections of the relative permeability curves show water saturations lower than 50%.
In summary, the BPS geodatabase is completely unique, providing full digital integration of all of key elements of reservoir systems in Brazilian offshore basins at the click of a mouse. The integration of this data has led to significant improvements in reservoir management and field development for many discoveries in the pre-salt Santos Basin, among others.