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Cross section of a reservoir model representing trends of Pre-salt reservoir: (a) Super-K layers highlighted in red, (b) water saturation showing channeling, highlighted in darker, blue through the Super-K
Cross section of a reservoir model representing trends of Pre-salt reservoir: (a) Super-K layers highlighted in red, (b) water saturation showing channeling, highlighted in darker, blue through the Super-K.

Several new challenges in the area of reservoir characterization and simulation have emerged after Pre-salt discovery. Some of these challenges are: (a) the size of the simulation models necessary to represent the giant Pre-salt fields, which may results in very big simulation models, (b) highly heterogeneous reservoir, that is difficult to model and to represent into the simulation models and (c) complex logistic related to production facilities.

To deal with and overcome these challenges, great efforts are employed in the studies developed by UNISIM. The main focus of the applications involves: (1) use of modern reservoir characterization techniques to develop benchmark models with characteristics typical from the carbonate Pre-salt reservoirs, involving critical heterogeneities such as vugs, fractures, high permeability thin layers (Super-K), among others; (2) study of methodology to integrate the reservoir simulation with production facilities; (3) development and improvement of methodology for decision-making process applied to Pre-salt fields; (4) study of reservoir simulation techniques and upscaling methodologies to reduce the computational effort.

Typical workflow for history matching integrated with geostatistical modeling
Typical workflow for history matching integrated with geostatistical modeling

In conventional history matching procedures, petrophysical properties, such as porosity and permeability, are usually modified using multipliers. This procedure may generate models geologically inconsistent. This can be worse when changes are made regionally, because the modifications do not respect reservoir continuities. To maintain the geological consistency, respecting the spatial correlation (variogram) of petrophysical properties, the recommended procedure is to carry out the history matching process integrated to the geostatistical modeling. This procedure is usually called “Big-Loop”. However, this integration leads to a complex problem because the relationship between the input and output variables (objective function) can be highly nonlinear.

One of the main challenges is the local history matching, because it is necessary to perturb the model locally, to match individual wells and, at the same time, to maintain spatial continuity of the perturbed property. Furthermore, it is common the occurrence of cross influence, that is, modification in one region may influences wells in other regions, increasing the difficult of the problem.

The main objectives of this research line are: (1) to propose automatic workflows to integrate the history matching with geostatistical modeling; (2) to propose methodologies to condition the generation of geostatistical images based on the quality of history matching, focusing in regional perturbation for local history matching; (3) to study new methodologies to integrate history matching of naturally fractured reservoirs with reservoir characterization.

Example of History Matching and Uncertainty Reduction
Example of History Matching and Uncertainty Reduction

Production history matching is one of the most time consuming activity in the area of reservoir simulation and management whose objective is to increase the reliability of the production forecast and, consequently, increasing the exploitation efficiency. Although history matching has been extensively studied in the literature, the increase of the computational resources, in terms of software and hardware, as wells as the advances in reservoir characterization techniques, has allowing important progresses in history matching process. In this sense, a great effort has been dedicated at UNISIM in this research area in the last years, with significant results presented in dissertation and thesis, journal and conference papers and several projects sponsored by the petroleum industry and funding agencies.

It is important to highlight that the main objective of the research developed at UNISIM is to propose methodologies able to deal with practical cases, allowing the application to real fields. In general, the main research guidelines are: (1) the use of the reservoir engineering knowledge to support the analysis according to the physic of the problem; (2) the increase of the efficiency and efficacy of the process, reducing the number of simulation and improving the quality of the solutions; (3) the application of the methodology to complex cases. History matching is a multidisciplinary research area and, therefore, the main focus of the research is the integration of the process with other areas such as reservoir characterization, 4D seismic and uncertainty quantification.

There are still many challenges to be overcome in the area of history matching. Thus, the main objectives of this research line are: (1) to improve the assisted history matching process; (2) to propose and improve methodologies to integrate history matching and uncertainty analysis; (3) to study and apply new sampling and optimization methods, (4) to integrate the history matching process with the geostatistical modeling.

Example of Multiscale Characterization
Example of Multiscale Characterization

Carbonate oil reservoirs hold significant quantities of the world oil and gas reserves. The presence of multiscale heterogeneities leads to a lot of challenges for a precise formation evaluation. The construction of simulation models considering geological carbonate heterogeneities, such as fractures and vugs, remains a challenge. The study of methods for decrease simulation time consumption is also a modern challenge in the development of Brazilian Pre-salt fields.

The research line of Integration with Reservoir Characterization has the purpose of develop, apply and evaluate methodologies to represent critical heterogeneities in reservoir simulation, from geomodeling to reservoir simulation steps, based in the development of carbonate reservoirs. The main goals of this research are (1) study the impact of represent the multiscale heterogeneities in reservoir simulation, (2) study upscaling procedures in complex reservoirs, mainly fractured reservoirs, (3) apply uncertainty analysis in order to study critical parameters in the development of carbonate reservoirs and, (4) study numerical control parameters for decrease computational time consumption.

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