Brazilian pre-salt reservoirs are mainly carbonate formations and they represent a great opportunity for research development. There is an increasing need of synthetic simulation models that reproduce these Pre-salt flow features for research development in reservoir simulation. This work presents a simulation benchmark model available as public domain data that represents Brazilian pre-salt trends and add a great opportunity to test new methodologies for reservoir development and management using numerical simulation. The work structure is divided in three steps: development of a reference model with known properties, development of a simulation model under uncertainties considering a specific date that represents the field development phase, and, elaboration of a benchmark proposal for studies related to the oil field development and production strategy selection. The reference model, treated as the real field, is a fine grid model in order to guarantee a high level of geologic details. The simulation model under uncertainties is a large scale model, a result of a development project considering an initial stage of field management. The benchmark model is based in a combination of Pre-salt characteristics and Ghawar field information given its diagenetic events and flow features close to Pre-salt. Based on the available information, several uncertainty attributes were considered in structural framework, facies, petrophysical properties, discrete fracture network. Economic and technical uncertainties were also considered. There is an increasing need of synthetic simulation models that reproduce these Pre-salt flow features for research development in reservoir simulation. This work presents a simulation benchmark model available as public domain data that represents Brazilian pre-salt trends and add a great opportunity to test new methodologies for reservoir development and management using numerical simulation. The main result of this project is achieved: the construction of a reference model and the construction of a simulation model under uncertainties assuming the well log information from three wells. This work provides a great contribution for further research development in reservoirs with geologic and dynamic pre-salt trends.

The significant oil reserves related to karst reservoirs in Brazilian pre-salt field adds new frontiers to the development of upscaling procedures to reduce time on numerical simulations. This work aims to represent karst reservoirs in reservoir simulators based on special connections between matrix and karst mediums, both modeled in different grid domains of a single porosity flow model. This representation intends to provide a good relationship between accuracy and simulation time. The concept follows the Embedded Discrete Fracture Model (EDFM) developed by Moinfar, 2013; however, this work extends the approach for karst reservoirs (Embedded Discrete Karst Model - EDKM) by adding a representative volume through grid blocks to represent karst geometries and porosity. For the extension of EDFM approach in a karst reservoir, we adapt the methodology to four stages: (a) construction of a single porosity model with two grid domains, (b) geomodeling of karst and matrix properties for the corresponding grid domain, (c) application of special connections through the conventional reservoir simulator to represent the transmissibility between matrix and karst medium, (d) calculation of transmissibility between karst and matrix medium. For a proper validation, we applied the EDKM methodology in a carbonate reservoir with mega-karst structures, which consists of non-well-connected enlarged conduits and above 300 mm of aperture. The reference model was a refined grid with karst features explicitly combined with matrix facies, including coquinas interbedded with mudstones and shales. The grid block of the reference model measures approximately 10 × 10 × 1 meters. For the simulation model, the matrix grid domain has a grid block size of approximately 100 × 100 × 5 meters. The karst grid domain had the same block size as the refined grid. Flow in the individual karst grid domain or matrix grid domain is governed by Darcy's equation, implicitly solved by simulator. However, the transmissibility for the special connections between karst and matrix blocks is calculated as a function of open area to flow, matrix permeability and block center distance. The matrix properties were upscaled through conventional analytical methods. The results show that EDKM had a considerable performance regarding a dynamic matching response with reference model, within a reduced simulation time while maintaining a higher dynamic resolution in the karst grid domain without using an unconstructed grid. This work aims to contribute to the extension of EDFM approach for karst reservoirs, which can be applied to commercial finite-difference reservoir simulators and it presents itself as a solution to reduce simulation time without disregarding the explicit representation of karst features in structured grids.

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Simulation of coupled subsurface (reservoir) and surface (network) systems is a challenging problem and can become a daunting task if one considers computationally intensive multi-reservoir models and realistic surface network facilities. Accurate production forecast is especially important in long-term field development plans. Integration of production systems, including reservoir, wellbore and surface facilities can be done using separate simulators (explicit) or in a seamless fashion by creating a large scale model (fully implicit) that can take into account all of the individual components in a single software. Unlike the implicit formulation, the explicit method is very flexible, allowing the integration of commercial-of-the-shelf simulators. However, as a drawback, it can yield inaccurate and oscillatory solutions. In this work, a new framework for mitigating explicit coupling instabilities (oscillations) is developed by recasting the problem in a control setting. Results from this work allow fast turn arounds in large-scale simulation of coupled surface-subsurface models. Explicit coupling can present error and consequently oscillation that can grow unmanageably throughout the simulation, because the IPR curve and operating point flow rate (q_OP) exchanged at the beginning of a time step between reservoir simulator and coupling program, may not be representative for the entire coupling interval. In order to mitigate the numerical oscillations, a feedback control system, namely a PID (i.e., proportional, integral and derivative) controller is applied. The PID controller, with parameters (K_C,τ_I,τ_D) tuned manually for a group of well settings, adjusts the IPR curves generated by the reservoir simulator so that the error between the bottom-hole pressure calculated by the reservoir simulator (BHP_RS) and the bottom-hole pressure obtained in the operating point (BHP_OP) is minimal. In this case, a corrected value of the operating flow rate (q_OP) is obtained. The new methodology was tested in a synthetic numerical model (UNISIM-I-D) based on Namorado field (Campos Basin-Brazil), which is comprised by 36,739 active cells and 20 satellite wells (7 injectors and 13 producers). The results indicate that the PID control indeed reduce the rate and pressure oscillations as expected by a more theoretical control point of view, and outperforms the base scenario, which represents the network system of producer wells by proper pressure drop tables.