Reservoir characterization

In the last decades, several studies on the geology of the Campos and Santos Basins have been produced, with a focus on understanding the characteristics of the pre-salt carbonate reservoirs. The motivation for these studies is related to the great economic potential of these reservoirs.

According to the National Petroleum Agency (ANP), in January 2020, for example, pre-salt production broke a record in Brazil and accounted for 66.37% of Brazilian production. For the production and exploration of the pre-salt, it is necessary to understand the heterogeneities of the carbonate deposits and how is the variability of these rocks in the oil reservoirs.

Research line 3 (RL3), entitled “Characterization and geological modelling of the Brazilian pre-salt carbonate reservoir”, aims to study the geological processes related to the development of the Brazilian pre-salt carbonate reservoirs.

The pre-salt reservoirs are found below an extensive layer of salt that can reach up to 3 km in thickness. These carbonate rocks were formed millions of years ago, during the period when the continents of South America and Africa were separating. During this geological period, oil accumulated in these carbonate rocks and the salt layer served as a sealing rock, keeping the oil trapped until today.

In this context, RL3 works on the generation of geological models, with the representation of the main heterogeneities of the reservoir, and has the following research activities:

  1. Seismic interpretation applied to stratigraphic analysis;
  2. Petrophysical and faciological analysis of the reservoir;
  3. Fault/fracture interpretation and representation in the geological model;
  4. Characterization of karst features of the reservoir;
  5. Generation of geological models of the reservoir and uncertainty analysis;

 

Why do we do it?

The pre-salt reservoirs are very complex, represented by heterogeneous carbonate rocks with distinct geological characteristics. It is essential to know how these rocks are distributed and the factors that control the quality of the reservoir.

How do we do it?

Through multiscale geological analysis (seismic, well record, core sample) and integration through multidisciplinary studies. 

What do we do?

We process and interpret seismic data (horizons and fractures) and correlate with well records and core data to generate a 3D model of the reservoir.

Elevação Artificial

The process of oil production that consists of the ascension of fluids from the well to the platform is called elevation. The elevation can be natural or artificial. The natural elevation is the process that uses the energy from the reservoir to flow the fluids to the platform. Artificial elevation, on the other hand, consists of the process that uses an external energy source, additional to the reservoir energy. Submerged Centrifugal Pumping (BCS) is one of the main artificial lifting methods used in oil production. This method is characterized by high production flow rates, installation flexibility and consists of using a multistage centrifugal pump to supply energy to the oil and lift it to the production facilities. However, some operating conditions are averse to the application of BCSs, such as fluid viscosity. Its application in heavy oil fields or with high fractions of water, in which the formation of emulsions can occur, are examples of the operation with fluids of high viscosity.

The emulsion is characterized by the presence of a dispersed fluid (dispersed phase) in another (continuous phase). The high shear and turbulence generated by the pump can promote the mixing of the phases in small drops, producing emulsions, which can be of the type oil in water (O/W) or water in oil (W/O). Depending on the dispersed phase fraction and the physical and chemical characteristics of the fluids, there is a phenomenon called continuous phase inversion. This phenomenon promotes operational instabilities in the production of oil-producing fields.

Although the presence of water is a constant in oil production, only recently has there been a greater effort by the scientific community in studies of the influence of the presence of water on phenomena related to oil production. Improving the understanding, from the physical point of view, of multiphase flows in centrifugal pumps is fundamental for the advancement of technologies that can lead to more efficient BCS system designs, aiming at the reduction of operating costs and the emission of CO2 per barrel produced.

The knowledge area dedicated to ensuring that the oil production process takes place in a safe and optimized manner is known as Flow Assurance. With a focus on fluid analysis related to thermal and hydraulic threats and their mitigation using equipment, chemicals and procedures, the Flow Assurance is one of the most important technical areas for marine oil production.

The injection of chemicals, such as demulsifiers, paraffin inhibitors, hydrates and inorganic precipitates, into the production system can prevent or remedy flow guarantee problems. These chemicals often in contact with other production fluids can become unstable and precipitate, causing the clogging of injection line valves, affecting oil production.

Another important point in the flow assurance area is the deposition of paraffin in ducts. Pre-salt oils contain significant amounts of saturated hydrocarbons, which are deposited on the walls of the pipeline when thermal exchange occurs, and the temperature of the appearance of crystals (TIAC) ​​is reached. In the literature, several mechanisms are proposed to study and understand the phenomenon, but some questions remain open. The paraffin deposition problem causes major losses in oil production, which may result in a decrease in production until the total stop.

The proposal for Line of Research 2 is divided into six research subprojects (SP), each with its corresponding team (teachers, researchers, students, technicians and others). They are:

  1. RL2 - SP1: Characterization of single-phase and multiphase flow within BCS;
  2. RL2 - SP2: Study of emulsions;
  3. RL2 - SP3: 1-D modelling of the characteristic curves of BCSs;
  4. RL2 - SP4: Development of automation and control techniques for BCSs;
  5. RL2 - SP5: Clogging of chemical injection lines;
  6. RL2 - SP6: Flow assurance on underwater lines;

Why do we do it?

We believe that by thinking differently, we can improve the physical understanding of multiphase flows and advance technologies in the areas of Artificial Lift and Flow Assurance.

How do we do it?

We identified the main hypotheses that describe the phenomena and designed controlled experiments to develop phenomenological and numerical models that represent the behaviour of real oil production.

What do we do?

We derive analyzes and understandings based on experiments on Artificial Lift and Flow Assurance and propose practical recommendations supported by key performance indicators.

Reservoir Management

Developing and managing oil reserves in the Brazilian pre-salt are complex processes. There are many technological challenges related to the water depth, the lithostatic pressure and the thick layer of salt. Additional challenges arise from the different heterogeneities of the reservoir at various scales, which govern the fluid flow in the reservoir.

Besides, an important limitation to oil production in these reservoirs is often related to the high production of associated gas rich in CO2. In this context, the use of advanced oil recovery methods (IOR), such as alternating gas and water injection (WAG-CO2), is an attractive solution, both in terms of reservoir and logistics, due to its potential to increase oil recovery and safely dispose of CO2. However, the characterization of reservoirs in these contexts is a difficult process, dominated by a high degree of uncertainty and characterized by complex models with very high simulation times.

For this reason, the use of new digital field technologies appears as a promising and cutting-edge solution for optimizing production. Examples of digital initiatives include smart wells, intelligent control of oil fields, real-time data analysis and processing using machine learning methods, hardware acceleration and information visualization techniques. This technology may incur additional investments, but it adds important operational flexibility to reservoir management. However, the use of this technology is still emerging in the oil industry, which means that further research is needed to optimize its use and maximize the value of such an investment.

Faced with these challenges, RL1 was proposed with the objective of developing methodologies to improve the decision-making and optimization processes related to the development and management of the Brazilian pre-salt oil reserves. The research developed by RL1 follows the concept of development and management of closed-loop oil fields (CLFDM), as illustrated in the image below.

 

Desenvolvimento e gerenciamento dos campos de petróleo em malha fechada (Schiozer et al., 2019).

Why do we do it?

The development and management of oil reserves in Brazilian pre-salt reservoirs are complex processes. The prediction of fluid flows in the reservoir is extremely challenging due to the different heterogeneities in the different scales and complex composition fluids. Uncertainties are always present during high investment decision processes. 

How do we do it?

Using numerical reservoir simulations, data-based methods, machine learning, advanced optimization techniques, information visualization and hardware acceleration.

What do we do?

We developed methodologies to improve the decision-making and optimization processes related to the development and management of oil reservoirs in the Brazilian pre-salt.

Currently, RL1 develops researches in five main areas, called Activities (AT):

  1. AT1: Reservoir characterization and representation in simulation models;
  2. AT2: Production optimization and decision-making under uncertainty;
  3. AT3: Simulation of oil recovery methods;
  4. AT4: Simulation and visualization of models;
  5. AT5: Integration of reservoirs with production systems;