Research

 

 

 

After the discovery of pre-salt, advanced recovery methods involving CO2 have been studied, since these reservoirs have a high percentage of this gas. The distance from the coast and the difficult flow of CO2 made the recovery methods with this gas make strong candidates in the pre-salt reservoirs. Thus, a crucial step in the process is to characterize the flow of oil, water and gas phases in carbonate rocks. The method known as Water Alternating Gas (WAG) alternates water and gas injection to increase the recovery factor. This is due to the fact that water travels the same path as gas inside the reservoir, displacing more oil to the producing wells. Injected gas may or may not be miscible with reservoir fluids, depending not only on the type of gas, ie hydrocarbon or CO2, but also on thermodynamic conditions. In these fields with a high percentage of CO2, it is extremely relevant to research the best form of recovery, which can be continuous injection of CO2, alternating water injection with CO2, simultaneous injection of water and CO2 and also the reinjection of the natural gas produced (hydrocarbon gas). Other miscible methods can also be researched to obtain the major factor of recovery of these fields.

 

These recovery methods have a high operational cost due to gas, which represents a large fraction of the total cost, and require gas compression and injection equipment, especially for CO2, which has a high corrosion capacity. In this alternate water and gas process, several parameters need to be optimized, among which is the relationship between injected gas and water flow rates, known as the WAG ratio. Studies have shown that there is an optimal 1: 1 ratio between flow rates under reservoir pressure and temperature conditions to maximize recovery. However, in pre-salt reservoirs, there is not enough gas available for reinjection, reducing the water / gas ratio. In addition, the fields are located in ultra-deep waters with large well spacing in heterogeneous carbonate reservoirs.

 

This will require analysis of rock, fluid-fluid and rock-fluid interactions of pre-salt reservoir samples, so that the simulation model is as close as possible to reality. Thus, it is essential to model the fluids and adjust the equations of state, study the optimal number of pseudocomponents in the compositional model, evaluate the influence of rock wettability (hysteresis in WAG), among others.

 

Among the advanced recovery techniques adopted by Petrobras for light oil bearing reservoirs, the main ones are CO2 injection, alternate water and gas injection, the use of 4D seismic for reservoir monitoring and the use of intelligent well completion.

 

From the above, research will be conducted to develop competences in carbonate reservoirs, with the objective of understanding and optimizing the advanced recovery of the most viable methods in pre-salt reservoirs, focusing on the different types of injection involving CO2. For this purpose, the different lines of research listed below may be employed, each with a specific purpose within the overall advanced recovery process.