Pastas de cimento para aplicação em poços de petróleo com zonas fraturadas

Abstract

Hydrocarbon deposits made up of oil and natural gas occur naturally throughout the world. Such deposits are normally contained within rocks called "reservoir rocks", usually sandstones or carbonates. These deposits exist in varying conditions of pressure, temperature and depth, from a few hundred to thousands of meters deep. During the drilling of the oil well, to reach the reservoir rocks, it is common to find areas with high permeability or naturally fractured zones, where there is the possibility that some or all of the cement or the drilling fluid used is lost, that is: penetrate the formation where the drilling and/or cementing is occurring. Such events are known in the industry as "fluid loss" and may cause several undesirable effects, among them, loss of control of the well during drilling/completion or failures in the cementation, which may even lead to loss of the well or serious accidents. Commercially, there are alternatives for the development of cement slurries with fluid loss control for the formation. However, most of these solutions have high costs and low guarantee of efficiency. Due to the reduction in the operating margins of the oil industry and the reduction of the oil price, there is a need for increasingly optimized processes, reducing costs and potential for failure. In this work, a set of statistical plans was carried out to determine the best cement paste that could be developed with materials used for fluid loss control and, among these materials, how they would behave in the loss of fluid. The studied pulp was developed with vermiculite, calcium chloride and nanosilica, studying the action of vermiculite as a reducing agent of the system. In addition to these, polystyrene sponge was also added to the slurry to act as a fluid loss controller. It was possible to obtain stable compositions with high water/cement ratio, suitable rheological properties and low densities, which were set at 12.5 lb/gal and excellent fluid loss control. Stability tests on settling showed that the pastes were stable under the proposed conditions, and the compressive strength tests showed values of the order of 10 MPa. The action of the foam contributed with the reduction of up to 97.5% of the loss of fluid to the formation, compared to other non-foamed pastes. Thus, it has been demonstrated that the foam is an agent of great utility in controlling the loss of fluid for formation.