Estudo da perda de carga e do escoamento de suspensões de materiais utilizados no combate à perda de circulação em fraturas

Abstract

The loss of circulation is a major challenge faced during the drilling of oil wells. This phenomenon consists in the loss of the drilling fluid through pores or fractures present in the formations to be drilled. The most used treatment to combat the loss of circulation is the use of lost circulation materials and wellbore strengthening materials. In this work, an experimental and theoretical study was carried out with the objective of analyzing the flow of suspensions and the pressure drop in fractures. Another objective of this study was to evaluate the influence of factors such as flow rate, concentration and particle size in the flow of suspensions and in the efficiency of materials used to combat the loss of circulation. The experimental equipment used was a physical simulator whose objective is to describe the flow of suspensions in fractures with openings of 2 mm, 5 mm and 10 mm and 1.5 m of length. Suspensions containing calcium carbonate flake-based materials in laminar form with different concentrations and particle size distributions were studied. The fluids were characterized from rheological tests and density and particle size distribution. For the systems studied, data on the flow rate of the suspensions and the pressure drop were recorded as a function of time. Two methodologies were proposed to correlate the pressure drop and flow rate in fractures. The prepared fluids presented a rheological behavior that can be adjusted by the Herschel-Buckley model. The suspension containing medium particles was efficient in sealing the fractures, whereas the suspensions of fine particles sealed only the fracture of 2 mm. With the increase of fine calcium carbonate concentration, the fracture of 2 mm was sealed more rapidly. No significant influence of the concentration on the pressure drop was observed on fractures of 10 mm and 5 mm. The values predicted by the mathematical models proposed to correlate the pressure drop and flow rate in the fractures were higher than the experimental values. After a linear adjustment of the models, the predicted values approached the experimental ones. With the data obtained from the rheological tests, the influence of the presence and size of the particles in the fluid rheology was observed. The simulator of flow in fractures was able to characterize the efficiency of the materials used to combat the loss of circulation. With the results obtained in the equipment, it was possible to evaluate the influence of the concentration and the size of the particles in the flow of the suspensions. These results demonstrated the effect of the pressure drop in the sealing process of the fractures. The experimental data allowed the validation of the proposed mathematical models. It was verified that in the mathematical modeling of the flow in fractures, the effect of the relative roughness of the fractures should be considered