Mathematical Modeling of the Differential Sticking Coefficient of Clay Drilling Fluids

The main objective of this work is to propose a mathematical model for the differential sticking coefficient of clayey drilling fluids with a lubricant as an additive and evaluate the influence of differential pressure and lubricant content on filter cake thickness and permeability. Tests were carried out on fluids composed of water and 4.86% of active bentonite clay prepared in Hamilton Beach agitators at a high rotation speed (17000 rpm) for 20 minutes. After a 24-hour time-out in a closed container, lubricants were added to the fluids at different levels. To obtain the differential sticking coefficient (DSC), and the filter cake, a differential sticking tester by Fann with a spherical torque plate was used, and the filter cake thickness was determined in an extensometer. The setting time, differential pressure, and lubricant content were defined as the input variables (independent variables) to the DSC mathematical model. The differential pressure and lubricant rate were the independent variables to the mathematical model of filter cake thickness (FCT) and permeability (K), which varied according to a factorial planning, was known as a second order model. The experimental data regression was performed utilizing Statistic software, version 7.0. The results clearly showed that it was possible to obtain a statistically meaningful and predictive mathematical model for DSC. It was also observed that the increase in the lubricant content was responsible for a DSC value reduction due to the fact that the lubricant was a dispersing agent reducing the filtrate volume and the filter cake thickness, and thereby decreasing the sticking risk due to differential pressure. Finally, from the analysis of point values and response surfaces for FCT and K, it was possible to observe tendencies that made clear that the differential pressure and lubricant content influenced filter cake properties

Study of the phenomenon of differential arrest and thermal stability of clay fluids.

Devido aos avanços tecnológicos, as perfurações de poços de petróleo a grandes profundidades são cada vez mais constantes e, como consequência, maiores problemas de perfuração são encontrados. A prisão diferencial, fenômeno que ocorre quando a coluna de perfuração fica presa, sem rotação, impedindo o seu movimento, mas com o fluido de perfuração circulando normalmente, é um dos problemas observados. Outro problema encontrado em perfurações de poços profundos é o intervalo de temperatura. A medida que aumenta a profundidade do poço, a temperatura na parte inferior do poço aumenta, isto acarreta em um efeito negativo no avanço da perfuração de um poço, pois as propriedades dos fluidos são afetadas pela temperatura e o seu comportamento é imprevisível e, de fato, ainda não totalmente compreendido. Desta forma, desenvolver uma formulação que suporte adequadamente ambientes de elevada temperatura e com menores riscos de prisão de tubos é desafiador, principalmente porque pouca atenção é dada ao projeto adequado de fluidos. Assim, este trabalho teve como objetivo geral avaliar a estabilidade térmica e o desempenho de fluidos argilosos sob elevadas temperaturas e condições de prisão diferencial. Para tanto, foram feitos estudos de propriedades reológicas, filtração, pH, densidade, lubricidade e prisão diferencial. Os resultados evidenciaram que: para os fluidos preparados apenas com argila, a concentração de argila e a temperatura são fatores determinantes para alteração das propriedades reológicas e de filtração dos fluidos, pois estes alteram o grau de flocuiação e dispersão das argilas e, devido a ausência da característica lubrificante dos fluidos, o fator primordial para redução do risco de prisão diferencial, são as propriedades de filtração (VF, ER e K). Para os fluidos argilosos aditivados com polímeros e lubrificante, os ensaios de DSC não indicam, de forma real, a temperatura de degradação dos fluidos, sendo estes estáveis termicamente a 93°C e, fluidos com característica lubrificante garantem menores riscos de prisão diferencial, pois a lubricidade, neste caso, é o fator de maior influência.Due to technological advances, the oil wells drilling at great depths are increasingly constant and, consequently, higher drilling problems are encountered. The differential sticking, phenomenon that occurs when the drill string is stuck, without rotation, preventing the movement, but with the drilling fluid circulating normally, it is one of the problems observed. Another problem encountered in drilling deep wells is the temperature range. As the depth of the well increases, the temperature at the underside of the well increases, this causes a negative effect on the progress of drilling well, because the fluid properties are affected by the temperature and its behavior is unpredictable and, in fact , not yet fully understood. Thus, to develop a formulation that adequately support ambient of higher temperatures and lower risks of prison tubes is challenging, mainly because little attention is given to the proper design of fluids. Thus, this study aimed to evaluate the thermal stability and the performance of clay fluids under high temperatures and differential sticking conditions. Therefore, studies were made of Theological properties, filtration, pH, density, lubricity and differential sticking. The results showed that: for fluids prepared only with clay, the clay concentration and temperature are key factors to change of theological properties and filtration of fluids, because they alter the degree of flocculation and dispersion of clays and, due to the absence of lubricating characteristic of the fluids, the primordial factor in reducing the risk of differential sticking are the filtration of properties (VF, ER, and K). For clay fluids additivated with polymers, lubricant, the DSC tests do not indicate, in a real way, the degradation temperature of the fluids, which are thermally stable at 93°C and, fluids with lubricant characteristics ensure a lower risk of the differential sticking, because the lubricity, in this case, is the most influential factor

INFLUENCE OF THERMAL AGING IN DIFFERENTIAL STICKING PROPERTIES OF THE DRILLING FLUIDS WITH CLAY

This work has the aim to evaluate the influence of thermal aging and filtration properties in the differential sticking of the clay fluids. Clay fluids with dispersant additives tested at room temperature and after thermal aging are studied. Drilling fluids were submitted to thermal aging for 16 hours in a Roller Oven at 93,3°C (200°F). Fluid loss (FL) and the differential sticking coefficient (DSC) in a Fann differential sticking tester under a pressure of 477.5 psi are determined. The cake thickness (CT) is determined by an extensometer. It is concluded according to the results obtained that the thermal aging has significant influence in fluid losses and in the cake thickness of the studied fluids. Moreover, it is shown that the risk of arrest by differential pressure fluid is not influenced by thermal aging at 93.3°C