Estudo do desempenho de fluidos de perfuração aquosos sob condições de prisão diferencial.

Abstract

Differential sticking is a phenomenon which occurs when the drill pipe becomes stuck, without rotation, restraining its up and down movements in the well, but with the drilling fluid circulating normally. The features of the cake, the differential pressure, the deficiency on the well cleaning and an unstable well are some of the factors responsible for the imprisoning of the tubes. Various studies affirm that the fluid formulation has direct influence on the risk of differential sticking incidents. Therefore, this work aims to evaluate the performance of the drilling fluids on releasing drill pipes in differential sticking conditions. For this, there were studied clay and water based fluids, with and without polymer additives and lubricants, and polymeric fluids, before and after aging, and evaluated their rheological properties (apparent and plastic viscosities, yield strength and gel force) and filtration properties (filtrate volume and cake thickness), as well as how the lubricity and differential sticking coefficients (CPD). According to the results, it became evident, for the clay and water based fluids, that the presence of a lubricant in the fluids contributes for a smaller differential sticking coefficient, becoming possible to observe a direct relation between the lubricity and differential sticking. For the polymeric fluids, the joint action of the thin cake and the lubricant probably contributed to a reduction of the risk of differential sticking, however, no direct relation was observed between the lubricity coefficient, cake thickness and differential sticking coefficient. Besides that, it was observed that the aging of the clay and water based fluids and the polymeric fluids did not present significant rising in the differential sticking coefficient.