Degrading drilling fluid filter cake using effective microorganisms

Abstract

The effective cleanup of filter cakes in long, horizontal open-hole completions can maximize an oil well’s productivity. A cleaning solution was formulated which comprised effective microorganisms and a viscoelastic surfactant in order to degrade filter cakes of water-based mud. Generally, the effectiveness of the microorganisms in degrading filter cakes is influenced by temperature and its concentration. To overcome the problem, the viscoelastic surfactant has been used to extend the application of temperature range and increase the viscosity of the cleaning solution. Laboratory studies were conducted to examine the effectiveness of the microorganisms in degrading filter cakes. The apparent viscosity of cleaning solution was measured as a function of shear rate (102.2 s and 1022 s ) and temperature (25 to 80°C). The surface tension of the cleaning solution was measured at room temperature. Static fluid loss tests were performed using the HPHT Filter Press in order to determine the effectiveness of the cleaning solution in degrading filter cake at different temperatures ranging from 100°F to 300°F. Experimental results showed that the cleaning solution could effectively degrade the filter cake. Soaking process was performed until 48 hours and it showed that at temperature 200°F and below, the pure effective microorganisms achieved the highest efficiency of filter cake degradation, i.e. 34.9%. However, at temperature 300°F, cleaning solution that contained effective microorganisms and higher concentration of viscoelastic surfactant was found to perform better. The viscoelastic surfactant succeeded in increasing the viscosity of the cleaning solution, thus enhanced the rate of degradation of filter cakes, i.e. 33.4% at 300°F. The surface tension of the cleaning solution did not change significantly at various concentrations at room temperature.