Core Leak-off tests are commonly used to ascertain the ability of a drilling fluid to seal permeable rock under downhole conditions. Unfortunately, these tests are expensive and require a long time to set up. To monitor fluid invasion trends and to evaluate potential treatments for reducing fluid invasion on location, a simpler screening test is highly desirable. The Capillary Suction Time (CST) Test has been used since the 1970's as a fast, yet reliable, method for characterizing fluid filterability and the condition of colloidal materials in water treatment facilities and drilling fluids. For the latter, it has usually been applied to determine the state of flocculation of clay-bearing fluids and to screen potential shale inhibitors. In this work, the CST method was evaluated as a screening tool for predicting relative invasion rates of drilling fluids in permeable cores. However, the drilling fluids examined--DRILPLEX, FLOPRO, and APHRON ICS--are all designed to generate low fluid loss and give CST values that are so high that fluid invasion comes to be dominated by experimental artifacts, such as fluid evaporation. As described in this work, the CST procedure was modified so as to minimize such artifacts and permit differentiation of the fluids under investigation.

The Acoustic Bubble Spectrometer has been identified as a potential method for monitoring the size distribution of aphrons in situ, such as in an oil well drilling fluid flowline.1 Research was continued from Task 1.1 of this Project, Aphron Visualization,2 in which ABS was tested against laser light scattering (Coulter Counter) and optical (visual) imaging to determine the bubble size distribution (BSD) of the aphrons at ambient temperature and pressure. Task 2.1 continued this investigation by measuring the bubble size distribution via ABS and optical imaging at elevated pressures up to 2000 psig.