API Filtrate and Drilling Fluid Invasion: Is There Any Correlation?

Abstract

Abstract Filtrate invasion is one of the most important parameters to be controlled in a drilling fluid. Excessive filtrate invasion causes huge and, in some cases, permanent damage to the well. Among the main effects caused on a reservoir by excessive filtrate invasion are: difficulty, or sometimes impossibility, of identifying hydrocarbon reserves from logs and permeability reduction, that can turn an otherwise good well into a non commercial one. Nowadays, the invasion properties of a fluid is usually estimated by the API filtrate test. However, this procedure uses a filter paper to simulate the permeable formation, what is not realistic, since the structure of real permeable formations is quite different from the one in that "porous" medium. This work describes a simple rigsite test, very similar to the standard API filtration test, except for the fact that the filter medium is a sand bed, instead of the filter paper. A number of fluids commonly used in the oil industry were tested using both the traditional (API) and the new (BR) filtration procedures. The most important differences observed in the results are highlighted, clearly demonstrating that there is no correlation between the amount of filtrate collected from both tests.