Drilling fluid's filtration and mud cake build up is often cited as one of the key factors where operators observed better control of lost circulation from one well to another. Although this may sound a routine and simplistic process, it is quite complex. To understand a true synthesis of mud cake build up, one needs to study effects of mud composition, viscosity, and fluid mechanics involved, filtration permeability, and erosion and depositional factors. In addition of these factors, there are effects of time, pressure and temperature.
In this study, a synthesis of mud filtration and mud cake build up by conducting laboratory experiments is presented. The study presents results for Non-aqueous Oil Based Muds (OBM). The methodology depends on conducting Permeability Plug Testing (PPT), SEM and EDS analysis of mud filtrates and mud cakes. We present analysis in different time spans to capture time effects for tests in high pressure and temperature conditions. Other experimental variables in this work are permeability and heterogeneity of filtration medium which are implemented by using different rock disks.
A combination of SEM study of filter-cake structures with the evaluation of experimentally determined fluid loss data leads to a better understanding of the basic principles of filter-cake buildup and formation damage. The key findings from this study are the effects of filtration medium on cumulative mud filtrate loss, invasion and mud cake characterization, and its permeability. This could not be achieved by using ceramic disks traditionally used for PPT experiments. Effects of core permeability variation on mud invasion under high pressure and high temperature conditions have been illustrated.