Repository logo

Effects of filtration process variables on filter cake properties and formation



Change log


Sorrentino, Gianmario 


Drilling mud is fundamental during the drilling process because it performs multiple tasks which make the perforation of the rock possible. For this reason, lost circulation, the loss of drilling mud through fractures in the formation, represents a serious issue in the oil and gas industry, since it increases the costs of the drilling process. Since fluid losses usually occur through induced fractures, a series of techniques have been developed to increase the integrity of the wellbore, stop lost circulation and allow drilling with wellbore pressure in excess of the fracture gradient. These techniques are theorized to alter the stress at the wellbore in order to make it more difficult to open or propagate the fracture. However, they do not alter the strength of the rock formation itself. For this reason, these techniques are known as wellbore strengthening. These techniques rely on using large particles which cause practical issues. Therefore, developing a wellbore strengthening mechanism that does not rely on adding large particles into the drilling fluid is needed. An alternative approach consists of using the filter cake, which naturally forms against the rock. The overbalanced pressure in the wellbore compared with the formation forces some drilling fluid into the permeable formation, and the solids present in the mud clog the pores of the formation and accumulate against the wall in a thin layer called a filter cake. In order to improve drilling mud design and produce filter cakes that can raise the wellbore integrity, more comprehensive knowledge and understanding of the mechanical properties of the filter cake are needed. The outcome of introducing filter cake formation as awellbore strengthening mechanism has the potential to impact drilling operations by overcoming the difficulties related to the conventional use of large particles and decreasing the overall material cost related to drilling fluids. An extensive research work was carried out in order to provide a better understanding of the effects of filtration variables on filter cake properties and formation. There are three main types of variables that affect filter cake properties: drilling fluid formulations, substrate properties, and operative parameters. The effect of these variables of filter cake properties was assessed through dynamic and static filtration tests. This study has proved that the filtration profile obtained from filtration tests with substrate with mean pore size larger than the mean particle size in the slurry are characterized by two regimes which take place mainly in sequence. During the first phase, the process is dominated by depth invasion of particles into the substrate leading to the formation of internal filter cake and a progressive reduction of the porosity and permeability of the substrate. The second regime was characterized by surface filtration since the pores were no longer accessible. This led to the formation of an external filter cake. The transition between these two mechanisms defined the beginning of the formation of the external filter cake and is marked by a sharp change in slope of the filtration profile. It has been observed that once the external filter cake forms, substrate mean pore size made no significant difference to external filter cake properties, whereas, filtration pressure does. The investigation of effects of tangential flow velocity on filter cake properties has shown that dynamic filtration conditions reduce the mass of external filter cake deposited, but this filtration condition promotes internal invasion of slurry particles in substrate’s pores. This study has also provided an insight of the mechanism of invasion of solid particles into the substrate pores. Numerical simulations have shown that two mechanisms are likely to contribute to blocking the substrate’s pores: pores with a diameter smaller than the mean particle size in the drilling fluid are immediately blocked, whereas larger pores are likely being clogged progressively.





Biscontin, Giovanna


cross-flow filtration, depth filtration, drilling fluids, filter cake


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Engineering and Physical Sciences Research Council (1834420)
BP through the BP International Centre for Advanced Materials (BP-ICAM) which made this research possible