A new technique to characterize drilling fluid filter cake

Filter cake characterization is very important in drilling and completion operations. The homogeneity of the filter cake affects the properties of filtration process such as the volume of filtrate, the thickness of filter cake, and the way to remove it. Different models were used to determine the thickness and permeability of the filter cake. These models assume that the filter cake is homogeneous. The objective of this study is to measure the filter cake thickness and permeability of water-based drilling fluids by a new approach and compare the results with previous models. A HPHT filter press was used to perform the filtration process under static conditions (225°F and 300 psi). CT (computed tomography) scan was used to measure the thickness and porosity of the filter cake. SEM was used to provide the morphology of the filter cake. Leica microscope was used to determine particle size distribution. The results obtained from the CT scan showed that the filter cake was heterogeneous and contained two layers with different properties. The average thickness of the external layer was 0.1 in., which was greater than the average thickness of the internal layer (0.06 in.). Both the porosity and permeability of the external layer were zero, while the porosity of the internal layer ranged from 10 to 20 vol. %. SEM results showed that the two layers contained large and small particles but there was a very poor sorting in the external layer, which led to zero porosity in this layer. Previous models underestimated the thickness of the filter cake by almost 50%. A new method was developed to predict the thickness and permeability of the two-layer filter cake. This method predicted the experimental data very well.