A CT Scan Aided Core-flood Study of the Leak-off Process in Oil-based Drilling Fluids

Abstract

The leak-off of oil-based mud (OBM) into sandstone cores was studied both theoretically and experimentally. Simple models were used to describe the build-up of the external filter cake and the internal filtration of small particles. Then systematic static leak-off experiments were done using an innovative method where CT scans taken at time intervals were used to visualize and accurately quantify infiltration of fluids into sandstone cores. This method allowed the monitoring of the leak-off process in a way that could not be done by the traditional API filter paper press test. The composition of oil based drilling fluids was varied, to investigate the influence of various particles on the leak-off process. Scanning electron microscopy (SEM) was used to characterize the external filter cake and internal filtration. The core flow experiments were matched to the theory for linear static filtration. The results lead to new insights concerning the build of external filter cake and internal filtration. This work creates a basis for future improvement of oil-based mud, by providing a better understanding of mechanisms involved in leak-off process and its control.

CT Scan Study of the Leak-Off of Oil-Based Drilling Fluids into Saturated Media

“…-≪ .1 − 0 9 / 1 −above equations reduces to that used our earlier works for the study(Guo et al 2011, van Overveldt, 2011. Total pressure drop over the external filter cake and core is given by ∆& I IRM = ∆& R + ∆& (A2)…”

“…Recently, we reported an analysis of the leak-off of standard oil-based drilling fluid containing barite and gilsonite into dry Bentheimer sandstone cores. The study introduced an innovative method in which CT scans of the core at time intervals revealed simultaneously the build-up of the external filter cake and internal filtration (Hua et al, 2010;van Overveldt et al, 2011). This technique made it possible to investigate leak-off beyond the capabilities of standard HTHP press test with API filter paper (Aston et al, 2002;Hua et al, 2010).…”

“…The objective of this study is to examine both theoretical the leak-off of oil-based drilling fluid into cores either fully saturated with water or containing oil. The study is a detailed extension of our earlier work (van Overveldt et al, 2011) and employs similar techniques mentioned above. Calcium carbonate particles were used instead of barite and no gilsonite was added to the drilling fluid.…”