Appropriate drilling fluid additives which can build effective filter cakes are key components to minimize formation damage. Today there exists no effective and quantitative technique which can assess the formation damage minimization potential of any novel drilling fluid. This study provides the methodology for such a technique, by integrating HP/HT fluid loss data, derived from standard API HP/HT filter press, with filter cake quality and filtrate penetration depth, derived by Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) techniques.

Novel nano-based drilling fluidwas made of de-ionized water, 7 wt% commercial Na-bentonite, and addition of custom made iron oxide (CM Fe3O4) nanoparticles (NP) at 0.5 wt%. Its excellent filtration characteristics were determined at elevated pressures and temperatures using a HP/HT filter press (500 psi/350°F) with ceramic discs, mimicking the formation, as filter media of k=775 mD. NMR T2 relaxation time measurements provided the pore size distribution of the ceramic discs, and a newly developed MRI technique by our team allowed direct visualization on the core-ceramic disc of the produced filter cake and filtrate penetration depth, providing insights on filtration characteristics.

Addition of 0.5 wt% Fe3O4 NP resulted in a decrease of fluid loss by 47% compared to that obtained from the base fluid (BF) without the nanoparticles. The excellent filtration characteristics were attributed to the synergistic interaction of NP with bentonite platelets producing a strong microstructure network leading to rigid and very low permeability filter cakes. Spin-spin relaxation time (T2) NMR measurements revealed different pore size distribution of the nano-enhanced drilling fluid showing its tendency to occupy the smallest pores of the filter medium (ceramic disc). MRI T2 measurements revealed the saturation profiles of the drilling fluids inside the ceramic discs, in 3-D space. This allowed the visual representation of the penetration depth of the filtrate produced in the ceramic discs of the different tested drilling fluids.

Our integrated characterization approach, gives us tools to analyze inter-particle interactions in the filter cakes at HP/HT conditions in order to explain the significant improvement in fluid loss performance of novel drilling fluids. The information gained in this study is considered to be extremely significant for deriving an effective methodology for assessing formation damage potential of any newly developed drilling fluid which can lead to more efficient and cost-effective drilling activities.

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