A novel Rheological and Frictional Pressure Loss equations for Non-Aqueous based Drilling Fluid Systems by considering the pressure effect

Date

2023-3-31

Author

Gökdemir, Muzaffer Görkem

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Non-aqueous conventional drilling fluid systems (NAF) are preferred due to lubricity effect, high inhibitive characteristic and temperature-rheological stability in deep formations. However their flow characteristics prone to change with pressure due to slightly compressibility nature of them. This study is designed to investigate the effect of pressure on the flow characteristics of sightly compressible drilling fluids, both experimental and theoretical work, at constant temperature conditions. Diesel and synthetic based samples are used as slightly compressible systems while water base muds are tested as incompressible drilling fluids. Rheological tests are conducted on Anton Paar MCR-302 high pressure high temperature (HPHT) rheometer. Pressure dependent constitutive stress equations are proposed and based on those rheological equations, frictional pressure loss calculation methodology is developed during the theoretical work. While a difference in pressure doesn’t affect Fluid Flow Behaviour Index (m parameter), both the Yield Stress or Point – τy and Consistency Index, (also known as K parameter), are strongly dependent on pressure change as rheological parameter analysis indicates. The hydraulic calculations obtained using the proposed constitutive stress equations were verified through real field application, where the drilling fluid system demonstrated a yield behavior with shear-thinning deformation characteristics. Field measurements were taken at two different flow rates along with pressure readings and when compared to model calculations in the annular geometry, the on-bottom pressure values were slightly overestimated with a negligible difference in absolute terms. When the oil (continuous) fraction of a non-aqueous drilling fluid system is increased in volume relative to the water (brine) phase, pressures shows more effect on the rheological parameters or stress requirements of flow for the non-aqueous based drilling fluid systems. The oil water ratio affects the level of yield stress significantly. When the o/w ratio is reduced, higher yield stress values are observed. Under the same experimental conditions, an increase in Barite content in the system results in the rise of both yield stress and consistency index. On higher mud weights, even though the relatively compressible fluid amount is decreased; the percentage increase of rheological parameters τy and K in terms of pressure is higher due to solid particle effect.

Subject Keywords

Rheology, Slightly Compressible, Drilling Fluids, Hydraulic Calculation Methodology

URI

https://hdl.handle.net/11511/103046

Collections

Graduate School of Natural and Applied Sciences, Thesis