Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Petrol ve Doğal Gaz Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2023
Tezin Dili: İngilizce
Öğrenci: MUZAFFER GÖRKEM GÖKDEMİR
Danışman: Mahmut Parlaktuna
Özet:
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.