Rheological Properties of Oil Based Drilling Fluids and Base Oils

Abstract

Drilling fluids for oil wells must meet a number of requirements, including maintaining formation integrity, lubricating the drill string, and transporting cuttings to the surface. In order to satisfy these needs, drilling fluids have become increasingly complex and expensive. To ensure safe and efficient drilling, it is vital for the drilling operator to be able to make a qualified choice of fluid appropriate for each individual well. API/ISO standards specify a set of tests for characterization of drilling fluids. However, fluids that are tested to have equal properties according to these standards are still observed to perform significantly different when used in the field. The aim of the full project is to provide a thorough comparison of drilling fluids in particular with respect to hole cleaning performance, in light of the issues presented above. As part of this investigation we here present results for two oil based drilling fluids, as well as for the corresponding base oil. The drilling fluids differ in composition by varying fraction of base oil, and thus density and water content. The fluids have been tested according to the API standard, and further, viscoelastic properties have been examined using an Anton Paar rheometer. The rheological test campaign includes determination of the linear viscoelastic range (LVER), viscosity and yield point, thixotropic time test, and temperature dependence of rheological parameters. Further, it is demonstrated how the rheological data may be used to interpret data from ongoing full scale flow loop experiments with the same fluids. In a more general context, the rheological test campaign of the drilling fluids is expected to make a crucial contribution for the petroleum industry in explaining observed differences in hole cleaning properties beyond what todays API/ISO industry standard provides.

Influence of the Formulated Surfactant on the Characterization of the Base Oil

“…The highest shear stress is pure base oil, followed by EBF and EB. The increase of the shear stress is significantly and gradually with the shear rate due to the increase in hydrodynamic effect which causes the increase in shear rate and shear stress [17]. Furthermore, with the presence of formulated surfactant increased the shear stress and led to higher viscosity hence causing a reduction in the interfacial tension by adsorbing the interface and screening the unfavourable interactions between the water and oil molecules.…”

pH-Responsive Drilling Fluid With High-Temperature and High-Density Performance

“…Table 1 shows that the ES value of the W/O emulsion-based drilling fluid is over 400 V even after hot rolling at temperatures of 100-150 °C, indicating excellent emulsion stability even at a low oil-to-water ratio. Normally, low oil-to-water ratio usually makes it difficult to maintain high emulsion stability and suitable rheology (Oltedal et al, 2015). The rheological properties of the O/W emulsion-based drilling fluid after reversion are similar to those of the W/O emulsion-based drilling fluid, and there is no severe demulsification or barite sag during emulsion reversion.…”

Experimental Investigation of the Rheological Behavior of an Oil-Based Drilling Fluid with Rheology Modifier and Oil Wetter Additives

“…These drilling complications could result in a stuck pipe, shale swelling or wellbore instability [ 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Although OBDF is often preferred for its superior performance in drilling a difficult well because it can easily combat these drilling complications, there is still a need for additives that are more stable physically or chemically for a longer period under extreme temperature or pressure conditions [ 37 ]. The additives play a major role in ensuring the OBDF is maintaining certain rheological and fluid loss properties to ensure its effectiveness.…”