Cristiane Richard de Miranda

Analysis of Interface Between Newtonian and Non-Newtonian Fluids Inside Annular Eccentric Tubes

In this work, flow of two adjacent fluids through annular eccentric tubes is analyzed numerically. This kind of flow is found in cementing processes of oil wells, where the cement paste pushes the drilling mud through annular space between the drilling column and the oil well wall. Both drilling mud and cement paste behave as non-Newtonian fluids, and between then a wash fluid is usually used, to avoid their contamination. The analysis of interface configuration between these fluids helps to determine contamination, and is an important tool for the process optimization. The numerical solution of the governing conservation equations is obtained via the finite volume technique and the volume of fluid method, using the Fluent software (Fluent Inc.). The effects of rheological parameters and eccentricity are investigated, for different flow rates. The results obtained show that the displacement is better when a more viscous fluid is used to push the other fluid. Also, it is observed that the interface shape is a function of flow regime and viscosities ratio. However, it is insensitive to eccentricity.Copyright

Dynamic Aspects Governing Cement-Plug Placement in Deepwater Wells

Plug cementing is still considered to be a critical operation and cases of failure eventually happen. Large annular gap and eccentricity, typical of these operations, are factors which may promote unstable flows resulting in cement slurry contamination. Deepwater conditions enhance chances of free fall, and consequently, low displacement velocities can occur in the annulus[1]. This article presents a parametric study in the role of rheological properties of fluids (drilling fluid, spacers and cements slurries), string rotation, flow rates (including free-fall effects, where due the differences between density of the fluids the injection flow rate is different of return flow rate) in the displacement quality of cement plugs. Analyses are based on 2 different simulation tools. Conventional cement pumping softwares define flow rate profiles at annulus entrance, accounting for free fall effects and CFD simulation to define interface propagation and contamination levels. The main issues addressed by the simulations are how to optimize density and rheology hierarchy which minimizes contamination and avoids channeling The compilation of simulation results in useful guidelines and procedures for displacing cement plugs in vertical inclined and horizontal offshore wells.

Durability of Lightweight Slurries for Oilwell Cementing

In a deepwater environment, unconsolidated formations at seabed and naturally fractured carbonates at reservoir zones with high permeability are commonly found. In this context, the use of lightweight slurries is necessary to effectively cementing these formations, in order to mitigate slurry losses to the formations and to prevent their fracture. This work investigates the mechanical properties and durability of high performance lightweight slurries to be used in this environment. The mixtures were formulated within the framework of the Compressible Packing Model and were extended using hollow ceramic or glass microspheres. Tests were carried out to determine the slurries apparent density, rheology, free fluid, sedimentation, fluid loss, resistance to acid attack, sorptivity and total water absorption. A mechanical characterization was performed by uniaxial and triaxial compression and splitting tensile strength tests and were correlated with the durability tests. The reference slurry, extended with bentonite, presented a 1.46 g/cm3 density and compressive strength of 3 MPa (cure at 27oC/ 2.7 days). The slurries containing glass and ceramic microspheres were slightly lighter and presented a higher mechanical performance as compared to ordinary slurry. Besides, these mixtures presented a higher resistance to acid attacks and lower sorptivity, especially the lightweight slurry containing ceramic microspheres.

Influence of Short Polypropylene Fibers on the Toughness of High Performance Cement Slurries

In oil wells, one of the goals of the cement sheath is the hydraulic seal. Generally, cement pastes, which are adopted in cementing operations, exhibit brittle fracture when subjected to tensile stresses. This behavior can compromise the hydraulic seal promoted through the sheath. One way to mitigate this problem is the use of slurries with more deformability. In this context, this work aims the determination of the toughness of high performance cement slurries reinforced by different volume fractions (0.50% and 0.75%) of short polypropylene fibers (6mm long). The influence of fiber addition in the rheological behavior, free fluid, density, stability and unconfined compression of the slurries was also determined. The obtained results indicated an increase in the yield strength and a reduction in the spreading of the reference mix with the increase of the fiber volume fraction. The free fluid, density and stability behavior of the reinforced slurries were similar to that of the control mix. An expressive change in the fracture behavior of the brittle matrix was observed in both mechanical tests carried out. Under uniaxial compression loads, although the ascending branch of the stress-strain curve did not show expressive differences with the fiber reinforcement (only minor modifications in the peak load), the descending branches were significantly modified with the reinforced mixes presenting a smooth post-cracking behavior. The greatest benefit provided by the fibers was observed, however, in the bending tests. Both, the maximum post-cracking strength and bending toughness, were significantly augmented with the increase of the fiber volume fraction.Copyright

Liquid Displacement Through Tube-Annular Transition Region Inside Oil Wells

In this work, a numerical simulation of three adjacent fluids flowing through a tube followed by an annular axi-symmetric channel is performed. This analysis is motivated by the study of drilling and completion processes of oil wells, where a cement slurry pushes the drilling mud, used in the drilling process to lubricate the drill and to remove the produced drilling cuts. The completion process is perfect if all the drilling mud is removed, and if there is no contamination between the two fluids. To avoid contamination, a spacer fluid is usually inserted between them. Both drilling mud and cement slurry behave as non-Newtonian fluids, and the spacer fluid can be Newtonian or non-Newtonian. The analysis of flow and interface configuration between these fluids helps to determine contamination, and is an important tool for the process optimization. The numerical solution of the governing conservation equations is obtained with the Fluent software, using the finite volume technique and the volume of fluid method. The effects of rheological parameters and pumped volume of the spacer fluid are investigated. The results obtained show that the displacement is better when a more viscous spacer fluid is used. The results also shown zones of recirculation, where the drilling mud remains stagnant, decreasing the process efficiency.© 2005 ASME