(558c) A Multiparametric C.F.D. Analysis of Multiphase Annular Flows for Oil and Gas Drilling Applications

The increasing global energy demand has pushed the oil industry towards developing more intelligent and advanced methods of enhancing oil recovery even under more unfavourable technical and environmental conditions. The severity of many operational problems affecting the drilling and production of oil and gas wells is worsened by inaccessibility; hence remedial efforts must be implemented from afar [1]. One of these problems is ensuring efficient removal of formation rock cuttings with a suitable fluid, whose rheology is often complicated. Furthermore, pressure losses along the annular geometry involved, and decreased Rates of Penetration (ROP) due to accumulated drill cuttings downhole, constitute significant portions of the total energy to be supplied [2]. Thus, the application of sophisticated modelling techniques with credible elucidation of the phase distributions (solids, liquids and gas) [3] and prevalent flow regimes becomes essential, if adequate and economic design of a drilling program is desired [4].

The advent of Computational Fluid Dynamics (CFD) and the growth in the available computational power to support it have provided an unprecedented opportunity to simulate and understand complex real flows especially when experimental methods may be too demanding [3]. The application of CFD for the analysis, design and optimisation of drilling programs [5] has mostly focused on vertical and concentric annular geometries, with few studies focusing on the intricacies that evolve due to hole inclination and eccentric geometric configurations [6]. Another complication characterising the modelling process is the occurrence of multiple phases in the flow domain, which requires robust multiphase closure equations and appropriate fluid-particle tracking models to be incorporated with the principal flow equations [7]; thus, enhancing solvability and accurate prediction of the drilling variables of interest.

The choice of the multiphase flow tracking scheme in turn significantly depends on the governing particle driving force during flow (drag, lift or collision). Nonlinearity of these multiphase interactions yield a variety of flow phenomena which are modelled using two major approaches. These include; the Lagrangian tracking of computational particles coupled with the Eulerian flow description of the continuous phase and the Eulerian-Eulerian description in which the solid particles are represented as a random field in the Eulerian reference frame [5]. Accuracy of mathematical representation, consistency of accompanying closure models and numerical stability are the attributes that make these techniques very applicable. However, there are still opportunities for improvement in these models as far as the particle-particle interactions and limits on solid phase concentrations are concerned. The limitation of the Lagrangian-Eulerian approach in handling flow systems involving high solids concentration [2] (>12%) makes the Eulerian-Eulerian approach more suitable for this computational analysis.

The present study employs the tool of Computational Fluid Dynamics to simulate a two-phase Solid-Liquid (SL) flow in an annulus, by elucidating multiple state variable distributions (namely cuttings concentration, pressure drop profiles, axial fluid and solid velocities) as a function of several drilling parameters: hole eccentricity, inclination, ROP, drill-pipe rotation and fluid rheology. Anon-Newtonian (power law) fluid model with well described flow parameters [8] has been implemented, considering a uniform cuttings size distribution (3 mm). A commercial CFD software suite (ANSYS FLUENT 17.1) has been used: the descriptive and predictive potential of the CFD software has been confirmed on account of the reasonable agreement with previously published experimental data (a relative error of less than 7% is achieved), as illustrated by the corresponding sensitivity plots. This multi-parametric CFD analysis study of multiphase cutting transport during drilling applications has confirmed that fluid velocity, hole inclination and annular eccentricity are the most influential factors governing the cuttings transport efficiency.

LITERATURE REFERENCES

1. Chin, W. C. (2001). Computational Rheology for Pipeline and Annular Flow: Non-Newtonian flow Modeling for Drilling and Production, and Flow Assurance Methods in Subsea Pipeline Design, Gulf Professional Publishing.
2. Pereira, F. A. R., Ataide, C. H., & Barrozo, M. A. S. (2010). A CFD Approach using a discrete phase model for annular flow analysis. Latin American applied research, 40(1), 53-60.
3. Abdulkadir, M. (2011). Experimental and Computational Fluid Dynamics (CFD) studies of gas-liquid flow in bends, PhD Thesis, University of Nottingham, UK.
4. Gerogiorgis, D. (2013). Isothermal CFD modeling of annular multiphase flows during Underbalanced Drilling (UBD) in oil reservoirs, paper presented at the 2013 AIChE Annual Meeting, San Francisco, CA, USA.
5. Subramaniam, S. (2013). Lagrangian–Eulerian methods for multiphase flows. Progress in Energy and Combustion Science, 39(2), 215-245.
6. Li, Y., & Kuru, E. (2003). Numerical modelling of cuttings transport with foam in horizontal wells. Journal of Canadian Petroleum Technology, 42(10) (PETSOC 03-10-06).
7. Ofei, T. N., Irawan, S., & Pao, W. (2014). CFD method for predicting annular pressure losses and cuttings concentration in eccentric horizontal wells. Journal of Petroleum Engineering, 486423, 1-16.
8. Rooki, R., Ardejani, F. D., Moradzadeh, A., & Norouzi, M. (2014). Simulation of cuttings transport with foam in deviated wellbores using computational fluid dynamics. Journal of Petroleum Exploration and Production Technology, 4(3), 263-273.