Directional Drilling Hydraulics Optimization Using Conventional and Nano Based Drilling Fluids

Directional Drilling Hydraulics Optimization Using Conventional and Nano Based Drilling Fluids

Chapter One

Study Objectives and Significance of Study

What are the impacts of the turbulence criteria and effective annular diameter definitions on drilling hydraulics and efficient hole cleaning in directional wells? What are the conclusions from the combined effects of these factors and fluid rheology on directional wells? Can nano- fluids improve rig hydraulics and hole cleaning? In order to answer these questions, the following objectives are proposed.

1. To examine the impact of different equivalent annular diameter definitions on the pressure drop and hole cleaning in directional
2. To examine the possible influence of nano-fluids on drilling hydraulics and hole
3. To investigate the impact of fluid rheology on pressure drop and hole cleaning in directional wells.
4. To develop a user-friendly software to facilitate quick evaluation of the optimization process

CHAPTER TWO

THEORETICAL BACKGROUND

Rotary Rig Hydraulics

Rotary drilling is the act of using torque-powered bits to make holes. The drilling rig consists of six (6) primary sub-systems: the power system; the hoisting system; the rotary system; the circulating system; well control system; and well monitoring system. The circulating system transmits the drilling fluid from the surface through the system and back up the annulus to the surface. Hydraulics optimization is implemented and achievable through careful planning, design, selection, installation, and operation of all the rig components especially the circulating system. Hydraulics is greatly affected by drilling fluid rheology.

Rheology of drilling fluids

Several rheological models are available in the literature to describe the deformation and flow of drilling fluids. These include:

1. NewtonianModel
2. Bingham PlasticModel
3. Power Law Model (Ostwald de Waele’smodel)
4. Yield Power Law Model (Herchel Bulkleymodel)
5. API RP 13DModel
6. Other

The simplest rheological model is the Newtonian model, which is simply a linear relationship between the shear stress and the shear strain. The Newtonian model has well established fluid flow and pressure loss equations due to its simplicity. Therefore, the related equations developed for Newtonian fluids are the basis for all the other models, except for those that were determined empirically. The definition of an apparent or effective viscosity comparable with the true viscosity of the Newtonian model facilitates the derivations. This apparent viscosity serves as the basis for determining the Reynold’s number and defining the fluid flow regime.

Newtonian Model

The Newtonian model is a simple linear relationship between shear stress and shear strain rate.

The governing equation is

t = mgɺ

where,

t = shear stress(lbf

/100 ft ² ),

m = viscosity, poise (centipoise(cp))

gɺ = shear strain rate (sec^–1 )

Bingham Plastic Model

For decades, the petroleum industry used the Bingham Plastic Model to describe the rheology of drilling fluids. The model incorporates a yield stress necessary to initiate flow

The governing equation is:

t =t0 + m_pgɺ

2.2

where,

t = shear stress (lbf   /100 ft² )

t0  = yield  point, (lbf

/100 ft² )

m_p = plastic viscosity, cp(centipoise)

gɺ = shear strain rate(sec^–1)

Power Law Model (Ostwald de Waele’smodel)

Ostwald de Waele’s Power law model presented a new approach to the study of deformation and flow of drilling fluids. He defined a consistency factor and a flow behaviour index.

The governing equation is:

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CHAPTER THREE

METHODOLOGY AND COMPUTER PROGRAM

Hydraulics

The following assumptions are used to develop the relevant equations (Bourgoyne et al. 1991):

1. The drillstring is placed concentrically in the wellbore
2. There is no rotation of the
3. The sections of the open hole are circular in shape and of known diameter
4. Drilling fluid is incompressible
5. Flow is isothermal
6. Pipe is

As stated in chapter 1, the main factors of a hydraulics program are the fluid properties (rheology and density), well bore geometry (inclination, hole or casing diameter, drill pipe and drill collar diameters and lengths), and formation characteristics (pore pressure, fracture gradient, and maximum allowable ECD). The subsequent sections present the various rheological models equation as well as pressure drop equations used in this work.

Pressure, and Velocity Calculations Along The WellBore

In rotary drilling operations, the circulating system transmits the drilling fluid from the surface through the well bore and back to the surface. The mud pumps provide the energy that transmits the drilling fluid from the mud pit through the suction line to the standpipe, down the drillstring, out through the drill bits, up through the annulus, to the mud treatment devices through the return line, and back to the mud pit. The mud treatment equipment includes the shaleshaker, desander, desilter, and degasser which are used to remove solids, gases and other impurities from the drilling fluid. Thus, from the principle of conservation of energy, the sum of the pressures along the well geometry (assuming no influx or efflux of formation fluid) must be equal to the pump pressure. From the perspective of bit hydraulics optimization, all other pressures are said to be parasitic.

CHAPTER FOUR

DATA ANALYSIS, RESULTS, DISCUSSIONS, AND SENSITIVITY ANALYSIS

This chapter is divided into 2 sections:

1. To perform sensitivity analysis of the effect of inclination, rheological models, and equivalent annular diameter definitions on annular pressure and equivalent circulating density
2. To examine the impact of nanoparticles on annular pressure and equivalent circulating density (ECD). The influence of nanofluids is examined by the addition of aluminium oxide nanoparticles to a base

For these analyses, a 5 in OD drill pipe, 12.25 in hole, and 150 gal/min flow rate are used. The rheological models and equivalent annular diameter equations are applied to the same problem to have a single basis for comparison.

CHAPTER FIVE

SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

 Summary

Hydraulics optimization is an attempt to maximize the pressure drop across the bit in order to ensure adequate rate of penetration, and effective hole cleaning. The hydraulics system is centered around well geometry and fluid properties, and thus drilling fluids and hydraulics have common purposes. The total pressure loss along the wellbore is the sum of the pressure drops in the drillstring and in the drillstring annulus. The pressure drops are functions of the flow regime, which depends on the Reynold’s number. This study proposed to provide a means for quick evaluation of the well plan, examine the impact of available fluid rheological models and equivalent annular diameter definitions on hydraulics optimization, and to examine the possible impact of nanofluids on hydraulics optimization using different effective viscosity correlations.

Conclusions

The following conclusions were drawn from the analysis:

1. The Hydraulic Radius concept, Slot Approximation, and Lamb’s Approach give almost the same pressure gradients for various rheological
2. The Crittendon correlation overestimates the values of the annular pressure gradient and ECD for various rheological models. This phenomenon is compounded when the fluid is not in the laminar flow
3. The pressure gradient decreases with increasing inclination from the vertical for all rheology and equivalent annular diameter
4. The increase in density and viscosity of the nanofluid compared to the base fluid leads to the need for a higher capacity pump to flow the system. However, using a low density and low viscosity base fluid, with lower density and concentration of nanoparticles would reduce the effect of increase in the density and viscosity of the
5. A user-friendly computer program in MATLAB was developed to facilitate the computation of the pressure gradients. This definitely eliminates error in hand calculations

Recommendations

The API and IADC give detailed guidelines of procedures for hole cleaning and other drilling and completions operations. The computer program is a means of quick evaluation. The use thereof, does not eliminate the need for sound engineering practices and principles, to ensure safe, economic, and environmentally responsible delivery of the well. Consequently, the following recommendations for further studies are made.

1. This work ignores the effect of nanoparticles on fluid rheology. Future studies should incorporate the rheology of
2. The computer program should be developed further in order to improve its robustness. It uses the Rubiandini’s cuttings transport model. The API, however, recommends the use of a cuttings chart.

REFERENCES

• API RP 13D,: “Rheology and Hydraulics of Oil-well Fluids,” May 2010.
• Bahari, A., and Baradan Seyed, A.,: “Drilling Cost Optimization in Iranian Khangiran Gas Field,” SPE 108246, 1967.
• Bailey, W.J. and Peden, J.M.,: “A Generalized and Consistent Pressure Drop and Flow Regime Transition Model for Drilling Hydraulics,” SPE Drilling and Completions, Vol 15, No. 1, March 2000.
• Bern, P.A., Morton, E. K., Zamora, M., May, R., Moran, D., Hemphill, T., Robinson, L., Cooper, I., Shah, S., and Flores, D.V.,: “Modernization of the API Recommended Practice on Rheology and Hydraulics : Creating Easy Access to Integrated Wellbore Fluids Engineering,” IADC / SPE 98743, 2006.
• Bourgoyne Jr., Adam. T . Millheim, Keith . K., Chenevert, Martin. E, Young Jr., F.S.,: “Applied Drilling Engineering,” 1991
• Cho, H., Subash, N.Shah., and Osisanya, S.O.,: “A Three-Segment Hydraulic Model for Cuttings Transport in Horizontal and Deviated,” SPE / Petroleum Society of CIM 65488, 2000.
• Cho, H., Subash, N.Shah., and Osisanya, S.O.,: “A Three-Layer Modeling for Cuttings Transport with Coiled Tubing Horizontal Drilling,” SPE 63269, 2000.
• Cho, H., Subash, N.Shah., and Osisanya, S.O.,: “Effects of Fluid Flow in a Porous Cuttings-Bed on Cuttings Transport Efficiency and Hydraulics,” SPE 71374, 2000.
• De Sa’, C.H.M., Martins, A.L. and Amaral, M.S., Petrobras S.A., “A Computer Programme for Drilling Hydraulics Optimization Considering Realistic Rheological Models,” SPE 27554, 1994.
• Ford, J.T., Gao, E., Oyeneyin, M.B., Peden, J.M., Larrucia, M.B., and Parker, D.,: “A New MTV Computer Package for Hole Cleaning Design and Analysis,” SPE Drilling and Completions, September 1996.
• Garcia-Hernandez, A., Miska, S.Z., Yu, M., Takach, N.E., and Zettner, C.,:”SPE 109630 Determination of Cuttings Lag in Horizontal and Deviated Wells,” SPE 109630, 2007.

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