Hole Cleaning During Underbalanced Drilling in Horizontal and Inclined Wellbore

Abstract

This paper is an extended work of SPE 90038. An aerated nonNewtonian flow and an inclined wellbore section were added to the previous model to study the hole-cleaning problem while drilling an underbalanced well. This new mechanistic model for cuttings transport was developed by combining two-phase hydraulic equations, turbulent boundary layer theory, and particle transport mechanism. It is shown that the model is useful for predicting minimum annular velocity and cuttings bed thickness in horizontal and inclined wellbore geometry. Effects of temperature, bottom hole pressure, liquid flow rate, gas injection rate, cuttings size and density, inclination angle, and rheological properties of drilling mud on hole cleaning are analyzed using this mechanistic model. The model is validated by available experimental data. Computer simulation indicates that cuttings bed thickness is very sensitive to the liquid phase flow rate. It dominates cuttings transport efficiency. However, during underbalanced drilling, increase of liquid phase fraction may not always be feasible while trying to keep a low equivalent circulating density (ECD). Meanwhile, injection of gas has positive effects on cuttings transportation depending on the flow patterns and drilling mud viscosity. Elevated temperature causes a significant increase of bed thickness, and it is important to recognize this negative effect, especially when drilling highpressure/high-temperature (HPHT) wells. The effect of pressure on cuttings concentration is negative. Larger size and heavier cuttings make hole cleaning more difficult and require higher pump rates for low-viscosity fluids. Increases of liquid phase density result in better hole cleaning. The range of hole angles from approximately 35 o to 60 o (from vertical) is the most difficult for cuttings transport. Frictional pressure losses in a deviated wellbore highly depend on cutting bed thickness. Simulation results are compared to available experiment data and show good agreement. In summary, this paper presents a model that is useful for practical hole cleaning during underbalanced drilling (UBD).

Experimental Investigation of Cuttings Transport in Horizontal Wells Using Aerated Drilling Fluids

“…Zhoue [22] made an experimental study in 73 ft. long 6 in -3. decreasing the pressure drops in cuttings transport cases.…”

Reservoir Characterization during Underbalanced Drilling of Horizontal Wells Based on Real-Time Data Monitoring

“…In this paper, we consider the effect of cutting bed by evaluating the open flow area of gas liquid two-phase fluid in horizontal annulus causing the movement of cutting bed. The cuttings transport in horizontal wellbore has been investigated by many researchers [24][25][26][27][28][29][30]. In this paper, we use a mechanics model with aerated drilling fluid proposed by Zhou [30] to predict the movement of cutting bed and the cutting bed height.…”

Experimental Study of Hole Cleaning Performance of Underbalanced Drilling at Downhole Conditions

“…However, cuttings properties, fluid density, inclination and eccentricity also have some effects on cuttings transport. Zhou [11] carried out experiments where effects of liquid and gas flow rates on cuttings transport were investigated under elevated pressure and elevated temperature (EPET). The results showed that liquid flow rate, gas-liquid ratio and temperature essentially affect cutting transport efficiency and frictional pressure drop.…”