Essay Example on Cutting Transport: Issues and Solutions
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Cuttings transport in the process of drilling, which is done either with coiled tubes or conventionally has a major influence on the drilling economics. For instance, ineffective cleaning of the holes from the drilled cuttings often leads to many problems, including the reduction of weight on bits that leads to minimizing the penetration rates, stuck pipes, extra pipe wear, blockages of the transient holesthat leads to improper circulation situations, wasted time for wiper tripping, and additional costs introduced due to additives presemt in the fluid used for drilling.
The challenges have provoked research into the cuttings transport field in the past decades. Mostly, it has been found out that the velocities of the fluid should be increased to attain increased turbulent flow, as well as optimizing mud rheology to enhance the turbulence in horizontal or inclined well bore sections [2]. Other factors that need consideration and investigation include turbulence in the flow of various non-Newtonian liquids, and thus, there is need to consider cuttings transport properties, including dynamics of conventional drilling and pipe rotation [2].
The problems also point to the importance of adequate cuttings removal from the well during the process of rotary drilling, which is critical for cost-effective drilling. The build-up of high annular cuttings in most occasions leads to stuck drill pipe among other impediments to standard drilling and completion procedures. Importantly, many factors affect cuttings transport. However, the options that are available for efficient transport are few. Influential parameters, including mud density and hole angle, are usually predetermined for various reasons, such as fluid and rock in-situ characteristics and a well-planning strategy [1]. Other variables that are worth consideration include drill-cutting physical properties, which are mostly uncontrollable. Therefore, to ensure adequate hole cleaning drilling the drilling process, mud rheology and flow rate have to be accounted for.
Identification of Cutting Transport Issues and their Solutions
The inclination angle of hole sections plays a significant role into the effectiveness of cutting transport. For instance, the inclination angle for unweighted muds at annular velocities of 37m/min, the cutting volume at an angle of 300 are in most instances the to four times greater compared to when the angle is vertically oriented [1]. Further, at angles of 450, the cuttings were characterized of hazardous behaviour because they form beds that can slip downward inside the hole sections during the process of drilling, as well as avalanching towards the bottom hole after the process of circulation halts. For the annular mud velocities of 46m/min, concentrations also influenced the effectiveness of flow, and concentrations that were favourable were 2-6 vol% for the cutting holes from vertical to 450 when the mud density exceeds 1438kg/m3.
The particle concentration and the mud velocity also affects the effectiveness of cutting transport. In essence, mud velocity plays a significant role in transporting the cuttings, the higher the velocity, the lesser the probability that the particles will slip downward or avalanche. Therefore, the probable solution is using a high velocity. Besides, the viscosity or the concentration of the particles is also vital aspect when considering cuttings transport. The lesser the concentration, the higher the effectiveness of transporting the cuttings through drilling. However, the concentration of the particles also affects the viscosity at different mud velocities as shown in the Figure 1 below [1].
Figure 1: Effect of fluid viscosity on annular cuttings concentration. [1]
From Figure 1 above, as the mud velocity increases, and the fluids apparent and effective viscosity remain constant, and the cutting angle being held at 300, the concentration drops, making it easier to transport the cuttings. For this reason, to achieve effectiveness in transporting the cuttings, it is vital to increase the mud velocity, thereby eliminating the problem of particles slipping backwards.
In addition, critical conditions, including the critical velocity of bed erosion play a significant role in cuttings transport. The critical velocity is referred to as the average velocity of the cuttings fluid , at which the cuttings start moving, which is obtained by monitoring the stationary bed of the cuttings and subsequently analysed using videos at each flow rate for any possible movement of the cuttings [3]. Table 1 highlights the critical velocity at the instance when the cuttings state moving, which is reconstructed in Figure 2, where the performance of variant fluids are compared. As shown in Table 1 and Figure 2, water always initiates the movement of the cuttings at lower velocities compared to more vicious fluids.
Table 1- Critical velocities required for initiating the movement of cuttings
Figure 2: The critical velocities vs the fluid types used in the movement if cuttings based on the cutting size. [3].
As the polymer concentration and fluid viscosity increases, higher critical velocities are required to initiate the movement of the cuttings. Additionally, for the smallest cuttings used, which is 260 micron, fluids characterized of the highest polymer concentrations were not able to remove the cuttings within the flow rate limits of the pumps used, and thus, it was recommended that water was the best cleaning fluid for beds compared to HEC solutions [3]. Further, water is more favourable for eroding the cuttings bed while polymers are best in the prevention of bed formation.
References
[1]T. Becker, J. Azar, and S. Okrajni, "Correlations of Mud Rheological Properties With Cuttings-Transport Performance in Directional Drilling," SPE Drilling Engineering, vol. 6, no. 01, pp. 16-24, 1991.
[2]V. Kelessidis and G. Bandelis, "Flow Patterns and Minimum Suspension Velocity for Efficient Cuttings Transport in Horizontal and Deviated Wells in Coiled-Tubing Drilling," SPE Drilling & Completion, vol. 19, no. 04, pp. 213-227, 2004.
[3] M. Bizhani, F. E. Rodriguez-Corredor, and E. Kuru, Hole Cleaning Performance of Water vs. Polymer-Based Fluids Under Turbulent Flow Conditions, SPE Canada Heavy Oil Technical Conference, 2015.
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