Optimization of Hole Cleaning and Cutting Removal in Vertical, Deviated and Horizontal Wells
- Mehdi Mohammadsalehi (National Iranian Oil Co.) | Nozar Malekzadeh (Curtin University)
- Document ID
- Society of Petroleum Engineers
- SPE Asia Pacific Oil and Gas Conference and Exhibition, 20-22 September, Jakarta, Indonesia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.6.6 Directional Drilling, 1.6 Drilling Operations, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.10 Drilling Equipment, 1.11.5 Drilling Hydraulics, 1.7.7 Cuttings Transport, 1.11 Drilling Fluids and Materials
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As measured depths and displacements in horizontal and extended-reach (ERD) wells increase, good hole cleaning and cuttings removal is essential to avoid associated problems with poor hole cleaning like pipe sticking, abnormal torque and drag, drop in ROP and etc. So far, some methods and models have been developed that can assist in finding the minimum flow rate required to efficient removal of the cuttings during drilling operation. One of them is Larsen's model that predicts minimum flow rate for cuttings removal from 55 to 90 degrees of inclination. Another model, Moore's correlation, is used to find the slip velocity of the cuttings in vertical wells (0 degree inclination). This paper presents a detailed combination of Larsen's model and Moore's correlation to predict and calculate the minimum flow rate for cuttings removal for all range of inclinations namely from 0° to 90°. The resultant flow rate is compared with flow rate that maximizes the bit horsepower or bit jet impact force (optimized flow rate). If the flow rate for cuttings removal is less than the optimized flow rate, the latter is selected. But if the flow rate for cuttings removal is higher than the optimized flow rate, then drilling fluid rheological properties should be changed until the optimized flow rate becomes higher than the flow rate for cuttings removal. This procedure gurantees achievement both optimized drilling hydraulics and good hole cleaning. To illustrate the usability of this approach whitin all inclination ranges, three points in vertical, deviated and horizontal parts of a horizontal well are chosen and the optimization procedure performed and presented.
It has been recognized for many years that removal of the cuttings from the wellbore during drilling poses special problems. Until the early 1980's vertical drilling operations outnumbered deviated and horizontal drilling operations. Thus most effort was put into understanding the hole cleaning in vertical wells. Poor hole cleaning may result in lost circulation, hinder the casing or liner running jobs, excessive overpull on trips, high rotary torque, excessive equivalent circulation density, formation break down, slow ROP, excessive bit wearing and pipe sticking problems[1,5]. The major factors that influence cutting transport are namely; drill pipe eccentricity, wellbore size and inclination, drilling fluid density, cuttings size, cuttings density, drill pipe rotation, drilling rate, drilling fluid rheology and flow rate. Practical use of these parameters to control cuttings transport is however very much depending on their controllability in the field. For example drill pipe eccentricity has a strong influence on the cuttings transport. However it is very difficult to control and/or assess the degree of eccentricity during the drilling operation. Figure 1 illustrates these factors in relation to their ease of control in the field.
Drilling fluid rheology and flow rate are the two main parameters which would influence cuttings transport strongly while their control in the field is relatively easy . Based on these facts several methods and models have been introduced that can be used to find the minimum flow rate required to remove the cuttings from the well for a specific drilling condition and drilling fluid rheological properties. Larsen's model can be used to find the minimum flow rate for cuttings removal from 55 to 90 degrees of inclination . Another one is Moore's model that is used to find the slip velocity of cuttings in vertical wells . In this study a computer programming in MATLAB® was developed that combines these two methods and predicts the minimum flow rate for cuttings transport from 0 to 90 degrees of inclination. Another computer program was written that calculates the optimum flow rate for different drilling fluid rheological properties using both hydraulic horsepower and jet impact force criteria. Then these two programs are combined to find that rheological properties of the drilling fluid that gives the optimized flow rate higher than the flow rate to remove the cuttings from a horizontal well called YS5, drilled in Yorte-E-Sha field inVaraminin Iran.
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