Evren Ozbayoglu

Estimating Flow Patterns and Frictional Pressure Losses of Two-Phase Fluids in Horizontal Wellbores Using Artificial Neural Networks

Abstract Underbalanced drilling achieved by gasified fluids is a very commonly used technique in many petroleum-engineering applications. This study estimates the flow patterns and frictional pressure losses of two-phase fluids flowing through horizontal annular geometries using artificial neural networks rather than using conventional mechanistic models. Experimental data is collected from experiments conducted at METU-PETE Flow Loop as well as data from literature in order to train the artificial neural networks. Flow is characterized using superficial Reynolds numbers for both liquid and gas phase for simplicity. The results showed that artificial neural networks could estimate flow patterns with an accuracy of ±5%, and frictional pressure losses with an error less than ±30%. It is also observed that proper selection of artificial neural networks is important for accurate estimations.

Frictional Pressure Loss Estimation of Non-Newtonian Fluids in Realistic Annulus With Pipe Rotation

The annular frictional performance of non-Newtonian fluids is among the major considerations during development of hydraulic programs for drilling operations. Proper estimation of the frictional pressure losses become more critical when determining hydraulic horsepower requirements and selecting proper mud pump systems to foresee any serious problems that might occur with hydraulics during drilling operations. Because the rheological behaviour of the non-Newtonian fluids is known to be challenging, it becomes even more complicated during pipe rotation, especially in eccentric wellbores. In many cases, significant differences are observed when theoretical calculations and measurements for pressure losses are compared. This study aims to develop correction factors for determining the frictional pressure losses accurately in eccentric horizontal annulus for non-Newtonian fluid, including the effect of pipe rotation. Extensive experimental work has been conducted on METU-PETE Flow Loop for numerous non-Newtonian drilling fluids, including KCl-polymer muds and PAC systems for different flow rates and pipe rotation speeds, and frictional pressure losses are recorded during each test. Rheological characteristics of the drilling fluids are determined using a rotational viscometer. Observations showed that pipe rotation has a significant influence on frictional pressure loss, especially at lower flow rates. Up to a point, as the pipe rotation increases, the frictional pressure losses also increase. As the flow rates are increased, the effect of pipe rotation on frictional pressure losses diminishes. Also, after a certain pipe rotation speed, no additional contribution of pipe rotation on frictional pressure loss is observed. When the developed friction factors are used, there is a good agreement between the calculated and observed frictional pressure losses for any pipe rotation speed.

Pressure Profile in Annulus: Solids Play a Significant Role

This paper looks into the effects of solids on the wellbore pressure profile under different conditions. An extensive number of experiments were conducted on a 90-ft-long, 4.5 in. 8 in. full-scale flow loop to simulate field conditions. The flow configurations are analyzed. A solid–liquid two-phase flow configuration map is proposed. Significant difference is found between the pressure profile with solids and without solids in the wellbore. The results of this study show how the pressure profile in the wellbore varies when solids present in the annulus, which may have important applications in drilling operations. [DOI: 10.1115/1.4030845]

Modeling Transient Circulating Mud Temperature in the Event of Lost Circulation and its Application in Locating Loss Zones

Lost circulation is one of the most persistent and costly drilling problems that drilling engineers have been struggling with for decades. The main reason why some of the remedial procedures are not working as planned is the lack of information, such as the location of the loss zone. The pinpointing of the zone of loss will allow the treatment to be applied directly to the point of loss rather than to the entire open hole.This paper presents an approach to predict the location of loss zone from the transient mud circulation temperature profile altered by the mud loss. A numerical model in estimating the transient mud circulating temperature profile during a lost circulation event is developed. The temperature profile in both the flow conduits (drillpipe and annulus) are modeled using mass and energy balance. The flow rate of drilling mud decreases in the annulus above the loss zone as part of the fluids lost into the fractures, which in turn alters the heat transfer between the drillpipe, annulus, and formation. The wellbore is divided into two multiple sections, which account for single multiple loss circulation zones. Rigorous heat transfer in the formation is included. Case studies are performed and numerical solution results are presented and analyzed. According to the results, temperature alterations induced by mud loss include: 1) Declines in both bottom-hole temperature (BHT) and mud return temperature over time, and 2) Discontinuity in the first order derivative of annulus temperature with respect to depth at the location of loss zone; meanwhile, the temperature alterations are mainly controlled by the mud loss rate and location of loss. By matching the simulated results with the distributed temperature measurements at different times, the depth of the loss zone can be identified. This piece of information is important for the spotting of LCM (lost circulation material) pills, the optimization of overbalance squeezing pressure, as well as the consideration of setting the cement plug or additional casing.Copyright

Sensitivity Analysis of Major Drilling Parameters on Cuttings Transport during Drilling Highly-inclined Wells

Abstract In this study, a layered cuttings transport model is developed for high-angle and horizontal wells, which can be used for incompressible non-Newtonian fluids as well as compressible non-Newtonian fluids (i.e., foams). The effects of major drilling parameters, such as flow rate, rate of penetration, fluid density, viscosity, gas ratio, cuttings size, cuttings density, wellbore inclination and eccentricity of the drillsting on cuttings transport efficiency are analyzed. The major findings from this study are, the dominating parameter on wellbore cleaning is the flow rate, and, as the viscosity of the fluid is increased, the thickness of the cuttings bed developed in the wellbore is significantly increasing. Also, cuttings properties, fluid density, wellbore inclination and eccentricity have some influence on cuttings transport.

Calculations of Equivalent Circulating Density in Underbalanced Drilling Operations

Underbalanced drilling using gasified fluids is one of the most widely used methods to drill depleted, low pressure and highly fractured formations. For ensuring a safe and successful underbalanced drilling operation, accurate prediction of the equivalent circulating density (ECD) is very important. Nevertheless, estimating ECD of gasified fluids is not easy due to the complexity of the two-phase fluid flow inside the wellbore. In this study, there are two major focuses considered; i) validation of the accuracy of Beggs & Brill (1973) model on the prediction of pressure losses of gasified fluids in underbalanced drilling operation, and modification of Beggs & Brill (1973) model for pressure loss estimation inside the wellbore, and ii) to propose an ECD calculation procedure for gasified fluids by using modified Beggs & Brill (1973) model. To validate the accuracy of Beggs & Brill (1973) model, experiments were carried out using Middle East Technical University (METU) Cuttings Transport Facility to obtain the pressure losses of gasified fluids in an annulus and their corresponding flow patterns. Air-water mixtures were used with various in-situ air and water flow velocities of 0-120 ft/s and 0-10 ft/s, respectively, at wellbore inclinations of 90°, 75°, 60°, 45° and 12.5° without inner pipe rotation. Pressures were recorded at several points along the annular test section, and pressure distribution along the test section was measured. Meanwhile, flow patterns were determined by the help of a high speed digital camera. Results showed that although Beggs & Brill (1973) model can estimate pressure losses in low gas and liquid flow rates and low slip ratio between two phases for horizontal and near horizontal annular sections with a reasonable accuracy, this model cannot accurately calculate pressure losses at inclined and vertical annular sections. With some modifications, improved Beggs & Brill (1973) model (by applying suggested procedure) can be used to predict ECD and annular pressure losses of gasified fluids inside the annulus accurately. This information can be directly applied for underbalanced drilling operations when gasified fluids are used.

Mathematical Modeling of Turbulent Flows of Newtonian Fluids in a Concentric Annulus with Pipe Rotation

Abstract In this study, a mathematical model is proposed to predict flow characteristics of Newtonian fluids inside a concentric horizontal annulus. A numerical solution, including pipe rotation, is developed for calculating frictional head losses in concentric annuli for turbulent flow. Navier-Stokes equations are numerically solved using the finite differences technique to obtain the velocity field. Experiments with water are performed in a concentric annulus with and without pipe rotation. Average fluid velocities are varied in the range of 1.1–3.3 m/s at various inner pipe rotations (0–120 rpm) in a horizontal concentric annulus. To verify the proposed model, estimated frictional pressure losses are compared with experimental data and the commercial software package ANSYS Workbench 10.0. The numerical model predicts frictional head losses with an error less than ±10% in most of the test cases.

Optimization of Liquid and Gas Flow Rates for Aerated Drilling Fluids Considering Hole Cleaning for Vertical and Low Inclination Wells

Underbalanced drilling (UBD) is one of the most widely used technologies preferred in depleted and/or low-pressured formations. In order to achieve underbalanced conditions, drilling fluids are usually gasified. Major drilling fluids preferred during UBD are pure gas, gas-liquid mixtures, and foams. This study is focused on gas-liquid mixtures. As the gas is introduced, the behaviour of the drilling fluid becomes hard to explain for many reasons. First of all, gas is compressible and physical properties of gas are very sensitive to changes in pressure and temperature. Second, a multiphase flow phenomenon arises. When there is multiphase flow, flow patterns should be considered. It is known that there is a difficulty to predict hydraulic behaviour of gas-liquid mixtures owing to this flow pattern dependence. During a drilling operation, one of the parameters that should be considered is hole cleaning. Hole cleaning is a challenging task even for a single-phase drilling fluid. Moreover, there is still a lack of information about how the cuttings are transported when gas-liquid mixtures are used as drilling fluids. Flow-rate optimization during UBD operations for liquid and gas phases are usually conducted based on formation pressures only. However, considering only this criterion as the optimization objective is misleading and may cause serious problems during the drilling operation. In this study, gas and liquid flow rates during UBD operations are conducted not only based on formation pressures, but also based on effective hole cleaning. It is assumed that liquid phase is the major contributor for cuttings transport, and gas phase is only influencing the bottomhole pressure. A mechanistic model is introduced for estimating the hydraulic behaviour of gas-liquid mixture drilling fluids under different flow patterns. Based on the bottomhole pressure and effective hole cleaning point of view, an algorithm is proposed for estimation of the optimum required flow rates for liquid and gas phases based on the introduced mechanistic model. Also, the model predicts the required backpressure that has to be applied.

Trajectory Estimation in Directional Drilling Using Bottom Hole Assembly Analysis

Abstract The aim of this study is to put together the basic concepts of mechanics on drill string which are related to directional drilling, thus finding a less complicated and more economical way for drilling directional wells. Slick bottom hole assembly, which has no stabilizers attached, and single stabilizer bottom hole assembly are analyzed through previously derived formulas gathered from the literature that are rearranged for this study. An actual directional well is re-drilled theoretically with a slick assembly and a computer program is assembled for calculating the side force and direction of the well for single stabilizer assembly. Influence of controllable variables on drilling tendency is investigated and reported. The study will be useful for well trajectory and drill string design in accordance with the drilling phase. Also, by using available data from the offset wells, the drilling engineer can back-calculate the formation anisotropy index that is often used for optimizing well trajectories and predicting drilling tendency on new wells in similar drilling conditions which is also shown throughout the study.

Development of a mixer-viscometer for studying rheological behavior of settling and non-settling slurries

Abstract Slurry transport has become a subject of interest in several industries, including oil and gas. The importance of slurry/solid transport in the oil and gas industry is evident in areas of cuttings transport, sand transport and, lately, hydrates. There is therefore a great need to develop instrumentation capable of characterizing fluids with high solid content. Presence of solids in fluids makes the rheological characterization of these systems difficult. This is because available rheometers are designed with a narrow gap and cannot prevent solids from settling. The main aim of this paper is to present a step-by-step procedure of converting torque and shaft speed into viscosity information by applying the Couette analogy, equivalent diameter and inverse line concepts. The use of traditional impeller geometries such as cone and plate may be challenging due to their narrow gap and inability to prevent settling. Therefore, the use of non-conventional impeller geometry is imperative when dealing with settling slurries and suspensions. The most challenging task using complex geometry impeller is data interpretation especially when dealing with complex rheology fluids. In this work, an autoclave is transformed into a mixer-type viscometer by modifying its mixing, cooling and data acquisition systems. Mathematical models relating the measured torque to shear stress and the measured shaft speed to shear rate were developed and expressed in terms of the equivalent diameter. The shear rate and shear stress constants were expressed in terms of equivalent diameter and measureable parameters such as impeller speed and torque. The mixer-type viscometer was calibrated using four Newtonian and four Power-Law fluids to determine the rheological constants (equivalent diameter, shear rate and shear stress constants). The concept of inverse line was used to identify the laminar flow regime. The calibrated instrument was used to characterize two Power-Law fluids. This procedure can be extended to any rheological model. Methods developed in this work can be used to characterize fluids with high solid content. This is particularly important when dealing with complex rheology slurries such as those encountered in food processing, oil and gas and pharmaceuticals.