Mehmet Evren Ozbayoglu

Critical Fluid Velocities for Removing Cuttings Bed Inside Horizontal and Deviated Wells

Abstract This study aims to estimate the critical fluid flow velocity for preventing the development of a stationary bed using empirical correlations valid for horizontal and highly inclined wellbores that can be easily used at the field. For this purpose, experiments have been conducted at METU-PETE Cuttings Transport Flow Loop for various conditions. Observations showed that a stationary bed is developed when the fuid velocity is less than 6.0 ft/s, and a critical fluid velocity of 8.0 ft/s is required to establish a no-bed condition. Results showed that the critical velocity and the thickness of the stationary bed, if developed, could be estimated with a reasonable accuracy.

CFD Simulation of Solids Carrying Capacity of a Newtonian Fluid Through Horizontal Eccentric Annulus

It is essential to transport cuttings generated in drilling operations to the surface for disposal. As the inclination of wellbore increases, cuttings begin to deposit in the lower section of the wellbore, and develop cuttings bed. This developed bed increases the mechanical friction between the drillstring and the wellbore. As a result, problems such as increase in torque, decrease in force transfer to the bit, and poor control of the bottom hole pressure arise. Estimation of total concentration of cuttings inside the wellbore has never been an easy task. Cuttings and fluid dragging them to be transported have different relative velocities inside the wellbore, causing variations in pressure drop. Hence, a better understanding in cuttings–liquid interactions inside the wellbore is required.In this study, the interactions between cuttings and drilling fluid in horizontal eccentric annulus were simulated and observed using commercial Computational Fluid. CFD software program has proven to be a successful tool in studying complex fluid mechanic problems that are difficult to solve analytically. The effect of fluid flow rate and the impact of the rate of penetration (ROP) on flow patterns, cuttings concentration and pressure losses were investigated and validated using data obtained from Middle East Technical University Petroleum and Natural Gas Engineering Department Cuttings Transport / Multiphase Flow Loop. The drilling fluid of study is limited to water, a Newtonian fluid. The results obtained from the simulations show good agreement with the experiments. As the drilling fluid flow rate increases, the flow pattern was observed changing from stationary bed to dispersed flow, which complies with experimental results and literature findings. Increase in flow rate overcomes the gravitational force that pulls the cuttings downward and increases the surface forces that lift the cuttings up to the surface. Consequently, by increasing annular flow rate, cuttings concentration is decreased. On the other hand, the increment in ROP leads to more cuttings generated and more cuttings accumulation in the well bore. In conclusion, fluid flow rate and ROP are both significant factors in hole cleaning operations. The higher the flow rate, the higher the efficiency of hole cleaning, whereas the higher the ROP, the less efficient is the hole cleaning. CFD is proven to be successfully applied to predict the solid concentration in the well. Therefore this tool can be used for more complex cases, and the information provides can be very useful especially when there is no any other data available.Copyright

Laboratory Investigation on Gelation Behavior of Xanthan Crosslinked with Borate Intended To Combat Lost Circulation

............................................................................................................iv ÖZ .............................................................................................................................v ACKNOWLEDGEMENTS.......................................................................................ix TABLE OF CONTENTS ...........................................................................................x LIST OF TABLES ...................................................................................................xii LIST OF FIGURES.................................................................................................xiii NOMENCLATURE.................................................................................................xv CHAPTERS 1.INTRODUCTION...................................................................................................1 2.LITERATURE REVIEW........................................................................................3 3.STATEMENT OF THE PROBLEM .....................................................................11 4.THEORY..............................................................................................................13 4.1. Chemistry of crosslinking ...........................................................................13 4.2. Rheological models ....................................................................................15 5.EXPERIMENTAL WORK ...................................................................................19 5.1. Materials ....................................................................................................19 5.2. Experimental method..................................................................................21 5.3. Experimental procedure..............................................................................22 6.RESULTS AND DISCUSSIONS..........................................................................28 6.1 Effect of pH-controller on gelation ..............................................................28 6.2. Effect of poly-cross concentration on gelation ............................................31 6.3. Effect of magnesium chloride on gelation ...................................................34 6.4. Effect of temperature on gelation................................................................36 6.5. Effect of mixing time on gelation................................................................39 6.6. Effect of Shear history on gelation..............................................................41

An Experimental and Numerical Study of Two-phase Flow in Horizontal Eccentric Annuli

The aerated fluids have a potential to increase rate of penetration, minimize formation damage, minimize lost circulation, reduce drill pipe sticking, and, therefore, assist in improving the productivity. The technology of drilling using aerated fluids in the area of offshore drilling is very common. The use of compressible drilling fluids in offshore technology has found applications in old depleted reservoirs and in the new fields with special drilling problems. However, the drilling performed with gas-liquid mixture, calculating the pressure losses and the performance of cutting transportation is more difficult than single-phase fluid due to the characteristics of multi-phase fluid flow. In case configured drilling is directional or horizontal, these types of calculations are becoming more difficult depending on the slope of the wells. Both hydraulic behavior and mechanism of cutting transportation of the drilling fluids formed by gas-liquid mixture are not fully understood yet, especially there is a large uncertainty in selection of most appropriate flow regarding two phases. In this study, gas-liquid flow inside horizontal eccentric annulus is simulated using an Eulerian-Eulerian computational fluid dynamics model for two-phase flow patterns in an annulus, i.e., dispersed bubble, dispersed annular, plug, slug, wavy annular. A flow loop was constructed in order to conduct experiments using air-water mixtures for various in-situ air and water flow velocities. A digital high speed camera is used for recording each test dynamically for identification of the liquid holdup and flow patterns.

PHPA as a Frictional Pressure Loss Reducer and Its Pressure Loss Estimation

Abstract This article analyzes the performance of a liquid polymer emulsion containing partially hydrolyzed polyacrylamide/polyacrylate (PHPA) copolymer as a circulating system pressure loss (drag) reducer. Straight cylindrical pipe flow experiments were performed at different concentrations of solutions for measuring frictional pressure losses. Comparison of measured and theoretical frictional pressure loss values showed that as the PHPA concentration increased, considerable drag reduction (as high as 60%) was achieved and the optimum PHPA concentration for drag reduction purposes was estimated as 0.0020 (v/v). A friction factor is developed as a function of PHPA concentration and Reynolds number, and the results show that the pressure losses can be estimated with an error less than 15% by using the proposed friction factor.

Friction Factor Determination for Horizontal Two-Phase Flow Through Fully Eccentric Annuli

Abstract In this study, empirical friction factor correlations were developed for two-phase stratified- and intermittent-flow patterns through horizontal fully eccentric annuli. Two-phase flow hydraulics were investigated, and a flow pattern prediction model is proposed. The friction factor correlations were validated using experimental data collected at the multiphase flow loop METU-PETE-CTMFL. Two different geometrical configurations were used during experiments—that is, 0.1143 m inner diameter (ID) casing, 0.0571 m outer diameter (OD) drillpipe; and 0.0932 m ID casing, 0.0488 m OD drillpipe. The eccentric annuli has been represented by representative diameter d r . A new mixture Reynolds number based on liquid holdup is proposed for friction factor determination.

Comparative Study of Yield-Power Law Drilling Fluids Flowing Through Annulus

Abstract An exact solution for calculating the frictional pressure losses of yield-power law (YPL) fluids flowing through concentric annulus is proposed. A solution methodology is presented for determining the friction factor for laminar and nonlaminar flow regimes. The performance of the proposed model is compared to widely used models as well as the experimental results of 10 different mud samples obtained from the literature. The results showed that the proposed model could estimate the frictional pressure losses with an error of less than 10% in most cases for both laminar and nonlaminar flow regimes, more accurately than the widely used models available in the literature.

Modelling of Two-Phase Flow Through Concentric Annuli

Abstract A mathematical model is introduced in order to predict the flow characteristics of multiphase flow through an annulus. Flow patterns and frictional pressure losses estimated using the proposed model are compared with the experimental data of a wide range of liquid and gas flow rates recorded at a flow loop consisting of numerous circular pipes and annulus. The results showed that the model predictions for flow patterns and frictional pressure losses are reasonably accurate. Moreover, it is observed that geometry and liquid phase viscosity have a significant influence on flow pattern transitions and frictional pressure losses.

The Determination of Two Phase Liquid-Gas Flow Behavior Through Horizontal Eccentric Annular Geometry by Modification of Beggs & Brill and Lockhart & Martinelli Models

Gas-liquid flow in annular geometries is the one of the most frequently encountered flow conditions in petroleum industry, either during drilling operations if aerated fluids are used, or production stages, if the produced fluid is under bubble point pressure. With the increase in the interest in horizontal / extended reach wells, understanding the flow behavior of gas-liquid mixtures in horizontal wells is essential for better pressure control downhole. Although two-phase fluid flow is studied intensively for circular pipes, there exists a lack of information about aerated fluid flow behavior inside annular geometries, both theoretically and experimentally. Existing two-phase fluid flow models available in the literature developed for circular pipes are performing poorly for annular geometries. Using hydraulic diameter definitions or effective diameter terms simply give inaccurate results for both flow pattern estimations and friction pressure loss determination. This study aims to identify the flow patterns of gasified fluids, and to determine frictional pressure losses for two phase flow through horizontal eccentric annular geometry. In order to develop the liquid holdup, Digital Image Processing Techniques have been used. Friction pressure losses are determined by applying two different methods; i) Modifying Lockhart-Martinelli parameter, and ii) Modifying Beggs and Brill’s method, originally developed for circular pipes. Experiments have been conducted at Middle East Technical University (METU) Multiphase Flow Loop using air-water mixtures with various in-situ flow velocities. A digital camera is used for recording each test dynamically for the identification of flow patterns and the measurement of liquid holdup. Friction pressure losses are recorded during each test. The comparison of modified models with experimental data indicates that liquid holdup and friction pressure losses can be estimated with a reasonable accuracy. The information obtained from this study is critical, since very limited information is available in the literature for modeling two-phase flow behavior.Copyright

A Mechanistic Model for Predicting Frictional Pressure Losses for Newtonian Fluids in Concentric Annulus

Abstract A mathematical model is introduced estimating the frictional pressure losses of Newtonian fluids flowing through a concentric annulus. A computer code is developed for the proposed model. Also, extensive experiments with water have been conducted at Middle East Technical University, Petroleum and Natural Gas Engineering Department Flow Loop and recorded pressure drop within the test section for various flow rates. The performance of the proposed model is compared with computational fluid dynamics (CFD) software simulated annulus flow section and various criteria such as crittendon, hydraulic diameter and slot flow approximation as well as experimental data. The results showed that the proposed model and experimental results are in good agreement for almost all cases when compared with the other criteria and CFD software. Also, the proposed model could estimate the frictional pressure losses for both laminar and turbulent flow regimes within an error range of ±10%.