Reza Ettehadi Osgouei

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

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.

A New Model to Determine the Two-phase Drilling Fluid Behavior Through Horizontal Eccentric Annular Geometry, Part A: Flow Pattern Identification and Liquid Hold-up Estimation

Flow patterns, liquid holdup, and frictional pressure gradient are three importance parameters to study the multiphase drilling fluid behavior. Although two-phase fluid flow is studied in detail for pipes, there exists a lack of information about aerated fluid flow behavior inside a wellbore. This study aims to identify the flow patterns of gasified fluids flowing inside a horizontal annulus, and to develop a method for measurement of liquid holdup by using the image processing techniques. 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 high-speed camera is used for recording each test dynamically for the identification of flow patterns and the measurement of liquid holdup.

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.

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