TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractThe use of drilling foams is increasing because foams exhibit properties that are desirable in many drilling operations. A good knowledge of cuttings transport efficiency under downhole conditions is essential for safe and economical foam drilling. Previous cuttings transport studies with foam are limited to low pressure and ambient temperature conditions; no experimental study has been conducted under downhole (i.e. elevated pressure and temperature) conditions. This paper presents an experimental study of cuttings transport with foam in a horizontal annulus under simulated downhole conditions.Experiments were conducted to determine the effects of polymer additives, foam quality, flow velocity, temperature and pressure on foam cuttings transport. Experiments were carried out at elevated pressure (100 psi to 400 psi) and temperature (80°F to 170°F) conditions in a unique full-scale flow loop with a 73-ft long test section (5.76" × 3.5" concentric annulus). A field-tested commercial foam system consisting of surfactant (1% v/v) and Hydroxylethylcellulose polymer (HEC) was used in the experiments. Three different polymer concentrations (0.0%, 0.25% and 0.5% v/v) were tested. Foam quality was varied from 70% to 90%.During a test, cuttings were injected continuously to the flow loop until a steady state condition was established in the test section. In-situ cuttings volumetric concentration in the test section was determined using nuclear densitometers, load cell measurements, and by weighing cuttings flushed out of the flow loop. Test parameters recorded during the experiments were: liquid and gas injection rates, cuttings weight in injection and removal towers, mixture density, friction pressure loss, pressure and temperature in the annulus. * Now with Shell E & P Company, Houston, USA Two flow patterns, stationary cuttings bed and fully suspended flow, were observed during the cuttings transport tests. The flow pattern depends on polymer concentration, foam quality and annular velocity. Annular flow velocity, foam quality and polymer concentration all affect cuttings transport efficiency and frictional pressure loss. This paper will help to better design foam drilling and cleanup operations.
Extensive aerated mud experiments were performed in a unique field-scale elevated pressure and elevated temperature flow loop (6" × 3.5" annular test section, 73 ft length, horizontal configuration without drillpipe rotation). A view port was installed to observe flow patterns in the test section. Two nuclear densitometers were used to measure steady state mean void fraction. During test runs, the liquid and gas phase flow rates were in the range of 50–250 gal/min and 50–150 scf/min, respectively. For all the test runs, measurements of pressure drop and average liquid holdup over the entire annular section were carried out. The two-phase flow patterns were identified by visual observations through the view port. Stratified and slug flow were the two flow patterns observed over the range of the chosen test matrix. The presence of slug flow does not justify many existing simulation practices, which assume a homogeneous gas-liquid flow. A mechanistic model has been developed for aerated mud hydraulics based on conservation equations and existing two-phase pipe flow correlations. An extensive sensitivity analysis is presented to quantify the influence of mud properties and flow parameters on the bottom-hole pressure. Comparisons between the predictions of the model and experimental measurements show a satisfactory agreement. The present model is particularly suitable for the design of underbalanced coiled tubing applications. Introduction Coiled tubing has been shown to be a technically feasible method of drilling both oil and gas wells. One of the best applications of coiled tubing drilling technology is underbalanced drilling, to counteract the reduced weight on bit and annular velocities compared to conventional drilling. In some applications, aerated mud drilling has been recognized as having many advantages over conventional mud drilling, such as a higher penetration rate, less formation damage, reduced lost circulation, and lower drilling cost. Maintaining an optimum combination of liquid and air flow rates is important in aerated mud drilling operations. A useful prediction of the optimum combination requires knowledge of the flow pattern and determination of the properties of each phase under borehole conditions. Dukler and Hubbard1 developed a two-phase flow model based on phenomenological observations. Their study contributed a great deal of understanding about the mechanisms involved in hydrodynamic of slug flows. Based on their observations, Dukler and Hubbard defined an idealized slug unit and suggested a mechanistic model. It is the basis for a detailed mathematical model, which is capable for predicting hydrodynamic behaviors of slug flows, including the length, velocity, holdup and pressure distributions. A mathematical model for slug flows was developed by Ozawa and Sakaguchi2 based on the law of conservation of mass and momentum. This model predicts the position of a slug nose and tail, and pressure drop across the slug nose. The predictions showed a satisfactory agreement with experimental data. It was suggested that their approach could be used to study transient two-phase slug flows (solid-liquid or solid-gas flows). A Lagrangian approach was used by Gilchrist and Wong3 to study slug growth and acceleration effects associated with horizontal slug flows. The slug structure comprised of three sub-volumes: a liquid slug with entrained gas bubbles; a liquid film with a zero gas void fraction; and a gas bubble with zero liquid holdup. Mass and momentum equations were developed for the liquid slug and liquid film sub-volumes. An equation of state was used to formulate the changes in pressure in the gas bubble. A system of ordinary differential equations was coupled and solved simultaneously by a 4th order Runge-Kutta method. The simulated results for a particular slug unit showed fluctuations in the average slug velocity and void fraction in the liquid slug, and growth in the slug length as it traverses in a pipeline. Gomez and Shoham4 developed a mechanistic model for steady-state two-phase flows. The model is applicable for inclination angles from horizontal to vertical. The model predicts flow patterns, pressure drop, and liquid-holdup for stratified, slug, bubble, annular and dispersed bubbly flows.
Summary A discussion about horizontal foam-flow behavior in pipes and annular geometry under elevated pressures and temperatures is presented. The study is empirically based and covers the effects of foam quality, foam texture, pressure, temperature, and geometry of the conduit on the rheological response of foams. Introduction The use of lightweight fluids in drilling operations is becoming common practice worldwide. These fluids are normally used to induce underbalanced conditions (i.e., to keep the wellbore pressure below the formation's fluid pressure) while drilling in low-pressure reservoirs. This diminishes formation impairment from drilling fluid, enhancing productivity. It also is used to overcome operational difficulties such as stuck pipe and loss of fluid circulation. Other benefits include the reduction of drilling time owing to increased rate of penetration, less bit wearing, and the ability to handle fluid invasion. Among the numerous types of lightweight fluids used in drilling operations, foam appears as one of the most widely used. This is mainly because foam generates very low equivalent circulating densities while exhibiting good lubrication and hole-cleaning capacity, especially in vertical wells. It also offers a better control over the flow behavior of the phases involved within the well. To achieve success in drilling operations under this scenario, the understanding and design of properties affecting borehole hydraulics become major issues. Predictive models, chiefly for pressure profile, become even more imperative by the fact that common tools used for logging while drilling do not work properly when lightweight fluids are used, especially in offshore operations. Based on this, it is clear that the rheological characteristics of this compressible non-Newtonian fluid must be understood fully. Several researchers1-3 have studied foam-flow behavior in pipes in the past. However, there is no general agreement on the rheological description of the foam. The analysis of foam-flow behavior is rather difficult because of the number of variables involved, such as compressibility, flow geometry, foam generation, quality (ratio of gas-phase volume to foam volume), liquid- and gas-phase properties, slippage at the conduit's wall, and non-Newtonian behavior. It becomes even more challenging when annular flow takes place. Therefore, this study focuses on the experimental investigation of pipe and annular foam flow under elevated pressures and temperatures, with the objective of gaining a better understanding of how different variables affect the flow of this complex fluid. Capillary Viscometry. When a rheogram for a non-Newtonian fluid is available, it is possible, at least in principle, to predict the laminar-flow properties of such a fluid in conduits of simple cross section. The flow curve for a fluid can be rigorously and easily derived from pressure-drop and flow-rate data obtained with a capillary-tube or pipe viscometer of diameter D and length L.
An experimental investigation on polymer-based drilling foams was carried out. Rheology tests were performed with foams that have different concentrations of Hydroxylethylcellulose (HEC) and 1% commercial surfactant. Experiments were conducted in a large-scale flow loop that permits foam flow through 2", 3" and 4" pipe sections, and a 6"×3.5" annular section. During the experiments, frictional pressure losses across the pipe and annular sections were measured for different gas/liquid flow rates, polymer concentrations (0%, 0.25% and 0.5%) and foam qualities (70%, 80% and 90%). Significant rheological variations were observed between aqueous foams containing no polymers and polymer-thickened foams. Experimental data show three distinct flow curves for the 2", 3" and 4" pipe sections, which indicates the presence of wall slip. The Oldroyd-Jastrzebski approach was used to calculate the wall slip velocity and determine the true shear rate. It has been found that wall slip decreases as the foam quality or polymer concentration increases. Two foam hydraulic models, which use slip-corrected and slip-uncorrected rheological parameters, have been proposed. These models are applicable for predicting pressure loss in pipes and annuli. Model predictions for the annular test section are compared with the measured data. A satisfactory agreement between the model predictions and measured data is obtained. This paper will help to better design foam drilling and cleanup operations. Introduction The use of drilling foams is increasing because foams exhibit properties that are desirable in many drilling operations. In practice, aqueous and polymer-based foams have been used with commercial success. However, drilling foam rheology and hydraulics are still not sufficiently understood to minimize the risk and costs associated with foam drilling. It is generally accepted that the addition of polymers to the liquid phase affects the viscosity and stability of foams. However, the degree to which the bulk properties of drilling foams are enhanced by polymers has not been well understood and is difficult to predict. For safe and economical foam drilling, accurate knowledge of bottom-hole pressure is essential. However, foam rheology and pressure drop predictions are not accurate enough to provide adequate hydraulic design information such as equivalent circulation density.This problem is more pronounced when polymers are added, because the apparent foam viscosity of polymer-thickened foams can be significantly higher than aqueous foams. It becomes apparent that there is a need for polymer foam rheological characterization, in order to improve the knowledge of foam rheology and hydraulics. Foam rheological characterization was carried out using large-scale, single-pass pipe viscometers (composed of 2", 3" and 4" pipe sections). Foam qualities were varied from 70% to 90%. Test pressure and temperature were 100 psig and 80°F. Two foam hydraulic models were considered assuming:no-slip condition at the wall; andslip condition at the wall. The first model assumes no-slip boundary conditions in both pipes and annulus. By assuming no slip condition at the wall, slip-uncorrected foam rheological parameters were obtained from the pipe viscometer measurements. It has been found that if we plot friction factors versus Reynolds numbers for all test data, regardless of pipe diameters, foam qualities and flow rates, a single curve is obtained. This curve is similar to that obtained for incompressible fluid flow. Pressure drop in the annulus is calculated with the proposed model and satisfactory predictions are obtained. The second model is based on the assumption that there is wall slip in both pipes and annulus. Rheological parameters and wall-slip coefficient corrections were first obtained using Oldroyd-Jastrzebski approach. The annular pressure losses are predicted based on slip-corrected rheological parameters and wall-slip coefficient correlations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.