T his work is aimed to study the wax deposition process on the internal surface of oil production pipelines and the influence of parameters such as flow rate and pipe wall temperature on the deposit thickness for a light crude oil with high paraffinic content considering three different temperature boundary conditions on the pipe wall; two of which assumed a profile temperature on the boundary, fact that has not been considered in previous works, and the third a constant value. The analysis was conducted assuming pseudo steady conditions on the fluid phase. The finite differences method was applied to solve the differential equation system and the solution was implemented numerically using the C++ programming language. The model was validated with the experimental results reported by Singh et al. (2000) and subsequently used to simulate the growth of the paraffin deposits as a function of flow rate and pipe temperature. The results showed that increased flow rates reduce the maximum deposit thickness, as it spreads on a longer distance in the pipe when considering a constant wall temperature or the axial thermal gradient with a positive slope, and the opposite effect is observed when considering the axial thermal gradient with a negative slope. E sse trabalho objetiva estudar o processo de deposição de parafinas sobre a superfície interna dos tubos de produção de petróleo e a influência de parâmetros como a velocidade de fluxo e a temperatura da parede sobre a espessura do depósito para um petróleo leve com alto conteúdo parafínico considerando três condições fronteira sobre a parede do tubo; sendo que dois delas pressupõem um perfil de temperatura na fronteira, fato que não foi considerado em trabalhos anteriores, e a terceira um valor constante. A análise foi feita com a presunção de condições pseudo-estáveis na fase fluida. O método de diferenças finitas foi aplicado para a resolução do sistema de equações diferenciais e a solução foi atingida de forma numérica utilizando a linguagem de programação C++. O modelo foi validado com base nos resultados experimentais relatados por Singh et al. (2000) e posteriormente utilizados para a simulação do crescimento dos depósitos de parafina como uma função da velocidade de fluxo e da temperatura do tubo. Os resultados demonstraram que o aumento da velocidade de fluxo reduz a espessura máxima do depósito, no entanto, ele se estende sobre uma distância maior sobre o tubo quando considerada a temperatura de parede constante ou o gradiente de temperatura axial com inclinação positiva; enquanto se verifica o efeito contrário quando considerado o gradiente de temperatura axial com inclinação negativa. E l objetivo de este trabajo es estudiar el proceso de deposición de parafinas sobre la superficie interna de las tuberías de producción de petróleo y la influencia de parámetros como la velocidad de flujo y la temperatura de la pared sobre el espesor del depósito para un crudo ligero con alto contenido parafínico considerando tres condiciones de frontera sobre la pared de la tu...
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractBarite sag is a significant variation in mud density caused by the settlement of barite or other weight material in high-angle wells. The wide fluctuations in mud weight can lead to severe operational problems, including well-control, induced wellbore instability, downhole mud losses, and stuck pipe.A laboratory flow loop has been used to evaluate the influence of key drilling parameters on barite sag. Results show that the highest sag occurs at angles in the region 60-75°, particularly at low annular velocities. Drillpipe rotation is shown to be particularly beneficial in minimising barite settlement. Rotation also assists in re-distributing barite deposits formed on the low side of the hole. Data from the tests clearly demonstrate the interdependence of drillpipe eccentricity, rotation, and mud flow rate.Results from the study have been combined with field observations to develop guidelines to minimise barite sag and manage the associated risks. The conclusions of the study are that barite sag can be minimised by attention to detail at the planning and execution stages of drilling a well. In particular, recommendations in four key areas are addressed: well planning, mud properties and testing, operational practices, and wellsite monitoring procedures.
IADC Members Abstract Optimization of hole cleaning remain. one of the major challenges when planning and drilling high angle and extended reach wells. in this paper, a simple rig-site graphical technique is presented for determining hole cleaning requirements for a range of hole sizes. This method uses a set of charts which have been derived from a computer model based on both laboratory and field measurements. Access to the technology at the rig-site has been greatly improved by the development of the simplified charts. Examples are presented which illustrate how the charts can be applied to determine the influence of the major drilling variables on hole cleaning requirements. Mud rheology is shown to be a key variable for optimising hole cleaning in deviated wells. The charts can also be used to quantIfy the effect of hole enlargement which adversely affects hole cleaning. In addition, the paper discusses the detailed methodology behind the development of the charts from the original physically-based model. The charts presented in the paper are valid for the typical North Sea drilling conditions. Introduction When planning or drilling a deviated well, one of the key parameters which must be determined is the minimum flow rate required to transport drilled cuttings up to surface and keep the the hole clean. This minimum flow rate is called the critical flow rate (CFR). If inadequate flow rate is used, cuttings will settle on the low-side hole and form a large stationary bed which may result in severe drilling problems such as high drag and torque, hole packing-off and stuck pipe. All these may subsequently require expensive remedial operations and thus incur substantial increases in drilling cool, It Is crucial to know the CFR when planning and drilling a deviated well so that the adequate and economical drilling equipment can be selected and optimum parameters determined. This has become Increasingly Important over recent years as the demands of field developments have dictated more higher angle and extended-reach wells. Hole cleaning has been investigated by numerous researchers. In the early studies, the effects of a range of variables on cuttings transport and bed formation In deviated wells were investigated. The later studies have tended to concentrate upon developing mathematical models for predicting the CFR. Most of the models have been based on small-scale experiments. In a previous paper, a physically based model for predicting the CFR in deviated wells was pressed. This was developed based on the analysis of forces acting upon the cuttings and the associated dimensionless groups. The model was validated initially with experimental data obtained from an r wellbore simulator, and further validated with actual drilling data from six different sized holes from 8-½" up to 17-½". In this paper a set of charts is presented. These can be used by drilling engineers at the rig-site to optimise hole cleaning for drilling various hole sections of a deviated wall. P. 499^
A joint industry project was established to study barite sag mechanisms and to develop field guidelines to manage the consequences. A simple empirical model was developed to compare sag potential for a wide range of fluid types. In the study, physical properties of the mud, wellbore conditions, and characteristics of the weighting material were shown to have a large influence on sag behavior. The study also included direct measurements of the properties of settled weight-material beds. These results provide new insight into the mechanisms of barite sag and how best to manage problems in the field.Data from the tests clearly demonstrate that the parameters affecting sag are interrelated and seldom act in isolation. For all muds tested, the highest sag occurred at low annular velocities over angles from 60 to 75°. Drillpipe rotation was particularly beneficial in minimizing barite settlement. Rotation also assisted in re-distributing barite deposits formed on the low side of the hole.The improved understanding of the mechanisms of barite sag enabled development of practical field guidelines. Case history studies presented in the paper demonstrate how the results of the work together with better field monitoring have been successfully applied to manage the effects of barite sag in high-pressure/hightemperature and extended-reach drilling operations.Test Fluids. The 20 test fluids represented a variety of mud types, formulations, weights, suppliers, and geographical sources. One of the project goals was to select muds from active directional wells ͑Ͼ30°͒ using weighted muds ͑Ͼ12 lbm/gal͒ in order to provide immediate feedback to operations. No other stipulations were made on field muds. Some laboratory-modified and laboratory-prepared fluids were also tested. Physical properties of all test fluids are listed in Tables 1 and 2. Mechanical-Parameter Results. Fig. 3 shows results for Mud 6 using the standard protocol at four inclinations ͑45, 60, 75, and 90°͒. Circulating fluid density change ͑corrected to 120°F͒ is plotted vs. time. All fluids tested responded similarly although the magnitudes varied.Most, if not all, of the sag-bed formation occurred at low flow rates and no rotation. Initial pipe rotation to 75 rpm consistently had the greatest effect on removing the beds. Doubling the rotary speed and then the annular velocity helped as expected, but to a much lesser extent.Time-segment 3 in Fig. 3, during which the sag was greatest, most clearly demonstrates the effects of angle. For Mud 6, the order of decreasing sag severity was 60, 45, 75, and 90°. While each individual mud tested exhibited slightly different behavior, the angle at which the maximum sag occurred was consistently in the range 60 to 75°. This is consistent with previously reported data. 3Fluid-Parameter Results. Rheology, density, weight material, and chemical treatments were the key fluid parameters investigated. These parameters emerged from an earlier study as the most significant variables affecting sag that can easily be controlled in the fie...
A new physically based model is described in this paper which has been developed based on the analysis of forces acting on the cuttings and the associated dimensionless groups. The model can be used to predict the critical (minimum) flow rate (CFR) required to remove, or prevent the formation of, stationary cuttings beds on the low-side of the wellbore in deviated wells. The model has been validated with the experimental data obtained from an 8″ wellbore simulator located at BP Research Centre Sunbury, and with field data from 8-1/2″, 12-1/4″ and 17-1/2″ holes. By using the model, the effects of major drilling variables on cuttings transport are evaluated and compared with experimental and actual field data. The results show that the model accurately predicts the effects of the major variables such as: hole angle, penetration rate, mud properties and flow regime. In particular, the model provides a mechanism to support the use of both low and high viscosity pills, and mud low-shear enhancers - which have been widely used during drilling operations to improve hole cleaning. The model has been incorporated into a computer program which can predict the CFR under the specified drilling conditions. A series of simplified hole cleaning charts have also been developed which enable the optimum hole cleaning parameters to be determined at the rig-site.
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