Hot Crude Oil Research Articles

Investigation into the heat transfer models for the hot crude oil transportation in a long‐buried pipeline

AbstractBased on reasonable simplifications of a two‐dimensional (2D) energy equation, a basic heat transfer equation in 1D form is obtained for the hot crude oil transportation in a long‐buried pipeline. To enclose the heat transfer equation, the overall heat transfer coefficient and the numerical simulation of temperature fields of pipe wall and soil are introduced, and they together with the basic heat transfer equation constitute 1D and cross‐dimensional heat transfer models of crude oil transportation, respectively. Some numerical procedures, including grid generation, partial differential equation discretization, and algebraic equation solution, are combined to solve the two heat transfer models. Based on the designed cases with different pipeline parameters, the relative deviation between the numerical results from the two heat transfer models does not exceed 1%, and the two heat transfer models agree well. Furthermore, the nonuniform natural soil temperature field is designed, and its influence on the oil temperature and the deviation of the 1D heat transfer model is investigated. Under the condition of the nonuniform natural soil temperature field, the atmospheric temperature as the ambient temperature in the 1D heat transfer model causes an apparent deviation, whereas the soil temperature at the buried depth of the pipeline in the natural soil temperature field as the ambient temperature does not. This study can provide a reference for the reasonable selection and use of the heat transfer models of the buried hot oil pipeline.

Heat-Transfer Characteristics of Subsea Pipelines Embedded in Multilayered Soils

Summary A good pipeline design must ensure that the heat loss is small enough for flow assurance despite unfavorable hydrate and wax depositions. The objective of this study is to experimentally verify a formula for the modified overall-heat-transfer coefficient (OHTC) that considers multilayered soil conditions for steady-state subsea pipelines. A laboratory-scale experiment is conducted to simulate the flows of cold seawater and hot crude oil inside the pipes immersed in multilayered soils at nine burial-depth rates. The obtained results are in good agreement with the data obtained by a previously derived OHTC analytical formula.

Study on Low Flow Rate Operating Characteristics of Hot Waxy Crude Oil Pipelines Based on an Unsteady-State Calculation Method

Hot crude oil pipeline operated at low flow rate might work in an unstable state, where the friction loss continuously increases with the decreasing flow rate. This will lead to harmful flow stagnation and needs proper management. In this paper, the unsteady-state thermal-hydraulic behavior of the coupled pipeline-pump system is investigated by adopting an unsteady-state numerical model instead of the traditional steady-state model. The new model considers the impacts of the heating strategies, initial operating conditions, and pump characteristics on the pipeline characteristics at low flow rate. Through obtaining the transient characteristics of the flow rate and friction loss, the stable and unstable working ranges are distinguished and critical flow rate is calculated. It is shown that the transient characteristics at low flow rate can be classified into three categories. (1) The flow rate keeps constant for the initial period and then decreases continuously while the friction loss increases monotonously. (2) The flow rate is constant while the friction loss increases firstly and then stays stable. (3) The flow rate maintains constancy while the friction loss increases firstly and then decreases to a final stable level. Besides, it can be concluded that the critical flow rate calculated by the unsteady-state method is recommended with preheating before the flow rate drop.

Analyses on Heating Energy Saving of Two Hot Waxy-Crude Oil Pipelines Laid Parallel in One Ditch

Laying two pipelines in one ditch is a new technology recently employed by the petroleum companies of China and has great advantages of minimizing environmental disruption as well as bringing tremendous economic and social benefits. In this study, by means of numerical simulations analyses are carried out to evaluate heating energy saving for the operation of two hot crude oil pipelines laid parallel in one ditch. Comparisons are made based on three various operating scenarios, among which the best operation is proposed. The effects of some important parameters such as the gap between the two pipelines (also called pipeline interval) and pipe length are investigated. It is found that two hot crude oil pipelines laid parallel in one ditch can dramatically save heating energy when compared with two pipelines laid, respectively, in two separate ditches.

Novel Arrangement of Rough Tubes for Heat Flux Improvement

The objective of the research is to represent a novel arrangement of conical three dimensional rough tubes (FS3D) for heat transfer coefficient enhancement. Experiments were performed with 316 stainless steel tubes of FS3D roughness and hot crude oil was circulated in constant heat flux condition in the related set up. The pressure drop is measured in this set up and compared with the pressure drop in a smooth tube with the same operating conditions. The heat transfer coefficient is one of essential parameters for design of heat transfer equipments and in this experimental work this is investigated for an Iranian crude oil in the FS3D rough tube. The heat transfer coefficient in FS3D rough tubes is higher than in other commercial enhanced tubes. FS3D rough tubes improve the performance of heat transfer equipments and also optimize the size of the mentioned devices. Consequently this type, the FS3D rough tube, is advantageous in energy and cost saving.

Numerical simulation of a buried hot crude oil pipeline under normal operation

A physical model is proposed to study the heat transfer and oil flow of a buried hot oil pipeline under normal operation. With certain physically reasonable assumptions, the governing equations for the thermal analyses are derived. An approach combining unstructured-finite-volume [1] and finite difference methods is applied to solve the governing equations, in which the soil domain was discretized by unstructured grids. Numerical simulations in a wide range of operating conditions are conducted. The operating conditions cover 5 months (April, May, June, October and November) with throughputs ranging from 15,007 tons per day to 27,451 tons per day and outlet temperatures varying from 40.6 °C to 64.8 °C. Measured data are provided for comparison. A good agreement between numerical simulations and field measurement suggests that the proposed numerical scheme is a suitable method to simulate the heat transfer and oil flow of buried hot crude oil pipelines. We also analyze a number of influential factors on the temperature distribution of oil along the pipeline.

Numerical simulation of a buried hot crude oil pipeline during shutdown

In this paper a mathematical model is built for a buried hot crude oil pipeline during shutdown, and an unstructured grid and polar coordinate grid are respectively applied to generating grids for the soil region and the three layers in the pipe (wax layer, pipe wall, and corrosion-inhibiting coating). The governing equations are discretized using the finite volume method. The variations in temperatures of static oil and soil were investigated during pipeline shutdown in both summer and winter, in which some important parameters of the soil and crude oils of a Northeast pipeline are employed.

Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution

AbstractIn petroleum refineries, water is used in desalting units to remove the salt contained in crude oil. Typically, 7 % of the volume of hot crude oil is water, forming a water‐and‐oil emulsion. The emulsion flows between two electrodes and is subjected to an electric field. The electrical forces promote the coalescence of small droplets of water dispersed in crude oil, and these form bigger droplets. This paper calculates the forces acting on the droplets, highlighting particularly the mechanisms proposed for droplet–droplet coalescence under the influence of an applied electric field. Moreover, a model is developed in order to calculate the displacement speed of the droplets and the time between droplet collisions. Thus, it is possible to simulate and optimize the process by changing the operational variables (temperature, electrical field, and water quantity). The main advantage of this study is to show that it is feasible to increase the volume of water recycled in desalting processes, thus reducing the use of freshwater and the generation of liquid effluents in refineries.

Thermal impact of the products pipeline on the crude oil pipeline laid in one ditch – The effect of pipeline interval

Numerical simulations are carried out to study the thermal impact of the cold products pipeline on the hot crude oil pipeline of the steady state. The pipelines studied are those used in the West Pipelines in China. The physical properties of North Xinjiang crude oil and those of 90# gasoline were used in this study. The effect of pipeline interval on the thermal impact is studied in details at various conditions.

A Laboratory Study of Combustion Override Split-Production Horizontal Well (COSH) Process

Abstract A 3D physical model has been developed to investigate the Combustion Override Split-Production Horizontal well (COSH) process. The 3D model is a rectangular box with dimensions of 18 cm by 54 cm by 12 cm. The vertical well was used as an air injection well and the top horizontal well was used to collect the gases generated by the combustion process. A horizontal production well was placed near the base of the model to collect hot crude oil and water. A total of eight experiments, six of dry combustion and two of wet combustion were conducted to investigate the process parameters. Forty-eight thermocouples were used to obtain 3D temperature profiles in the vertical and horizontal mid-planes. Combustion peak temperatures up to 450? C were recorded, with oil recoveries exceeding 40% OOIP for the single vertical producer well case. The recovery using a horizontal producer placed at the base of the model was 65% OOIP, higher than the vertical producer. The COSH process was performed to combine the beneficial features of gravity drainage and horizontal production wells. A hot gas chamber was formed around the vertical injection well similar to the steam chamber in the SAGD (Steam Assisted Gravity Drainage) process. In the COSH process the hot gas chamber consisted of steam, injected gas, and combustion gases. Gravity drainage was the principal mechanism for moving heated oil to the horizontal production well in the COSH process. Introduction In-situ combustion is a commercial process for recovering heavy oils. In this process, air or more generally an oxygen containing gas is injected into a formation containing viscous oil. A burning front supported by air injection is created and subsequently propagated through a reservoir. The burning front travels in the same direction as the injected air (forward combustion) or counter to the direction of air (reverse combustion). The high cost of air compression for dry forward combustion is one of the major factors that influences the economics. Therefore, the oil industry introduced a new concept that is water injection with air into the reservoir to improve the thermal efficiency of the process. Another important advantage of wet combustion is less fuel consumption compared to dry combustion. The technology of horizontal wells for the production of crude oil from conventional and heavy oil reservoirs and tar sands has been implemented successfully in many fields. Extensive work has been carried out to develop horizontal drilling techniques to increase direct contact between wellbores and pay zones in order to improve productivity and recovery. Thin reservoirs, reservoirs with vertical fractures and in reservoirs where low productivity has been observed with vertical wells, due to water or gas coning positive results and improved recovery is provided by the application of horizontal well technology. Until now, most laboratory experiments of in situ combustion have been conducted using combustion tubes whose results are then used for field applications. The two important parameters that must be understood before field application, are sweep efficiency and combustion front stability, which cannot be obtained from combustion tubes due to their one dimensional geometry.

Design of a Submarine Oil Pipeline

Submarine oil pipelines carry hot crude oil obtained from offshore oil wells to an onshore location. As the flow proceeds, the crude oil progressively cools down, drastically changing its kinematic viscosity. This cooling increases the surface resistance to flow considerably. Analysis of such a pipeline is complicated because it involves a large number of variables representing fluid, flow, thermal properties, and geometry. Furthermore, as the liquid cools down the flow may change from turbulent to laminar. This paper reports a unified friction factor equation valid in laminar as well as in turbulent flow that deals with this complex flow situation. This equation can aid development of a methodology for analysis and design of offshore pipelines.

Response of Microorganisms to Hot Crude Oil Spills on a Subarctic Taiga Soil

This study was conducted on the short-term effects of seasonal spills of hot Prudhoe Bay crude oil on microorganisms in a taiga soil in interior Alaska. Following a winter spill, the filamentous fungal populations were inhibited whereas the heterotrophic bacterial populations were stimulated. After a summer spill there was an initial depression of both the filamentous fungal and bacterial populations followed by a general enhancement. In both oil spill plots, yeasts; along with the denitrifying, proteolytic, oil-utilizing, and cellulose-utilizing microorganisms; were favorably affected by the oil. Soil respiration was also enhanced in the oiled plots. An extended period of study is required to fully evaluate the impact of oil on the soil microflora and the role of these microorganisms in recovery of oil-inundated areas in subarctic ecosystems.

The Continuous Spilling of Hot Oil on Ice

Abstract The continuous spilling of hot Norman Wells crude oil onto an ice surface was investigated with oil temperature, ice temperature and spilling rate as parameters. An equation for spreading of the oil was developed in whick the oil slick area, A, was proportional to t(1,2), where t is the elapsed time. Experimental data showed that A was prow portional to t0.8. Increases in both oil and ice temperatures were found to cause an increase in A, and temperature effects could be taken into account by relating kinematic viscosity to a function of the geometric mean of the ice and oil temperatures. Introduction ALTHOUGH the spreading of hot oil on ice is of interest from the point of view of oil spills in Arctic regions, no controlled quantitative study taking several variables into account has been published. In previous work, Chen et al.(1) studied the instantaneous release of oil under controlled isothermal conditions, and Glaeser(2) and McMinn(3) carried out non-isothermal field tests under a single experimental condition. The present work concerns the continuous spilling of hot crude oil on ice at ice temperatures down to −40 °C and oil temperatures up to 60 °C. Continuous spilling would occur in the event of a pipeline leak. The oil and ice temperatures chosen cover likely pipeline conditions during the Arctic winter. In common with the previous work(1), crude oil from commercial production at Norman Wells, Northwest Territories, Canada, was used. Mackay, Charles and Phillips'" have discussed other aspects of the physical behaviour of crude oil in Arctic environments, with particular reference to Norman Wells crude oil and the Mackenzie Valley of the Northwest Territories. Theoretical Background It has been recognized(1–3, 5–7) that the spreading of a liquid over a solid surface passes through three distinct regions: gravity-inertia, gravity-viscous and surface tension-viscous. However, in continuous spreading, the gravity-viscous region is of primary importance because surface-tension spreading is not likely to occur due to the continuous flow, and the gravity-inertia spreading, which occurs only in the area around the point of deposition, will not be observed. Using the same argument as that used by Chen et al.(1), the gravitational outward pressure force per unit volume is (Equation Available In Full Paper) In application of this model to the non-isothermal case of spreading of hot oil on ice, it should be noted that µ (or υ) must represent an effective viscosity, as there is a temperature gradient across the spreading oil film; any correlation of data in terms of equation (5) will therefore be in terms of such an effective viscosity. This notion is further reinforced by the observation that the spreading of hot oil on ice must of necessity involve flow of oil over a water film formed from the ice at the interface with the hot oil.

Insulated Hot Oil-Producing Wells In Permafrost

An analysis is presented for the transient heat flow in and around production wells in which insulated casings may be used to reduce production wells in which insulated casings may be used to reduce permafrost thaw in the Alaskan North Slope. Results show that insulated permafrost thaw in the Alaskan North Slope. Results show that insulated casing systems can greatly restrict potential thawing of permafrost. Introduction A potential problem in the production of hot (180 to 200 degrees F) crude oil in unprotected wells on the Alaskan North Slope is the thawing of permafrost adjacent to the wells. Thawing of permafrost could result in soil consolidation, subsidence, and possible damage to the well. BP Alaska, Inc., and Arthur D. Little, Inc., have collaborated in developing a method to analyze the thermal performance of insulated wells in permafrost and in performing analyses of typical insulated well-casing systems. The ultimate objectives of this work were to understand permafrost thermal behavior under oil production conditions and to assist the design, development, and testing of an insulated well-casing system. The heat flow along and through the well casing and into the surrounding soil is quite complex. Standard, closed-form, or integral solutions available for melting in one or two dimensions are not applicable to the heat flow in the surrounding soil because of the complexity of heat exchange between the flowing hot oil and the ground, and the variation of thermophysical properties with temperature and depth. Previous studies for wellbore heat transmissions have neglected vertical beat flow in the soil and have not taken into account the effects of latent heat of fusion. Couch et al. have developed a mathematical model for thawing the soil surrounding unprotected wells that included the effects of latent heat of fusion of the soil. The effects of the latent heat were shown to be significant. Their analysis treated the well casing as part of the thermal resistance between the hot oil and the soil. Heat flow along the casing was not accounted for. In the present analysis, we have considered the details of the construction of the casing itself, as well as the heat flow in the casing, to evaluate the effects of "thermal shorting" across the insulation where casing joints are coupled. In addition, the model allows an examination of the effects of localized failure of one or several insulation joints. Analysis Problem Definition and Mathematical Models Problem Definition and Mathematical Models Fig. 1, a sketch of a typical configuration oil-producing well in a permafrost region, shows the flowstring for hot crude oil, a surrounding insulation system (extending only over a selected depth of the permafrost region) and casing, and a region of cement surrounding the well casing. Hot crude oil enters the flowstring at a depth significantly below the permafrost level and flows upward, transferring heat to the innermost pipe by convection. Heat is conducted along the pipe by convection. Heat is conducted along the flowstring, through the casing and insulation, through the cement, and into the surrounding permafrost and unfrozen soil. Since the well-casing components provide a thermal short circuit in the vertical direction, heat also may be conducted along the casing from warmer to colder regions. JPT P. 357