Laboratory investigations of paraffin deposition process and the remarkable changes in the crystal structure of waxes resulted in the development of several copolymer paraffin crystal modifiers. Their mixtures with surfactants have caused strong viscosity reduction in Various Vietnam high paraffin crudes. The changes in form and size of paraffin crystals due to co-crystallization between effective pour point-viscosity depressants and crude oil waxe s, were investigated and the results were recorded by means of scanning electronic microscopy (SEM). The mechanisms of pour point and viscosity reductions were examined using Infrared and Raman spectroscopes. The advantages and disadvantages of these tools were noted. Introduction The pour point and viscosity of crude oil are important physical properties. High pour point and high viscosity crude oil cause deposits at the critical wellbore, and in the tubing, flowlines and pipelines. Deposits in the wellbore reduce production. Deposits in pipelines can have disastrous consequences, both in lost oil and in environmental costs caused by pipeline ruptures. Waxy crude oils are also extremely difficult to transport in pipelines, especially in cold weather.[1,2] Various methods[3,4,5] have been designed to reduce the pour point and viscosity of high wax content crudes, including: thermal, and mechanical, and chemical methods, or a combinations of these methods. The use of chemical additives for pour point-viscosity reduction is receiving constant attention from researchers, with many improved formulations now available. Since no additive has proved universally effective, the selection of an efficient additive becomes critical, and a better understanding of the mechanism of crude oil pour point and viscosity reduction is extremely important. The purpose of this work is to study the mechanism of pour point and viscosity reduction of Vietnam crude oils such as White Tiger and Dragon using advanced analytical tools. Theory Of Pour Point and Viscosity Reduction Pour point reduction Numerous works[8,9] have shown that wax content and the molecular weigh distribution of waxes are primary factors in determing whether a crude oil has a high or low pour point. The additive used to reduce crude oil pour point must have the ability to change the crystalline state of wax during the crude oil cooling process. To form a paraffin crystal, a stable nuclei must first act as a growth center for the attachment of paraffin molecules. Certain chemicals are effective in inhibiting the growth of crystal by cocrystallizing or modifying the crystal or breaking up the molecular cluster. Other additives slow down the paraffin crystallization by coating the molecule of wax as it comes out of solution. Thusly, these additives can keep the paraffin in a liquid state. The first treating chemical group is polymers and copolymers, which inhibit or alter wax and crystal growth. They appear to work best in "water free" and low water content crudes. The second treating chemical group is surfactants that work best in the presence of water by water-wetting the paraffin flowline and pipelines.[10] The pour point depends on the shape and size of the crystal; any pretreatment which affects size and shape also effects the pour point reduction.[11,12]

The transportation of crude oil with high wax content through a submarine pipeline built without thermal insulation can cause serious problems. The heat loss due to the sharp temperature gradient between the crude and the environment results in the crystallization of wax in the crude, with a subsequent wax deposition on the walls of the pipeline. This can result in:reduction of the actual pipeline diameter resulting in higher pressure drops; and,the formation of gelled interlocking structures of wax crystals in the pipeline, leading to shutdowns. The safe and continuous operation of the pipeline has been dependent on the improvement in the flowability characteristics of the Vietsovpetro crude oils. Using pour point depressant chemicals can drastically reduce the potential risk for wax deposition and gelling. A study on the rheological properties of the crude oil enables an evaluation of different chemical types necessary to treat the crude. The pressure drop required to start pumping crude oil through newly constructed submarine pipelines or to restart the flow after an emergency production shutdown has to be determined. A pipeline model used to predict the restart pressures and flow characteristics has played a very important role in the technological concept and design of the product gathering system at Vietsovpetro oil fields. Introduction Currently, JV Vietsovpetro is operating three oil fields: Bach Ho (White Tiger); Rong (Dragon); and, Dai Hung (Big Bear). Crude oil is produced from fixed platforms, satellite platforms and MOU Daihung 1. After gas separation, the degassed oil is pumped to FSO for storage and subsequent export to shuttle tankers. Submarine pipelines carrying crude oil produced offshore encounters many more problems than land pipelines. The Vietsovpetro pipelines are generally laid on the seabed without thermal insulation. The temperature of the water at the seabed is in the range of 25°C to 28°C, with an occasional low temperature of 21.6 ° C. The transportation of a waxy crude having a pour point just 6 - 10 ° C higher than the seabed temperature can be associated with these problems:High cooling rates of the crude oil throughout the year;Wax deposition on the pipeline walls reducing effective diameters and increasing pressure drops(1,2,3); and,Buildup of a gelled interlocking structure of wax crystals at low temperatures and flow rates which may cause production shutdown. The pumping of waxy crude through a pipeline without thermal insulation can be facilitated using the following methods:Pumping crude oil conditioned by proper heat treatment. This involves pre-heating the waxy crude oil and heat tracing the pipeline to maintain the flow temperature above the pour point temperature of crude;Transporting crude oil mixed with water, i.e., in a two-phase flow transportation system;Pumping crude oil diluted with solvents or less waxy crude oil; and,Pumping crude oil treated with flow improvers. Conditioning by proper heat treatment can improve the fluidity of some crude oils, but this would require a huge heat generating plant on one of the offshore platforms in the field.

The performance of pipeline transportation of oil & gas mixtures can be optimized by different ways. This paper introduces a synergetic statistical approach based on field data to analyzing the oscillations of pressure by determining simultaneously Hausdorff's Dimension "D", Hurst's Index "H" and the Entropies "E", as a useful tool for managing the multiphase pipeline transportation systems. Introduction Practically, in most cases, the pipeline transportation of oil & gas mixtures encounters the fluctuation in pressures and flow rates that can cause the complexities and instability in the oil and gas production and gathering systems. To improve the transportation conditions and to provide adequate safety for working pipelines the studies on implementation of a new approach to analyzing the dynamical system have been carried out. The results obtained in studies allow diagnosing the hydro-dynamical states of oil and gas flows in pipelines and its ordering. Consequently, it can help to transport the oil and gas mixture through existing pipelines at maximum flow rate but with minimum pressure losses. Background One of most important missions in pipeline transportation of oil and gas mixture is to improving hydraulic regimes based on forecasting the dynamical conditions. This may be achieved by regulating the flow regime or elimination of phase inhomogeneity of flows in the pipeline. The most effective way to settle the problems is to establish the principally new technologies allowing optimizing the solutions at minimum expenses for their practical realization. Transportation of production at maximum flow rate with minimum spending the energy through submarine pipelines represents the most important duty in operation of oil and gas pipeline network in offshore conditions for JV Vietsovpetro. Necessary condition for solving this dilemma is to operating the pipelines at lowest level of pulsation and minimum hydraulic losses. This may be executed by preliminary gas separation from oil or excluding most of resources influencing on stability of dynamical state of system. In conjunction with this, the execution of field experiments in working pipelines would require unproductive expenditures of finance as well as time. More and more attention is paid on development of method diagnosing the state of an object using data collected during routine operation. Accidental fluctuations, occurring in hydraulic systems, often have determined character. They happen due to own system and can serve as resource of information on internal characteristics. The existence of factors affecting on stability of working regime in pipeline, such as: gas flow rate ratio, flow rate, pipe size, depositions, leads to occurrence of oscillatory movement that heap on pulsations of pressure and flow rate. Meanwhile, they change the spectra and other characteristics of initial noises. So that the analysis of pulsations allowing finding out those changes, can lead to diagnosing the degree of inhomogeneity of being studied system. Because the oscillations of pressure and flow rate have more significant chaostic character, hence for their analysis the latest achievement in the theory of dynamical chaos is to be involved.

In production and transportation of waxy crude oil as well as in practical Rheological studies of non-Newtonian liquids, it is very important to find and characterize its thixotropic properties. There are some ways to study this phenomenon, but nowadays the existing equations still can not quantifiably describe the time-dependent behavior of thixotropic liquids with acceptable accuracy using in this case an exponential or hyperbolic functions. The authors have conducted the screening studies on rotational viscometer Rotovisco RV-20 with different kinds of waxy crude oils from JV "Vietsovpetro" fields offshore Vietnam. Based on the received experimental data and its analysis the authors have proposed a new equation showing a very good agreement between experimental and calculated data (the average deviation is less than 2%). The general time-dependence of shear stress at constant shear rate can be much more precisely expressed. A new idea "the measure of thixotropicity" of liquids at given shear rate and temperature is also proposed to characterize the properties of thixotropic liquids.

Here generalized analysis is given for transport of highly paraffin and highly congealing oil taking into account layout, technology of transport and construction features of subsea oil pipeline. In accordance with results of physical experiments for active oil pipelines the generalized mathematical model was made to explain thermohydrodynamic regime of telescopic construction oil pipe operation for paraffin and highly congealing oil transport. Thermohydrodynamic and mass exchange process in subsea pipelines are explained by differential equation system:flowcontinuityenergyheavy hydrocarbon fraction concentration forming wall depositionsadsorbtion kinetic and hydrodynamic desorbtion of wall oil depositions Based on mathematical model of existing subsea oil pipeline, new computer method was created for analysis of thermohydrodynamic and technological process while transporting highly paraffin and highly congealing oils. There was developed respective software package allowing to study both steadied and unsteady transport process in wide range of thermobaryc and technological parameters change characterizing oil pipeline operation. Proposed method of analysis is intended for designing of new pipelines and modification of old subsea oil pipelines and change of transport technology in active pipelined, i.e. optimization of transport parameters and determination of oil pipeline safe operation limit eliminating critical transport regime-telescopic pipeline "freezing". Digital experiments have shown that in certain technological transport condition the critical operation regime starts proceeding from intensive heavy hydrocarbon depositions (in solid phase) at inside pipeline surface. It is accompanied by spontaneous (uncontrollable) decrease (due to hydraulic resistance) of pipeline throughput. This process (if timely special measures are not taken) will result in full transport stoppage and subsequent pipeline "freezing". Based on analysis of different technological parameters influence on thermohydrodynamic pipeline operation regime, there were considered and proposed method of thermal, hydrodynamic and chemical influence on wall depositions which allow to eliminate critical pipeline operation regime at different flow rates. Here the results are given for digital simulation of pipeline operation in form of diagrams. Introduction World pipeline experience shows that intensive heat exchange between transported oil and environment in subsea pipelines leads to sharp change of thermohydrodynamic process (characteristics) in flow along the pipeline [1–5,11]. Oil temperature drop in flow direction cause change of its rheologic properties and is accompanied by phase transition as well as formation of oil wall depositions at pipeline internal surface. The above factors at certain technological conditions appear to cause gradual spontaneous reduction (due to flow hydraulic resistance) of pipeline flow rate. Ant if timely special measures are not taken it can lead to full stop of pumping with subsequent pipeline congealing (freezing). The above specific peculiarities of pipeline operation raise the problem of special technology development for high-paraffin and high-congealing oil transportation that should exclude possibility of this critical process occurrence during transportation. Higher paraffin plays significant role in oil recovery and transport process. Here and after paraffin means alkane C17H36 and higher solidifying at normal temperature. Content of individual higher alkanes in oils, e.g. White Tiger and Dragon oil-fields, ranges from 1.3 to 4.6%. Its density in solid phase is 865.0 – 940.0 g/cm3 and in melt phase - 777 – 790 g/cm3. Depending on alkanes temperature and concentration, alkanes in oil can be in dissolved or crystallized state. Normal alkanes have low boiling temperature and molecular mass. They can form large crystals. Isoparaffin and cycloparaffin have higher molecular mass as compared to normal ones. At certain conditions they can form monocrystals.