Crude Oil Emulsions

Much of the oil produced worldwide is accompanied by water in an emulsion that requires treating. Even in those fields where there is essentially no initial water production. Technical Data used in the field explained in petroleum courses in Islamabad. water cuts may increase in time to the point where it is necessary to treat the emulsion. Water content of the untreated oil may vary from a fraction of I % to over 90%. To prevent increased transportation costs, water treatment and disposal costs, and deterioration of equipment, purchasers of crude oil limit the basic sediment and water (BSSCW) content of the oil they purchase. Limits vary depending on local conditions, practices. and contractual agreements and typically range from 0.2 to 3.0%. BY&W is usually predominantly water but may contain solids.

The solids contained in the BS&W come from the producing formation and consist of sand. silt, mud, scale. And precipitates of dissolved solids. These troublesome solids vary widely from producing field to field. zone to zone, and well to well.

Purchasers may also limit the salt content of the oil. Removing water from the stream decreases the salt content. Salt content along with BS&W are the two important crude purchasing requirements. Some more details of petroleum courses in Islamabad are as under.

An emulsion is a heterogeneous liquid system consisting of two immiscible liquids with one of the liquids intimately dispersed in the form of droplets in the second liquid. An emulsion is distinguished from a simple dispersion of one liquid in another by the fact that, in an emulsion, the probability of coalescence of droplets on contact with one another is greatly reduced because of the presence of an emulsifier, which inhibits coalescence. Such inhibition is not present in a dispersion.

The stability of the emulsion is controlled by the type and amount of surface-active agents and/or finely divided solids. which commonly act as emulsifying agents or emulsifiers. As shown in Fig. 19.1, these emulsifying agents form interfacial films around the droplets of the dispersed phase and create a barrier that slows down or prevents coalescence of the droplets.

The matrix of an emulsion is called the external or continuous phase. The portion of the emulsion that is in the form of small droplets is called the internal, dispersed, or discontinuous phase. The emulsions considered in this chapter consist of crude oil and water or brine produced with it. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.

Procedure for Typical Measuring, Sampling, and Testing

The procedure given here is the API method currently in effect for running a field tank of crude oil. Since there are many variables that would alter this method, this procedure is applicable on/~) under specific conditions. Technical Data used in the field explained in petroleum courses in Islamabad.   The tank is vertical, no pressurized, fixed roof with side outlets, and it is to be gauged by the innate method. The oil is less than 100 seconds at 100°F (Saybolt universal viscosity) and is a liquid at atmospheric temperature and pressure.

 A cup case thermometer is used to read temperature of the oil in the tank.. A thief is used to obtain fluid samples from the tank.. The API gravity scale hydrometer test method is used to determine the API gravity of the oil; the temperature of the oil has to be near 60°F (* 5°F).. The water and sediment in the oil is to be determined by the centrifuge method with a 203-mm [8-in.] cone-shaped tube. Some more details of petroleum courses in Islamabad are as under.

The following outline gives the sequence of steps to betaken and the key points to be noted at each step. . Isolate the tank to be checked.. Use face mask and fresh air bottles if H2S hazard exists.

 Ground your body to stair railing or tank shell before reaching the top. This prevents static electrical discharge in a hazardous area. . Stand to the side of the hatch when opening to permit wind to blow gas away from face.. Measure temperature. Suspend thermometer in oil tank. Thermometer should be 12 in. or more from tank shell and must be immersed in oil for 5 minutes.

Use an ASTM-approved, wood-back or corrosion resistant metal cup case. If atmospheric temperature differs by more than 20°F from that of the liquid in the tank, the cup case should be given at least two preliminary immersions. Empty the cup case after each  immersion. Rapidly withdraw the thermometer and read and record the temperature to the nearest 1°F. Note: The number of temperature measurements varies with the depth of the liquid. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.

Dehydration by Adsorption.

Water vapor also can be removed from natural gas by use of a solid desiccant as an adsorption medium. The adsorption process is a very complex phenomenon involving transfer of the component adsorbed from the gas phase to contact with the solid. Technical Data used in the field explained in petroleum courses in Islamabad.

For this reason the most effective adsorbents have extremely large surface areas per unit of mass. This means that their surface is honeycombed with capillaries that serve to provide the necessary surface area. A flow sheet of a typical dry desiccant dehydration unit is shown in Fig. 14.22. There must be at least two desiccant beds for continuous operation because adsorption is a batch process. The main gas stream flows through an inlet separator where all free liquids are removed. Any liquids can be harmful to the dehydration process. Free water will reduce the capacity of the unit if not removed.

Hydrocarbons can poison the bed if not properly regenerated. The main gas stream then flows through a pressure-reducing valve that controls the flow of the regeneration gas by inducing a pressure drop in the main gas stream. The gas then flows through one of the two adsorption towers where it contacts the desiccant and the water vapors are removed. The main gas stream flows to the sales gas line through a gas-to-gas heat exchanger where heat is removed from the regeneration gas. Some more details of petroleum courses in Islamabad are as under.

The second adsorption tower is regenerated while the other tower adsorbs water vapor from the main gas stream. Regeneration gas (approximately 10 to 15% of the total gas flow) is taken from the main gas stream upstream of the pressure reducing valve and passed through a heater where the temperature is raised to approximately 450°F. The hot gas then passes through the desiccant bed.

The water adsorbed through the bed is vaporized and swept out of the bed by the regeneration gas. The hot, wet regeneration gas passes through the gas-to-gas exchanger where it is cooled by the main gas stream. The water condensed from the gas is separated in the regeneration gas scrubber. The regeneration gas flows into the main gas stream downstream of the pressure-reducing valve. Because of the regeneration gas flow, the pressure drop through a solid desiccant dehydration unit will be higher than for a TEG unit and will be approximately 25 psi for the system. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.

Gas-Treating Systems for Removal of Water Vapor, Cot, and H2S

Natural gas can contain any number of no hydrocarbon impurities in the formation or at wellhead conditions. Some of these are detrimental to efficient pipeline operation,  whereas others have no effect on operation but do affect the heat content or Btu rating of the natural gas. Technical Data used in the field explained in petroleum courses in Islamabad.

In almost every case natural gas contains water vapor to some extent. The characteristics of the rock in the formation will determine largely the extent to which water occurs. In some cases the gas is supersaturated, which means that free water will be present. In other cases the gas is saturated at reservoir conditions, which would mean that at producing conditions it will be supersaturated. Finally, the water content can be much lower than saturation but higher than specifications to be satisfied for pipeline acceptance. Some more details of petroleum courses in Islamabad  are as under.

The formation of free water with pressure and/or temperature reduction can result in the formation of hydrates if the temperature falls below the hydrate-forming temperature. This phenomenon is discussed more fully in the preceding section. In addition to the problems of hydrates, the formation of free water because of condensation can add to the horsepower requirements for pipelines because of increased pressure drops caused when water collects in low spots in the line and reduces the flow area of the gas. This condition is also conducive to corrosion in the pipe. Water vapors must be removed from the gas, and various methods used for this removal are discussed in the following.

Sour gas is the name commonly given to natural gas containing HIS. This HIS is found in concentrations varying from a trace on up to 30 mol% . The presence of H 1 S causes severe corrosion to occur when free water is present in natural-gas pipelines. When burned it forms sulfur dioxide, which is very toxic and can be a serious problem on the marketing end of the pipeline. Various methods for removal of H2S are discussed in the following. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.

Hydrocarbon Stabilization

The previous discussion covers the processes by which a maximum removal of liquefiable hydrocarbons from the gaseous phase of the well stream is accomplished to satisfy gas pipeline specifications and derive additional revenue from the liquid hydrocarbons. Technical Data used in the field explained in petroleum courses in Islamabad.  Unless the liquid hydrocarbons are handled properly after separation from the main gas stream, the maximum revenue will not be derived. The maximum is obtained by retaining the maximum volume of separated hydrocarbon liquids in atmospheric  storage and salvaging or recovering the maximum amount of light vapors that flash from the separated liquids.

If a liquid is to be stored at atmospheric pressure without vaporization losses, it must have a vapor pressure no greater than the existing atmospheric pressure at the maximum temperature it will reach in the storage tank. The vapor pressure exerted by the liquid is called its “true vapor pressure.” Measuring the true vapor pressure of a liquid is difficult. For this reason a standard vapor pressure, called the “Reid vapor pressure” (RVP) is much more frequently determined for the liquid. The RVP is determined by using a standard ASTM technique in a 100°F controlled-temperature bath. By sampling the liquid hydrocarbon product, the actual RVP of the liquid being produced can be determined. Some more details of petroleum courses in Islamabad are as under.

A correlation for approximating the true vapor pressure of a liquid for which the RVP has been determined. Because vapor pressure is composition dependent Fig. 14.14 should be considered an approximation only. If the maximum storage temperature were expected to be 6O”F, Fig. 14.14 shows that approximately a 29-psi RVP product could be stored. If the maximum storage temperature were , the maximum RVP for the product would be approximately 14 psi.

When the hydrocarbon liquids are dumped from the high-pressure separator, the liquids are at their boiling point for the pressures involved. Each reduction in pressure causes some vapors to be boiled off. If the liquids were dumped directly to a storage tank, violent boiling would take place, resulting in a loss of not only the lighter vapors but also some of the heavier ends. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.

Selective Adsorption Systems

On lean well streams where economic justification and payout of the equipment necessary for hydrocarbon removal by refrigeration are not possible, a selective adsorption system should be considered. This type of system frequently will be competitive in hydrocarbon recovery with mechanical refrigeration for lean gas streams. Technical Data used in the field explained in petroleum courses in Islamabad.

The selective adsorption system consists basically of two or more adsorption towers filled with a solid material capable of adsorbing hydrocarbons. The towers are controlled on a time cycle to be adsorbing, regenerating, and/or cooling. Alternatively, the bed is used to adsorb the desired quantity of hydrocarbon from the gas stream.

When the bed becomes saturated with hydrocarbons, the gas stream is switched to another bed. The saturated bed then is regenerated by passing hot gas through the bed. The hot gas vaporizes and drives off the adsorbed hydrocarbons. During the regeneration cycle, the bed and some of the parts of the adsorbed become heated and must be cooled before the bed can again be used on an adsorbing cycle. Some more details of petroleum courses in Islamabad are as under.

The approach used in hydrocarbon adsorption is the same as is widely used in dry-desiccant dehydrators. The basic difference is in the time allowed for the adsorption cycle. Dehydrators normally operate on a 6-hour or longer cycle. Hydrocarbon recovery units operate on a  much shorter time cycle and for this reason are frequently called  “short-” or “quick-cycle” units.

The non hydrocarbons present in the natural gas will have some effect on the process. This is especially true of the water vapors that eventually replace the hydrocarbons adsorbed in the bed and allow them to be expelled. The short-cycle unit is an excellent dehydrator as well as a hydrocarbon-removal unit. Presence of Hz S has little effect on the process unless oxygen is present. In this event, the oxygen causes free sulfur to form which will tend to foul the desiccant. CO;!, nitrogen, and other gases occasionally found in natural gas do not affect the process significantly. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Rawalpindi.