Oil Underground Storage

Underground storage* is most advantageous when large volumes are to be stored. underground storage is especially advantageous for high-vapor-pressure products. Technical Data used in the field explained in petroleum courses in Islamabad. Solution-mined and conventionally mined caverns are not typically used for underground storage of refrigerated products. Underground storage allows most of the surface area (except for the entry wells) to be used for other purposes. This is especially beneficial in high-value, congested areas.

Types of underground storage are  caverns constructed in salt by solution Ming or conventional mining,  caverns constructed in nonporous rock by conventional mining,  caverns developed by conversion of depleted coal. limestone, or salt mines to storage, and  depleted reservoirs.

The solution-mined cavern is constructed by drilling a well or wells into the salt and circulating low-salinity water over the salt interval to dissolve the salt. a typical solution-mined cavern. Some more details of petroleum courses in islamabad are as under.

Conventionally mined caverns can be constructed any place a nonporous rock is available at adequate depth to withstand product pressures. An engineer or geologist experienced in underground storage should evaluate any specific site for the feasibility of constructing  underground storage. Most product caverns are constructed in shale, limestone, dolomite, or granite. This type cavern is operated “dry” (the product is recovered by pumping).

The cavern may be operated by brine displacement of product or pump-out methods Most solution-mined caverns are operated by the brine displacement technique (Fig. 1 I .9). A suspended displacement string of casing is installed near the bottom of the cavern. and product is injected into the annulus between  the product casing (casing cemented at cavern roof) and the displacement casing, forcing brine up the displace ment casing. The procedure is reversed for product recovery. In this type operation, a brine storage reservoir usually is provided.

Some solution-mined caverns are operated “dry” by installing a pump at cavern depth either within the cavern or in a well connected to the cavern by fracturing. Both submersible electrically driven pumps and deep-well vertical multistage pumps are used for this purpose. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Rawalpindi.

Vapor-Recovery System

Vapor-recovery systems are of two basic types. One type connects a vacuum line to the tank and transports the tank vapors to a processing or gasoline plant. Technical Data used in the field explained in petroleum courses in Rawalpindi. The other type consists of a small compressor located by the tank battery. which compresses the tank vapors to a pressure suitable for lease use or sales.

Vacuum-Line System. The vacuum-line system usually is found only in large oil fields, where many tank batteries can be connected together into a relatively short gathering system. This system must employ well-maintained and properly functioning pressure/vacuum relieving devices and dependable control valves to prevent the tanks from collapsing or air from entering the gathering system. Some more details of petroleum courses in rawalpindi are as under.

Compression System. The compressor system is usually electrically driven and all components are skid mounted Some of these systems use a vane-type compressor and inject a refined oil by way of a lubrication system to seal the vanes against the compressor walls. In these systems an actual liquid recovery is accomplished by the sealing oil absorbing the condensed hydrocarbons from the compressed vapors and transporting them to storage with the returning sealing oil. Applications for this type of system are twofold: (I) compression of the rich stocktank  vapors for sale to a gasoline plant and (2) the recovery of liquids from the rich stock-tank vapors. Liquid hydrocarbons also can be recovered from the compressed vapor-recovery unit (VRU) vapor by either one or both of the following means.

A vapor cooling system (air-cooled or water-cooled) heat exchanger can be installed complete with a separator downstream of the hot compressed VRU vapor stream. Multiple vapor cooling systems may he used in between the stages of a multiple-staged compressron system. 2. A mechanical refrigeration unit may be installed downstream of the VRU for a higher-yield liquid hydrocarbon recovery. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join oil field after petroleum courses in Islamabad.

Preventing Evaporation and Gravity Losses

Much can be done by the producer to prevent undue losses of crude oil by evaporation. Products should be introduced into storage as cool as possible and kept that way. Technical Data used in the field explained in petroleum courses in Rawalpindi. Some types of heat-exchange equipment should be employed between an emulsion treated, or other heating equipment, and the tanks to cool the oil before it enters storage. If fluid heat exchangers are used, a preventive maintenance program should be employed to guard against buildup of scale. paraffin. salt. etc.. which are common to many pro diced fluids. Most modern tank batteries are equipped with lease automatic custody-transfer (LACT) units. The  run tank should be of sufficient size to allow approximately I2 hours’ settling time. Where batteries are equipped with storage for bad oil. this storage should be kept to a minimum and the battery treating capacity should be capable of treating a certain amount of bad oil. Some more details of petroleum courses in rawalpindi are as under.

Steel tanks should be painted with a reflective or white paint. Tests show the vapor-space temperature of a tank painted with aluminum paint to average 4%“F above atmospheric temperature. while a red-painted tank averaged 14°F above atmospheric temperature. Tanks should be selected with smaller diameters. Greater heights. and smaller capacities, all other considerations being equal. These factors will allow the stored product to have relatively smaller surface areas and vapor spaces as well as a shorter length of storage time before being sold.

Down comer pipes prevent undue agitation in the tank. They are usually made by installing a line inside the tank from the inlet connection in the tank deck to 1 ft above the tank bottom. The down comer must have a vacuum breaker hole at the top to allow gas to escape and thereby prevent agitation, splashing, and accumulation of static electricity. All tank openings should be maintained closed and pressure on the tank should be as high as practical (at least r/z in. of water column). Tanks in a battery all should be connected together into a common vent line to keep breathing and filling losses to a minimum. Bypass thief hatches are manufactured that will do much to prevent evaporation losses when a tank is gauged through the thief hatch. These special hatches have the tank-battery vent lines connected to them and will close off or isolate all other tanks except the one being gauged. This allows all other tanks in the battery to maintain their pressure while the tank being gauged is depressed The producer may install one of several types of ground level gauging and sampling devices available that will permit gauging and sampling without opening the tank. The tank remaining closed goes far toward eliminating evaporation losses. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.

Factors Contributing to Vapor and Gravity Losses

Several factors affect and contribute to vapor and gravity losses in storage tanks: (I) vapor pressure of the product stored, (2) temperature of the product stored. (3) surface area of the product stored. Technical Data used in the field explained in petroleum courses in Rawalpindi.  (4) agitation of the product stored, (5) pressure on the storage tanks, (6) filling losses from the storage tanks, (7) breathing losses from the storage tanks, (8) size of the storage tanks, and (9) color of outside paint or coating. Several, if not all, of these factors usually contribute to the total loss from any one tank or battery.

The true vapor pressure (TVP) of a liquid is the actual pressure it exerts on the vapor space in a container at a given temperature. Water, for example, has a TVP of 1 psi at 100°F and a TVP of 14.7 psi at 212”F, yet it must be kept in a closed container to prevent evaporation. The same is true for crude oil if the TVP is below 14.7 psi. Crudes with a TVP of 10 psi and lower are usually relatively stable in closed-atmospheric storage. Some more details of petroleum courses in Rawalpindi are as under.

Temperature of crude is directly related to its vapor pressure. For example, a crude with a TVP of 8 psi at 50°F will have a TVP of 17 psi at 90°F. The vaporization loss is then approximately doubled at the90°F temperature.

Directly related to the rate of evaporation is the surface area of the crude. Take, for example, two tanks with a capacity of 500 bbl each, one a high 500-bbl tank and the other a low .500-bbl tank. If both are filled one-half full, the high 500 bbl has 0.74 sq ft of surface area exposed per  barrel stored, whereas the low 500 bblhas 1.46 sq ft of surface area exposed per barrel stored. The low SOO-bbl tank then has twice the evaporation rate of the high 500-bbl tank. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.

Factors Contributing to Vapor and Gravity Losses

Several factors affect and contribute to vapor and gravity losses in storage tanks: (I) vapor pressure of the product stored, (2) temperature of the product stored. (3) surface area of the product stored. Technical Data used in the field explained in petroleum courses in Rawalpindi. (4) agitation of the product stored, (5) pressure on the storage tanks, (6) filling losses  from the storage tanks, (7) breathing losses from the storage tanks, (8) size of the storage tanks, and (9) color of outside paint or coating. Several, if not all, of these factors usually contribute to the total loss from any one tank or battery.

The true vapor pressure (TVP) of a liquid is the actual pressure it exerts on the vapor space in a container at a given temperature. Water, for example, has a TVP of 1 psi at 100° F and a TVP of 14.7 psi at 212”F, yet it must be kept in a closed container to prevent evaporation. The same is true for crude oil if the TVP is below 14.7 psi. Crudes with a TVP of 10 psi and lower are usually relatively stable in closed-atmospheric storage. Some more details of petroleum courses in rawalpindi are as under.

Temperature of crude is directly related to its vapor pressure. For example, a crude with a TVP of 8 psi at 50°F will have a TVP of 17 psi at 90°F. The vaporization loss is then approximately doubled at the 90°F temperature.

Surface Area. Directly related to the rate of evaporation is the surface area of the crude. Take, for  example, two tanks with a capacity of 500 bbl each, one a high 500-bbl  tank and the other a low .500-bbl tank. If both are filled one-half full, the high 500 bbl has 0.74 sq ft of surface area exposed per barrel stored, whereas the low 500 bbl has 1.46 sq ft of surface area exposed per barrel stored. The low SOO-bbl tank then has twice the evaporation rate of the high 500-bbl tank. TSK Training for Skills and Knowledge is the best institute in Rawalpindi Islamabad for Pakistani Students who wants to join petroleum courses in Islamabad.