Offshore Drilling

The Introduction brought us quickly from the very early days of the oil industry to today’s jack up drilling units, semisubmersibles, and drill ships. Technical Data used in the field explained in petroleum courses in Islamabad.   This section will discuss the planning, preparation, and equipment necessary to conduct a typical floating drilling operation . Focus will be primarily on floating drilling because operations from jackups, submersibles, and platforms generally follow land drilling practices. The last portion of the section will be devoted to special considerations, such as deep water and high-current drilling and considerations  for cold and hostile environmental conditions. For a general discussion of the technology of offshore drilling, completion, and production.

The culmination of the sometimes arduous and complex task of geologic evaluation of a potential offshore play is for the exploration geologist to put a finger on the map and say “drill here.” This decision sets in motion a series of actions that will eventually lead to the drilling of an offshore well.

The first major step is to select a rig to drill the well. Because all rigs have specific operating criteria and limits, however, certain data must be known about the drillsite and surrounding area. Basic rig selection criteria consist  of water depth, expected environmental conditions during the forecasted drilling period (wind, waves, current profile, and climatological conditions), distance from nearest dock facility, and availability of consumable supplies (such as drilling mud, cement, pipe, rental tools, and spare parts). Some more details of petroleum courses in islamabad are as under.

Water Depth. A rough idea of the water depth is an important criterion for rig selection. If the water depth does not exceed approximately 350 ft, any of the three ma.jor rig types can be considered. Jackups can handle a water depth range from their shallow draft limit of 20 to 30 ft to a maximum depth of 350 ft. The maximum depth limitation is a function of other environmental constraints, such as wind, wave, and current conditions at the site. Severe conditions tend to lower the jackup rig’s maximum water-depth capacity. 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.

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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.

Removal of Water Vapor

In the preceding sections the removal of liquefiable hydrocarbons is discussed. The basic processes used for this removal of hydrocarbons invariably result in the removal of water vapors. Technical Data used in the field explained in petroleum courses in Islamabad. Experience has shown that the water-vapor dew point of the gas leaving the low temperature separator in these processes is from 10 to 12°F below LTS temperature for systems not using hydrate inhibitors and from 20 to 40°F below LTS temperature for systems using hydrate inhibitors.

Dew point depressions for selective adsorption systems will be discussed further, and the use of liquid desiccants will be covered for the field of gas dehydration in this section. To understand water-vapor dew point and dew point depression better, As was explained, this curve shows the saturation conditions for water vapor in natural gas. The water dewpoint temperature is the same as the saturation temperature for a given pressure. Assume that gas is flowing into a dehydration unit at 1,000 psia and 100°F and that it must be dehy drated to 7 lbm water/MMscf gas to meet contract specifications. At 1,000 psia and 100°F the gas contains 62 Ibm of water. The inlet water-vapor dewpoint temperature is 100°F. From the chart for 1,000 psia and 7 lbm water/MMscf the outlet water-vapor dewpoint temperature is 33°F. The dehydrator must be capable of producing a 67°F dew point depression and removing 55 lbm water /MMscf gas. Some more details of petroleum courses in Islamabad are as under.

Condensate is fractionated by the same process used in the system described. The light components pass overhead as vapor, and the stable product is withdrawn from the bottom of the tower. The bottom product is cooled in a heat exchanger either by the cold gas from the low-temperature separator or by cooling water. Overhead gas may be used for fuel and supply gas. If the volume warrants, it may be recompressed for sales gas. Heat is supplied with an indirectly fired salt-bath heater. 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.