Fundamentals of Petroleum Engineering (Practical)By: Bilal Shams Memon

Object: To determine the viscosity of crude petroleum & petroleum products on SuS/SuF by Saybolt Viscometer.

Apparatus: Saybolt Viscometer, crude oil, stop watch.

Theory: The efflux time in seconds of 60ml of sample flowing through calibrated orifice factor & reported as viscosity of sample at that temperature.

Procedure: Following steps are followed in this experiment.

1. In the test, temperature is above the room temperature. Test may be expedited by preheating sample not more than 3 F above the test temperature.⁰

2. Insert a cork stopper having a card attached for its easily removed into the air chamber at bottom of viscometer. The cork shall be fit tightly enough to prevent escape of the air evidenced by the absence of oil on the cork when drawn.

3. Filter the prepared sample through 100 mesh screen directly in the viscometer until the level is above the gee flow rim.

4. Stir the sample as its temperature will remain constant within 0.05 F of the test ⁰temperature during 1 min of continuous stirring. Stir with a viscometer thermometer equipped with viscometer support. Use circular motion at 30 to 50 rpm in horizontal plain.

5. Remove thermometer from the sample quickly, also remove the oil from the gallery until its level reaches blow the overflow rim of flask. This is done by placing the tip of withdrawal tube at one point in the flow rim withdrawal tube.

6. Place the receiving flask where steam of oil from bottom of viscometer will just strike the neck of flask. The graduated mark on the flask shall be between 10 to 13 cm from the bottom of viscometer.

7. Snap the cork from the viscometer using attached cork. At the same instant, start the time in stopwatch. Stop the timer at the instant when oil in bottom of the flask reaches the graduation mark. Now record the efflux time in seconds.

Results:37(SuS) at 37.7 C temperature⁰

Efflux time is 2.89 Sec / 60 ml.

Object: To determine the specific gravity of crude oil by hydrometer.

Apparatus: Measuring cylinder, hydrometer, water & crude oil.

Theory: The sample is brought to prescribed temperature & transformed to the cylinder at approximately same temperature. The appropriate hydrometer is lowered into sample & allowed to settle. After the temperature equilibrium is reached, the hydrometer displays the specific gravity of crude oil.

Procedure: Following steps are followed in this experiment.1. Transfer the sample of crude oil to a clean hydrometer

cylinder without splashing to avoid formation of air bubble. Remove if any air bubble formed.

2. Place the cylinder containing the sample in vertical position in a location free from air bubbles. Ensure that temperature of sample does not change.

3. Lower the hydrometer gently into the sample. Take care to avoid wetting the stamp above the level to which it will be merged in the liquid.

4. When hydrometer has come into rest, even floating freely away from the walls of the cylinder, estimate the hydrometer scale reading. The correct reading point on hydrometer scale is at which the principle surface of liquid cuts the scale.

Result: Measured specific gravity of sample of crude oil is 0.789.

Object: To determine the presence of salt in crude oil. Apparatus: Salt analyzer, pipette (10ml), beaker (100ml),

measuring cylinder. Given materials: Paraffin oil, sample (crude oil), mixed alcohol

(methanol + butanol) Procedure: Following steps are followed in this experiment.

1. Accurately measure the 100ml sample & pour it into 100ml measuring cylinder.

2. Add 40 ml xylene & mix it well.3. Add some of the mixed alcohol & stir it hard. Now pour it into

measuring beaker & stir it with electrode.4. Switch on the analyzer & set the pointer at 100 µA with scale

adjustment. Then read the position.

5. Select low position if there is no change occurs in scale.

6. Select medium position if there is no changing in scale.

7. Select high position if there is no changing in reading.if no change displayed on any scale, it means there is absence of salt in crude oil.

Result: The salt is present in crude oil as the

changed displayed on low position scale.

Object: To discuss the classification of crude oil & natural gas.

Crude oil: It is defined as a naturally occurring complex mixture of hydrocarbons. It has two types:

1. Heavy crude oil. 2. Light crude oil.Heavy crude oil: Viscous & non-produce-

able oil, can’t flow easily.Light crude oil: light & produce-able oil that

flows easily.

There are 3 principle hydrocarbon series.1. Paraffin 2. cyclic paraffin 3. aromatic.Paraffin: Chemically stable compounds, have either

straight or branched chain structure. These crude oil contains paraffin, having more volatile constituent (due to having low boiling point). They have general formula: CnH2n.

Cyclic paraffin: They have general formula CnH2n. They have ring structure like cyclo-propane, cyclo-butane.

Aromatic: they have general formula CnH2n-6. They are chemically active & contains benzene ring.

Classification on basis of base:Paraffin base: Its chief components are paraffin, which when

completely distilled leaves a solid residue of wax.Asphalt base: Primarily composed of cyclic compounds, which

when completely distilled leaves solid residue of asphalt.Mixed base: An oil having properties of both bases. Quality of crude oil: Crude oil’s quality depends mainly on

API gravity which measures the oil density. The price which a producer receives depends on oil gravity; less dense oil that contains more valuable products like gasoline (having high API gravity) becomes more valuable.

Formula: API gravity = (141.5 / specific gravity) – 131.5

Natural gas: Unique mixture of hydrocarbons, primarily composed of light members of paraffin series & has methane as a dominant component. It has also impurities like CO2, H2S, H2O (vapors), N & He.There are following basic classification of natural gas.

Wet gas: Gas contains an amount of natural gasoline & water vapors.

Sweet gas: Gas contains no H2S.Sour gas: Gas containing H2S.Dry gas: Gas free from natural gasoline & water

vapors

Chemical composition: Natural gas is mainly considered to having light paraffin from C1 – C4, S, N, O. They are generally present in following percentage: Elements Percentage

C 65-80%

H 19-25%

S 0-0.2%

N 1-1.5%

O 0% or negligible

Natural gas generally have following percentage of paraffin series:

Compounds Percentage

CH4 60-94%

C2H6 1.05%

C3H8 0.28%

C4H10 0.17%

N2 3.88%

CO2 0.72%

Object:To demonstrate the function of Christmas-tree & its components.

Theory: A Christmas tree is an assembly of valves, flanges & connections that control the flow of fluid from the well.Many types of christmas tree are available (like pumping wells christmas tree & consist of mainly stuffing box. These complex trees with numerous master & wing valves are also installed on deep high pressure gas wells. Each well is unique & requires specific type of tree.For high rate well, the flow of tree is often “Y” shaped just to reduce turbulence & erosion. Similarly flow control valve is installed in a straight run rather than conventional right angle beam arrangement; a second side (wing) out valve. This is often used in high pressure well kill connection for a tubing kill line.The main valve of christmas tree is master valve which is attached above the tubing head & on master valve that is used to shut off the production & is important for well service & workover.

Component of tree: In-spite of wide variety of tubes available, they shares certain basic components:

i. Pressure gauge – It monitors tubing & casing-annulus pressures.

ii. Gauge flange – It seals the cap of tree & has fitting for pressure gauge. When gauge hanger is removed, the tubing becomes accessible & bottom hole testing equipments can be installed.

iii. Crown on swab valve – It shuts off the well from wire-line coil. Tubing on other work-over unit is to be riches up.

iv. Flow on croupy – Flow tree allows to be run into the well during well production

v. Wing valve – It shut in the must routine operation. This valve is the earliest valve that replaced on the tree.

vi. Choke – It is used to control the amount of flow rate either it will be fixed choke or adjustable.

vii. Master valve – This valve is used to shut off the well.

viii. Tubing head – It is flange steel fitting body with gauge that is of packed mechanism having tubing hanger (part of valve). Tubing head seals annular space between tubing & casing while suspending the tubing string in the valve. Also it provides the connection that supports the christmas tree.

ix. Christmas tree – It is a heavy flanged steel fitting connected to the first string of casing. It provides slips for casing & packing assemblies, allows suspension of intermediate & production string of casing.

Object: To demonstrate the function of well head & its components.

Theory: The collective assembly of valves & connections at the top of well is known as well head.This equipment’s primary purpose is to control pressures of flowing fluid. Well head equipments supports tubular, provide seal & control the path & flow rate of fluid. All well head includes at-least one casing & tubing heads & hangers & one christmas tree.

Function of well head & its components:Major components of well head are:

Casing head: It is screamed or welded to outer most casing stub. Its inside provides a shouldered sealing surface for casing hanger which grips the casing, usually allows the weight of casing string to provide necessary force to seal the annulus between outer tubing & inner casing string (to be hung & sealed off above the casing head) or spot in mined with temporary bushing to prevent damage from drill pipe rotation.

Tubing head: It accommodate the tubing hanger which usually screw on top of tubing string & seal off casing tubing space by rubber sealing elements. Tubing hanger further screamed by screws, an adopter (tubing bonnet) provides tension from tubing head to well arrangements & fittings above the casing & tubing head that are used to control flow.

Christmas tree: In christmas tree, bottom valves are master valves. Its primary function is to completely shut in the well.

Object:To demonstrate the function of choke. Theory: In oil field terminology, choke was

adopted to designate flow & regulate an oil or gas well to the required amount of production.

Types of choke: There are three types generally:1. Positive 2. Adjustable 3.

Rotary.1. Positive choke – This is an orifice usually

elongated of a chosen size that changes the flow rate. Orifice are half to six inches bored. These chokes were originally merely of solid pipe nipples with holes through them. They are now mostly replaceable orifice with thread & seal.

2. Adjustable choke – This is long pointed tube needle valve with same type modified venture orifice seat. By turning a calibrated land wheel, the choke capacity may be set to an approximation of an equivalent positive choke.The micrometer indicator on stem moves along the scale attached that opens other variation of pointer; indicators are also used. The locking cap provides quick removal of stem whilst choke’s seat is similar to positive choke beam which is trapped carefully at inlet to match the stem tap & orifice is their modified venture. Adjustable choke is not used as valve for completely closing purpose. The pressure required for closure may deform the seat & stem destroy their accuracy.

3. Rotary choke – This choke contains a rotating interior sealed disc that carries six positive choke bean. Disc can be turning by inserting a bar in rotating shaft. Advantage of this type of choke is that it can be installed or changed outside at atmospheric pressure, which make inspection easy & well does not have to be closed in.