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API GRAVITY

The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

API gravity is thus an inverse measure of a petroleum liquid's density relative to that of water (also known as specific gravity). It is used to compare densities of petroleum liquids. For example, if one petroleum liquid is less dense than another, it has a greater API gravity. Although mathematically, API gravity is a dimensionless quantity, see the formula below, it is referred to as being in 'degrees'. API gravity is graduated in degrees on a hydrometer instrument. API gravity values of most petroleum liquids fall between 10 and 70 degrees.

History of development

In 1916, the U.S. National Bureau of Standards accepted the Baumé scale, which had been developed in France in 1768, as the U.S. standard for measuring the specific gravity of liquids less dense than water. Investigation by the U.S. National Academy of Sciences found major errors in salinity and temperature controls that had caused serious variations in published values. Hydrometers in the U.S. had been manufactured and distributed widely with a modulus of 141.5 instead of the Baumé scale modulus of 140. The scale was so firmly established that, by 1921, the remedy implemented by the American Petroleum Institute was to create the API gravity scale, recognizing the scale that was actually being used.^[1]

API gravity formulas

The formula to calculate API gravity from Specific Gravity (SG) is:

${\displaystyle {\text{API gravity}}={\frac {141.5}{\text{SG}}}-131.5}$

Conversely, the specific gravity of petroleum liquids can be derived from their API gravity value as

${\displaystyle {\text{SG at}}~60^{\circ }{\text{F}}={\frac {141.5}{{\text{API gravity}}+131.5}}}$

Thus, a heavy oil with a specific gravity of 1.0 (i.e., with the same density as pure water at 60 °F) has an API gravity of:

${\displaystyle {\frac {141.5}{1.0}}-131.5=10.0^{\circ }{\text{API}}}$

Using API gravity to calculate barrels of crude oil per metric ton

In the oil industry, quantities of crude oil are often measured in metric tons. One can calculate the approximate number of barrels per metric ton for a given crude oil based on its API gravity:

${\displaystyle {\text{barrels of crude oil per metric ton}}={\frac {{\text{API gravity}}+131.5}{141.5\times 0.159}}}$

For example, a metric ton of West Texas Intermediate (39.6° API) has a volume of about 7.6 barrels.

Measurement of API gravity from its specific gravity

To derive the API gravity, the specific gravity (i.e., density relative to water) is first measured using either the hydrometer, detailed in ASTM D1298 or with the oscillating U-tubemethod detailed in ASTM D4052.

Density adjustments at different temperatures, corrections for soda-lime glass expansion and contraction and meniscus corrections for opaque oils are detailed in the Petroleum Measurement Tables, details of usage specified in ASTM D1250. The specific gravity is defined by the formula below.

${\displaystyle {\mbox{SG oil}}={\frac {\rho _{\text{crudeoil}}}{\rho _{{\text{H}}_{2}{\text{O}}}}}}$

With the formula presented in the previous section, the API gravity can be readily calculated. When converting oil density to specific gravity using the above definition, it is important to use the correct density of water, according to the standard conditions used when the measurement was made. The official density of water at 60 °F according to the 2008 edition of ASTM D1250 is 999.016 kg/m³.^[2] The 1980 value is 999.012 kg/m³.^[3] In some cases the standard conditions may be 15 °C (59 °F) and not 60 °F (15.56 °C), in which case a different value for the water density would be appropriate (see standard conditions for temperature and pressure).

Direct Measurement of API gravity (Hydrometer method)

There are advantages to field testing and on-board conversion of measured volumes to volume correction. This method is detailed in ASTM D287.

Classifications or grades

Generally speaking, oil with an API gravity between 40 and 45° commands the highest prices. Above 45°, the molecular chains become shorter and less valuable to refineries.^[4]

Crude oil is classified as light, medium, or heavy according to its measured API gravity.

• Light crude oil has an API gravity higher than 31.1° (i.e., less than 870 kg/m³)
• Medium oil has an API gravity between 22.3 and 31.1° (i.e., 870 to 920 kg/m³)
• Heavy crude oil has an API gravity below 22.3° (i.e., 920 to 1000 kg/m³)
• Extra heavy oil has an API gravity below 10.0° (i.e., greater than 1000 kg/m³)

However, not all parties use the same grading.^[5] The United States Geological Survey uses slightly different ranges.^[6]

Crude oil with API gravity less than 10° is referred to as extra heavy oil or bitumen. Bitumen derived from oil sands deposits in Alberta, Canada, has an API gravity of around 8°. It can be diluted with lighter hydrocarbons to produce diluted bitumen, which has an API gravity of less than 22.3°, or further "upgraded" to an API gravity of 31 to 33° as synthetic crude.^[7]

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Rig Derrick Load Calculation

...sebuah copy paste bulat bulat....

by DRILLINGFORMULAS.COM on SEPTEMBER 22, 2013

The drilling line is reeved over a set of crow block and down to another set of sheaves known as travelling block. The hook connected to travelling block is used to suspend the drilling load. One end of drilling line is wound onto the drawworks and this line is called “Fast Line”. Other end of the drilling line is tied into an anchor point on the rig floor and this line is named as “Dead Line”. The drilling line is reeved around the blocks several times in order to meet required load.

According to the diagram above, we can use basic physic to determine derrick load.

Static Derrick Load

 Load Analysis Using Free Body Diagram on Travelling Block Under Static Condition

W = N x Tf

Tf = W/N

Where,

W – Hook load

N – Number of drilling lines in a travelling block

Tf = Td (Tf and Td are the same value because the same tension in the drilling line)

Load Analysis Using Free Body Diagram on Derrick Under Static Condition

Static derrick load equates to summation of fast line tension, dead line tension and hook load. We can describe into the following equation.

FD = Tf + W + Td

Where,

FD – Static derrick load

Tf – Fast line tension

Td – dead line tension

W – hookload

Note: Neglect a small effect of small angle of the fast line and the dead line.

FD = W/N + W + W/N

FD = (N+2) x W ÷ N

 Dynamic Derrick Load

Under dynamic condition, friction in sheave bearings and block lines make the fast tension higher than the dead line tension. It means that the fast line tension will increase under a dynamic condition; however, the dead line tension will remain the same because it is still in static condition.

The fast line tension under the dynamic environments can be described as the equation below;

Tf = W ÷ ( E x N )

Where,

Tf – The fast line tension.

W – Block weight

N – Number of lines

E – Efficiency

Table#1 – Efficiency Factor for Wire Rope Reeving for Multiple Sheave Blocks (API RP9B)

Derrick load under dynamic condition is also equal to summation of hook load, dynamic fast line tension and dead line tension as described in the equation below

FD = Tf + W + Td

Exercise for Derrick Load Calculation

Buoyed weight of the drill string is 260,000 lb which will be pulled out of hole. Weight of travelling block and hook is 40,000 lb. The rig has 10 lines strung in crown block and travelling block.

Solution:

Efficiency of 10 lines = 0.811

Total hook load = 260,000 + 40,000 = 300,000 lb

The fast line tension:

Tt = 300,000 ÷ (10 x 0.811)

Tt = 36,991 lb

The dead line tension:

Td = 300,000 ÷ 10

Td = 30,000 lb

Derrick load under the dynamic condition:

FD = Tf + W + Td

FD = 36,991 + 30,000 + 300,000

FD = 366,991 lb

Derrick load in dynamic condition equates to 366,991 lb

Ref books: Drilling engineering books

SWL Wire Rope

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Mungkinkah manusia mengebor bumi sampai tembus?

Apakah manusia mengebor bumi sampai tembus?

Tentu saja tidak mudah menjawab pertanyaan itu. Sekarang, tampaknya mustahil manusia bisa mengebor bumi sampai tembus. Entah di masa-masa mendatang, barangkali manusia menemukan teknologi yang lebih maju di bidang pengeboran.

Yang jelas, bola bumi memiliki diameter sepanjang 12.756 kilometer atau lebih dari 12 juta meter. Jadi, kalau manusia ingin mengebor bumi sampai tembus, diperlukan alat bor yang panjangnya lebih dari 12 juta meter. Wow…, panjang sekali.

Selain itu, suhu di inti bumi sangat panas. Inti bumi terdiri dari nikel beku setebal 1.370 km dan suhu mencapai 4.000 0C. Wow, panas sekali, ya? Apa alat bornya tidak meleleh pada suhu setinggi itu?
Pengeboran Terdalam

bumi terdiri atas empat lapisan yang berbeda. Para ahli geologi menyatakan, sejak bumi mendingin 4,6 milyar tahun lalu, material yang berat “tenggelam”, sedangkan materi yang ringan muncul ke permukaan. Karenanya, lapisan kulit bumi terbuat terbuat dari materi yang ringan seperti batu granit. Sedangkan bagian dalam bumi berisi logam berat seperti nikel dan besi.



Kulit bumi adalah tempat yang kita tinggali ini. Di bawahnya adalah mantle (mantel), berupa materi berbentuk pasta seperti bubur. Inti bumi sangat panas dan memiliki tekanan yang sangat tinggi. Tubuh manusia akan hancur seperti perkedel jika datang ke pusat inti bumi karena tekanan yang sangat tinggi.

Manusia melakukan pengeboran bumi untuk beragam alasan. Untuk penelitian, mencari minyak, air, atau tujuan lain. Manusia sudah berhasil meneliti lapisan kulit bumi, tetapi inti bumi masih menjadi misteri.

Pengeboran minyak bumi biasanya ”tidak dalam”. Pada kedalaman 6.000 meter, minyak sudah ditemukan. Pengeboran terdalam yang pernah dilakukan manusia adalah yang dilakukan di Kola Peninsula, Rusia.

Pengeboran itu dimulai pada 1970 dan mencapai kedalaman 12.262 meter pada tahun 1994. Teknik pengeboran tidak dengan memutar alat bor, tetapi ditekan sedikit demi sedikit sambil mengeluarkan lumpur.


Tujuan pengeboran Kola Peninsula adalah 15 ribu meter. Tetapi tidak berhasil. Pada kedalaman itu, suhu mencapai bisa mencapai 300 derajat celcius atau bahkan lebih tinggi lagi. Terlalu panas untuk mengoperasikan alat bor di sana.

Pengeboran lain yang cukup dalam dilakukan di laut Kaspia. Mencapai kedalaman hampir sedalam di Kola Peninsula. Selain itu, ada pengeboran untuk riset di Bertha Rogers, Oklahoma, Texas dengan kedalaman 9.583 meter.

Pada pengeboran di Peninsula, tidak ditemukan minyak atau sumber alam. Tetapi ilmuwan berhasil mempelajari susunan lapisan bumi, termasuk lempeng yang berkaitan dengan gempa bumi serta komposisi fisik dan kimia dari inti bumi.

Tidak selamanya manusia melakukan pengeboran dari darat. Manusia juga melakukan pengeboran di laut. Bisa dengan menririkan pangkalan bor di laut, biasa disebut rig. Bisa juga mengebor melalui kapal, seperti kapal “Joides Resolution”. Kapal Joides Resolution memiliki tujuh lantai, milik Joint Oceanographic Institute yang bergerak di bidang penelitian ilmiah.

Nah, manusia telah mampu mengebor ke bumi sedalam lebih dari 12 ribu meter. Padahal diameter bumi mencapai 12 juta meter. Jadi, baru satu dibanding seribu. Mungkinkah suatu saat manusia bisa mengebor bumi sampai tembus?

Jawabannya Mungkin SAJA

Kita tidak tau apa yang terjadi pada masa yang akan datang,

Aku pernah mendengar bahwa teknologi sekarang hanyalah 28% nya dari teknologi masa depan..






sebuah copypaste dari http://www.huteri.com/

akumulstor