Often the oil contains natural gas. It is dissolved in the
oil because of the high pressure deep underground.
When the drill penetrates the oil-bearing layer this
pressure is released. It provides a tremendous thrust
and may be sufficient to bring all the oil to the surface.
If the gas pressure is not sufficient a pumping station
must be built to bring up the oil. This increases the
cost of the drilling operation. In its natural 'crude' state
oil consists of a mixture of various substances called
hydrocarbons. These substances must be separated
according to their densities, and purified. This process
is called refining.
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Feb 17, 18 05:06 AM
Printable and online grammar exercises-- How Much vs How Many worksheets with answers
Feb 17, 18 04:29 AM
Unless means except if. We use unless to make an exception to something we say. See details with examples and exercises.
Feb 16, 18 07:50 AM
Second conditional (type two) grammar exercise with answers -- Check your answers at the bottom of the worksheet.
Feb 14, 18 09:57 AM
If conditional type 1 (first conditional) grammar exercise with answers-- Check your answers at the bottom of the worksheet.
Feb 14, 18 03:36 AM
Uses of In Case, detailed rules explanations with examples and exercises for English learners and teachers
Feb 14, 18 03:32 AM
Uses of Wish Clauses, grammar rules with examples, exercises, and detailed explanations.
Feb 14, 18 03:26 AM
IF clauses / First, Second and Third Conditionals (Type 1, type 2, type 3) categories explained with details, examples and exercises
Feb 14, 18 03:22 AM
Third conditional if is used for unreal situations in the past. Type three conditional grammar, with examples and exercises
Feb 14, 18 03:21 AM
Second conditional IF also referred as Type 2 conditional is used for...See second conditional rules, examples and exercises
Feb 14, 18 03:19 AM
First conditional if (Type one conditional) is when the condition is in present or future... see details with examples and exercises