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that may not have been flushed. They receive information indirectly from remnants of
the fluid that remain in pores of rock cuttings, as stains on the grain surface, or in
solution in the drilling fluid.
Oil may be identified as a sheen on the surface of water-based drilling fluid. If
the circulating fluid density is sufficiently low as to render an underbalanced drilling
condition, oil may be produced in large enough quantities that a sample may be
skimmed off a whole mud sample. Similarly, the underbalanced penetration of a gas-
bearing formation yielding only a small quantity of free gas in the mud system at the
bit will expand according to the real gas law as it is circulated to the surface, where it
may be detected and possibly sampled (although, in an uncontrolled situation, this
results in hazardous safety and environmental conditions). These are all fairly
obvious, direct indicators.

Speaking section

3. Make up a dialogue on the following situation and talk to your friend. Let
one of your group mates translate the dialogue consecutively.

You are visiting a drilling rig. Ask your guide to give you general information about
formation evaluation.

Grammar section

Impersonal Sentences
In impersonal sentences it is a formal subject, i.e. it does not represent any person or
things. This subject performs a purely grammatical function.
We use impersonal sentences in following cases:
a) To denote natural phenomena (such as state of weather, etc.) or that which
characterizes the environment. In such sentences the predicate is either a
simple one, expressed by a verb denoting the state of the weather, or a
compound nominal one, with an adjective as predicative.
It often rains in autumn.

It is cold in winter.
It is stuffy in here.
Note: the state of the weather can also be expressed by sentences in which the subject
denoting the state of things is introduced by the construction there + be. In such
sentences the noun introduced by the construction there + be is the subject:
There was a heavy frost last night.
We use impersonal sentences in the following cases:
b) To denote time and distance
It is five minutes past six.
It is morning already.
It is a long way to the station.
Note: Sentences with the impersonal it as a subject very often correspond to

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