Page 97 - Drilling Technology in Nontechnical Language

88 Drilling Technology in Nontechnical Language Second Edition

Fig. 4–3. Sand control screen, cut away to show screen elements

If the well gets too close to the oil-water interface, the water (being less
viscous than the oil) will “break through” the oil and flow to the well. This

is called coning (fig. 4–4). Once coning starts, the well will produce water
and not too much oil. Similarly, if the well gets too close to the gas, the
gas will be preferentially produced. In a vertical well, there is only a short
interval of the well that can be perforated to produce the oil. This means

that to produce a reasonable amount of oil, the speed that oil has to flow
towards those few perforations is high, which will tend to draw gas from
above or water from below towards the well.

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