Page 43 - Drilling Technology in Nontechnical Language

34 Drilling Technology in Nontechnical Language Second Edition

Fig. 3–1. Part of the UK onshore licensing map

Small companies sometimes pay for a block, invest enough to identify
good prospects, and then look for larger companies to buy in as partners.

If this works, then the new partner will likely fund the first one or two
wells, “carrying” the small company, to become a partner on the block. In
this way, the small company can then increase its value many times with a
relatively small investment.
An exploration well is drilled to gain information. It is usually a
false economy to try to drill an exploration well to later produce oil. A
producing well cannot be properly designed until the reservoir is known
in sufficient detail (pressures, fluids and gases present, permeability, how

well consolidated the reservoir rock is, and many other factors). Many

things about the subsurface conditions cannot be predicted on the first
well. This means that the well design may have to change if unexpected
conditions are encountered while drilling. Exploration wells should be
minimum-cost wells designed to obtain essential information and be
abandoned afterwards.

Well Proposal

For this example well, an angular unconformity structure is present (as
was discussed in chapter 1), providing a potential trap for oil and gas. The
geologists believe that it will contain a gas cap on top, with a column of oil
and water below. It was decided to drill a well into the edge of the gas cap
and follow the bedding plane down through the oil and into the water, so

that several facts (the well objectives) could be established (fig. 3–2):

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