Page 18 - Drilling Technology in Nontechnical Language

Chapter 1 – DRILLING GEOLOGY 9

need a good understanding of shale chemistry and physical attributes in
order to drill wells to economically reach their objectives.

Sandstones

A sandstone structure consists of particles of sand (mostly quartz
grains, often colored by the presence of traces of other minerals, such as
iron). The sand grains are pressed together by the weight of the sediments

deposited above (fig. 1–7). In the spaces between the grains was originally
water, which may contain all sorts of dissolved minerals and salts. Over
time, materials may come out of solution and be deposited where the grains
come into contact with each other. This cementation might be strong or
weak, depending on the minerals involved and on how much is deposited.
With weak cementation, the sandstone may start to fall to pieces when

drilled through. If it is a reservoir rock, the flow of hydrocarbons from
the formation into the producing well may bring sand with it, which can
damage or block production equipment if the well is not designed to
prevent it.

Fig. 1–7. Sandstone structure

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