Applied Biostratigraphy

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==== Production ====
Biostratigraphy is an invaluable part of modern production drilling and it is likely that significant dollar value can be attributed to its use. In fact, biostratigraphy can be utilised in “real-time” operational drilling situations during exploration, appraisal and production phases. The general operational aspect of biostratigraphy is discussed later in this manual.

Maximising production from a field requires the optimum placement of production wells both laterally and vertically within a reservoir. The advent of horizontal production wells has shown to clearly demonstrate a significant advantage when compared with more conventional, vertical or subvertical wells.

It is estimated that operational biostratigraphy in the North Sea alone adds around £2 billion of economic value each year to oil & gas revenues (Haydon Bailey, Network Stratigraphic Consulting Ltd. pers. comm.).

Techniques revolve mainly around placing the production well bore along optimum trajectories (“biosteering”) and in the accurate placement of casing strings to mitigate against pressure differentials (“geostopping”).

**Biosteering**

Biosteering is discussed in further detail later, suffice to say here that biostratigraphy allows relatively complex borehole trajectories to be drilled and unconventional reservoirs (in terms of structure and geometry) exploited.

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//Schematic trajectory of a typical "horizontal" production well. Biozones (coloured blocks) are shown on the left
(diagram from StrataData Ltd.).//


**Geostopping**

Geostopping is the identification of specific biozonal horizons at which drilling needs to stop in order to effect an operational/engineering change (Figure 7). This will be discussed further below.

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//“The Driller’s Intimate Friend” - a hand-drawn poetic homage written in the early part of the 20th century to a species of foram – “Miliola B” which, when observed in drilled samples from the Middle East, indicates entry into economic basement and therefore the signal that drilling can cease on a well and the rig prepared for the next job. This shows that wellsite biostratigraphy in some form has been around for quite a while in the oil industry!//