|
Offshore fields
The simple model for an offshore basin may comprise a
series of fields discovered over a lengthy period. Assuming no
disruptions to development, it can be assumed that fields come into
production within 3 or 4 years of their discovery. They peak rapidly and
then begin to decline at an increasing rate until a steady decline rate
is established.
A typical profile is shown in the figure below which
matches the sort of profile that may be found in many of the offshore areas that
began development in the 1970s. Later deep water profiles appear to be
developing a steeper profile in the upward and downward curves as
improved technologies promote faster depletion. Look at
Norway and
Angola as examples.
Onshore fields
The simplified
onshore profile is similar to the offshore profile although growth in output
tends to be slower for individual fields (as wells are tied in as they are
drilled rather than all at once) and their decline rates are reduced (as
cheaper infill wells can be used to sustain production volumes). The
profile shown below is typical for onshore basins developed through
the 19th Century, although again new technology is now increasing the
gradient of both the up and down slopes. Look at and
Ecuador and
Yemen as examples.
Conclusions
Such models
can be used to forecast profiles for producing basins as well as defining brand new basins, and potential yet-to-find
volumes in immature and mature basins. In truth each represents a single
play in a basin but empirical observation of existing profiles that are
already past their peak show that models can be a fair approximation of
what happens in reality.
However it is
important to note that many other factors, in addition to geology and
engineering, such
as politics, economics and natural events, serve to disrupt the smooth
nature of growth and decline, especially for onshore fields. The OPEC
country profiles - for example those of
Iran and Venezuela -
have seen dual peaks before and after restrictions
were in place through the mid 1980s to the end of the 1990s. Other
countries with economic disruption - for example
Russia in the 1990s - bear little relationship
to modelled profiles.
In
analysing future output special circumstances of the past, and potential
special circumstances of the future, must always be taken into account.
© 2007 Dr Michael R.
Smith
(all quotes from this article should be
cited: "Dr Michael R.
Smith, Chief Executive of Energyfiles, the oil and gas forecasting
company")
|
MODELS DESCRIBING PRODUCTION PROFILES MAY
BE SIMPLIFIED BUT FULL ANALYSES REQUIRE MORE THAN JUST MATHEMATICS