4
Equinor, Annual Report on Form 20-F 2021
When applicable, the volumetric method was used
to estimate the original oil in place (OOIP) and
original gas in place (OGIP).
Structure maps were prepared to delineate each
reservoir, and isopach maps were constructed to estimate reservoir volume.
Electrical logs,
radioactivity logs, and other available data were
used to prepare these maps as well as
to estimate representative values for porosity and
water saturation. When adequate data were available
and when circumstances justified, material-balance
and other engineering methods
were used to estimate OOIP and OGIP.
For those fields where the volumetric method was
applied, estimates of ultimate recovery were
obtained after applying recovery
factors to OOIP and OGIP. These recovery factors were based on consideration of the type of energy
inherent in the reservoirs, analyses of
the petroleum, the structural positions of the reservoirs,
and the production histories.
When applicable, material-balance and other engineering
methods were used to estimate recovery factors
based on an analysis of reservoir pressure and
reservoir fluid properties.
For depletion-type reservoirs or those whose performance
disclosed a reliable decline in producing-rate
trends or other diagnostic
characteristics, reserves were estimated by the application
of appropriate decline-curve or other performance
relationships. In the analyses of
production decline curves, reserves were estimated
only to the limits of economic production as defined
under the Definition of Reserves
heading of this report or to the limit of production
licenses as appropriate.
For the evaluation of unconventional reservoirs,
a performance-based methodology integrating the appropriate
geology and
petroleum engineering data was utilized for this report.
Performance-based methodology primarily includes
(1) production diagnostics, (2)
decline-curve analysis, and (3) model-based analysis
(if necessary, based on availability of data). Production diagnostics include
data quality
control, identification of flow regimes, and characteristic
well performance behavior. These analyses were performed for all well
groupings (or
type-curve areas).
Characteristic rate-decline profiles from diagnostic
interpretation were translated to modified hyperbolic
rate profiles, including one or
multiple b-exponent values followed by an exponential
decline. Based on the availability of data,
model-based analysis may be integrated to
evaluate long-term decline behavior, the effect of dynamic reservoir and fracture
parameters on well performance, and complex
situations
sourced by the nature of unconventional reservoirs.
In certain cases, reserves were estimated by incorporating
elements of analogy with similar wells or reservoirs
for which more
complete data were available.
Data provided by Equinor from wells drilled through October
31, 2021, and made available for this evaluation
were used to prepare
the reserves estimates herein. These reserves estimates
were based on consideration of monthly production
data available for certain
properties only through October 2021.
Estimated cumulative production, as of December
31, 2021, was deducted from the estimated gross
ultimate recovery to estimate gross reserves.
This required that production be estimated
for up to 2 months.
Oil and condensate reserves estimated herein are
those to be recovered by normal field separation. LPG
reserves estimated herein
consist primarily of propane and butane fractions and
are the result of low-temperature plant processing.
Oil, condensate, and LPG reserves
included in this report are expressed in millions of
barrels (10
6
bbl). In these estimates, 1 barrel equals 42
United States gallons.
Gas quantities estimated herein are expressed
as sales gas. Sales gas is defined as
the total gas to be produced from the
reservoirs after reduction for shrinkage from field or platform
handling, separation, processing (including liquid removal),
fuel usage, flaring,
reinjection, pipeline losses, and onshore processing
measured at the point of delivery. Gas reserves estimated herein are
reported as sales