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added Category:Methods in Exploration 10 using HotCat
* ø = [[porosity]] (decimal) from log and/or core data
* ø = [[porosity]] (decimal) from log and/or core data
* ''S''<sub>w</sub> = connate water saturation (decimal) from log and/or core data
* ''S''<sub>w</sub> = connate water saturation (decimal) from log and/or core data
* B<sub>oi</sub> = formation volume factor for oil at initial conditions (reservoir bbl/STB) from lab data; a quick estimate is ''B''<sub>oi</sub> = 1.05 + (''N'' × 0.05), where ''N'' is the number of hundreds of ft<sup>3</sup> of gas produced per bbl of oil [for example, in a well with a GOR of 1000, ''B''<sub>oi</sub> = 1.05 + (10 × 0.05)]
* B<sub>oi</sub> = formation volume factor for oil at initial conditions (reservoir bbl/STB) from lab data; a quick estimate is <math>B_{oi} = 1.05 + (N \times 0.05)</math>, where ''N'' is the number of hundreds of ft<sup>3</sup> of gas produced per bbl of oil [for example, in a well with a GOR of 1000, ''B''<sub>oi</sub> = 1.05 + (10 × 0.05)]
Another basic volumetric equation is
Another basic volumetric equation is
| Edge || 35–60
| Edge || 35–60
|-
|-
| Gravity || 50–70
| [[Gravity]] || 50–70
|}
|}
One general equation is
One general equation is
:Change in pore volume = Change in oil volume + change in free gas volume + change in water volume
:<math>\text{Change in pore volume} = \text{ Change in oil volume } + \text{ change in free gas volume } + \text{ change in water volume}</math>
where
where
* Change in pore volume = ''NB''<sub>oi</sub>/(1 – ''S''<sub>wi</sub>)''c''<sub>f</sub>''P''
* <math>\text{Change in pore volume} = \frac{NB_{oi}}{(1 - S_{wi})}c_fP</math>
* Change in oil volume = ''NB''<sub>oi</sub> –(''N'' – ''N''<sub>p</sub>)''B''<sub>oi</sub>
* <math>\text{Change in oil volume} = NB_{oi} - (N - N_p)B_{oi}</math>
* Change in gas volume = (''GB''<sub>gi</sub> – ''GB''<sub>g</sub>) + [''N''<sub>p</sub>''R''<sub>p</sub> ''(N'' – ''N''<sub>p</sub>) – NR<sub>si</sub>]''B''<sub>g</sub> due to gas produced, evolved, and encroached from a gas cap
* <math>\text{Change in gas volume} = (GB_{gi} - GB_g) + [N_p R_p (N - N_p) - NR_{si}] B_g</math> due to gas produced, evolved, and encroached from a gas cap
* Change in water volume = –''NB''<sub>oi</sub>''S''<sub>wi</sub>/(1 – S<sub>wi</sub>)''c''<sub>w</sub>''P'' – ''W''<sub>e</sub> + ''W''<sub>p</sub>''B''<sub>w</sub>, due to connate water volume change, encroached water, and produced water
* <math>\text{Change in water volume} = \frac{-NB_{oi}S_{wi}}{(1 - S_{wi})}c_wP - W_e + W_pB_w</math>, due to connate water volume change, encroached water, and produced water
where
where
The material balance technique for calculating gas reserves, like material balance for oil, attempts to mathematically equilibrate changes in reservoir volume as a result of production. The basic equation is
The material balance technique for calculating gas reserves, like material balance for oil, attempts to mathematically equilibrate changes in reservoir volume as a result of production. The basic equation is
:<math>\text{Weight (or SCF) of gas produced} = \text{ weight (or SCF) of gas initially in the reservoir} - \text{ weight (or SCF) of gas remaining in the reservoir}</math>
:<math>\text{Weight (or SCF) of gas produced} = \text{ weight (or SCF) of gas initially in the reservoir } - \text{ weight (or SCF) of gas remaining in the reservoir}</math>
The equations used to calculate OGIP are
The equations used to calculate OGIP are
===Reservoir simulation===
===Reservoir simulation===
The material balance method is actually a subset of the mathematical techniques that are available to modern petroleum engineers. Reservoir simulators use material balance as well as fluid flow equations to model the reservoir as a group of interconnected tanks. The advent of powerful computers has made the use of numerical simulation quite common for estimating reserves and recovery as well as initial volume in place. Since reservoir simulation can account for performance history through history matching, this method incorporates facets of all the techniques discussed. With sufficient data and prudent use of simulators, this method provides the best recovery estimates for complex reservoirs.
The material balance method is actually a subset of the mathematical techniques that are available to modern [[petroleum]] engineers. Reservoir simulators use material balance as well as fluid flow equations to model the reservoir as a group of interconnected tanks. The advent of powerful computers has made the use of numerical simulation quite common for estimating reserves and recovery as well as initial volume in place. Since reservoir simulation can account for performance history through history matching, this method incorporates facets of all the techniques discussed. With sufficient data and prudent use of simulators, this method provides the best recovery estimates for complex reservoirs.
==Production history analysis==
==Production history analysis==
* [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Original content in Datapages]
* [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=612 Find the book in the AAPG Store]
* [http://store.aapg.org/detail.aspx?id=612 Find the book in the AAPG Store]
* [http://www.aapg.org/science/discipline/business-and-economics/reserve-estimation#3547338-new-publications Reserves Estimation Articles]
[[Category:Reservoir engineering methods]]
[[Category:Reservoir engineering methods]]
[[Category:Methods in Exploration 10]]