CLASS 03
MATERIAL BALANCE FOR OIL FIELDS
MATERIAL BALANCE FOR OIL FIELDS
Definition of Terms
Before introducing the concept of material balance is important to define the basic terms are handled in the calculations.
N [MMstb]: refers to the volume of oil plus gas in solution, which was originally located at the site in standard conditions.
m (dimensionless): relationship between the volume of oil and gas layer over the gas dissolved in it. Is considered constant.
Np [MMstb] cumulative oil production in standard conditions.
Rp [CPN / BN]: gas ratio - Cumulative oil production in standard conditions.
Nβoi [MMBY]: refers to the volume of oil more gas in solution, which was originally located in the reservoir in reservoir conditions.
mNβoi [MMBY]: volume of free gas in the gas layer initially at reservoir conditions.
NRsiβoi [MMBY]: volume of gas dissolved in oil at reservoir conditions.
G [MMPCN]: total volume of gas found at the site originally, in standard conditions.
Each previously studied mechanism of production, contributes to the depletion of the reservoir.
Remember:
Before introducing the concept of material balance is important to define the basic terms are handled in the calculations.
N [MMstb]: refers to the volume of oil plus gas in solution, which was originally located at the site in standard conditions.
m (dimensionless): relationship between the volume of oil and gas layer over the gas dissolved in it. Is considered constant.
Np [MMstb] cumulative oil production in standard conditions.
Rp [CPN / BN]: gas ratio - Cumulative oil production in standard conditions.
Nβoi [MMBY]: refers to the volume of oil more gas in solution, which was originally located in the reservoir in reservoir conditions.
mNβoi [MMBY]: volume of free gas in the gas layer initially at reservoir conditions.
NRsiβoi [MMBY]: volume of gas dissolved in oil at reservoir conditions.
G [MMPCN]: total volume of gas found at the site originally, in standard conditions.
Each previously studied mechanism of production, contributes to the depletion of the reservoir.
Remember:
emptying = expansion of oil plus gas expansion solution + gas + gas cap expansion of water volume reduction connotes + porous + influx of water from the aquifer
This relationship is based on the principle known as the Law of conservation of matter by Lomonosov (1745) and Lavoisier (1789) which states that a chemical reaction the mass consumed by the reactants equals the mass of the products, so the mass is always conserved.
The left side of this expression is known as production and can be calculated as
Production
oil
solution gas expansion
Expansion oil + gas in solution
gas layer
connotes water expansion and pore volume reduction
Influence of water
The left side of this expression is known as production and can be calculated as
Production
Np ( βo + (Rp - Rs) βg) + Wp βw
The right side corresponds to the contribution of each mechanism can be calculated numerically as: Expansion oil
solution gas expansion
N [( βo + βg (Rsi - Rs)) - βoi]
Expansion
Expansion
gas layer
connotes water expansion and pore volume reduction
Influence of water
We
MATERIAL BALANCE EQUATION
The material balance is based mainly on the Law of Conservation of Mass and takes two important considerations.
1. The pressure is uniform throughout the reservoir.
2. The fluids are in thermodynamic equilibrium.
This method is used to determine the volume of oil originally in the reservoir, calculate and predict water inflow reservoir pressure. To apply you need to know the production history of the site and PVT data can be obtained using the methods already explained.
If we combine all the above terms, we find the general term deposits material balance.
Obviously, depending on the state of the reservoir properties, we can particularize the equation and find simplified expressions to suit our convenience.
For sites with a pressure is above the bubble pressure, any gas dissolved in oil (no expansion of the gas in solution or expansion of the gas cap), if we neglect the impact connoting water, and also not recorded surface water production, the material balance is as follows:
After the reservoir pressure reaches the bubble, the dissolved gas begins to be released and the compaction of pore volume and water connotes become negligible, will be two scenarios, the first corresponds to sites with no gas cap, in which we obtain the following equation:
If we have a layer of gas for same site:
is not always possible to keep track of all the requirements of the material balance equation. Because of this, some authors have worked with the equation and have managed to present some mathematical relations to find the same results in a simpler way.
Authors such as Van Everdingen (1953) and Havlena and Odeh (1963) were based on the grouping of variables, depending on others and in the plotting of these to subsequently linearize the parameters and more easily find the value of N, m G.
is important to identify the type of site with which it is working, and then properly grouping variables and use the linearization method.
In general, the line representing this method is as follows:
where
Classification of sites and related equations
Reservoir Volumetric + solution gas drive + compaction of pore volume
empuej Reservoir Volumetric gas + solution + gas layer
Push water + gas + solution pore volume compaction
Push gas water + solution + gas layer
water + gas Push solution
considered the most impotant mechanism contributing to the energy reservoir to produce hydrocarbons are:
1. Mechanism of depletion or gas in solution.
2. Drive mechanism of gas or gas cap expansion.
3. Water drive mechanism.
Using the terms defined in the beginning, the production rate of each mechanism can be calculated as:
1. The pressure is uniform throughout the reservoir.
2. The fluids are in thermodynamic equilibrium.
This method is used to determine the volume of oil originally in the reservoir, calculate and predict water inflow reservoir pressure. To apply you need to know the production history of the site and PVT data can be obtained using the methods already explained.
If we combine all the above terms, we find the general term deposits material balance.
Obviously, depending on the state of the reservoir properties, we can particularize the equation and find simplified expressions to suit our convenience.
For sites with a pressure is above the bubble pressure, any gas dissolved in oil (no expansion of the gas in solution or expansion of the gas cap), if we neglect the impact connoting water, and also not recorded surface water production, the material balance is as follows:
After the reservoir pressure reaches the bubble, the dissolved gas begins to be released and the compaction of pore volume and water connotes become negligible, will be two scenarios, the first corresponds to sites with no gas cap, in which we obtain the following equation:
If we have a layer of gas for same site:
METHOD STRAIGHT
is not always possible to keep track of all the requirements of the material balance equation. Because of this, some authors have worked with the equation and have managed to present some mathematical relations to find the same results in a simpler way.
Authors such as Van Everdingen (1953) and Havlena and Odeh (1963) were based on the grouping of variables, depending on others and in the plotting of these to subsequently linearize the parameters and more easily find the value of N, m G.
is important to identify the type of site with which it is working, and then properly grouping variables and use the linearization method.
In general, the line representing this method is as follows:
where
Classification of sites and related equations
Reservoir Volumetric + solution gas drive + compaction of pore volume
empuej Reservoir Volumetric gas + solution + gas layer
Push water + gas + solution pore volume compaction
Push gas water + solution + gas layer
water + gas Push solution
PRODUCTION INDEX
Other authors who have worked on the basis the material balance equation to determine the influence of each mechanism of production and energy each brings, so it is possible to determine which mechanism is more efficient at each site. Pirson considered the most impotant mechanism contributing to the energy reservoir to produce hydrocarbons are:
1. Mechanism of depletion or gas in solution.
2. Drive mechanism of gas or gas cap expansion.
3. Water drive mechanism.
Using the terms defined in the beginning, the production rate of each mechanism can be calculated as:
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