of 21
8/10/2019 Van Everdingen hurst Aquifers
1/21
8/10/2019 Van Everdingen hurst Aquifers
2/21
Aquifer
Water-bearing rocks surrounding nearly all hydrocarbon reservoirs.
Aquifer Size
Infinite in size
Finite In size
Larger than the oil/gas reservoirs they adjoin.
Negligible in their effect on reservoir performance.
Water Drive Reservoir
8/10/2019 Van Everdingen hurst Aquifers
3/21
8/10/2019 Van Everdingen hurst Aquifers
4/21
Aquifer Response Water InfluxWater Encroachment
Water Influx
Expansion of the water in the aquifer
Compressibility of the aquifer rock
Artesian flow
The water-bearing formation (Aquifer) outcrop is located
structurally higher than the pay zone.
8/10/2019 Van Everdingen hurst Aquifers
5/21
ReservoirAquifer Systems Classification
Degree of Pressure Maintenance
Outer Boundary Conditions
Flow Regimes
Flow Geometries
8/10/2019 Van Everdingen hurst Aquifers
6/21
ReservoirAquifer Systems Classification
Degree of Pressure Maintenance
The active water drive
The partial water drive
Water influx
Water influx
The limited water drive
Total Production Rate
Total Production Rate
Water influx Negligible
8/10/2019 Van Everdingen hurst Aquifers
7/21
ReservoirAquifer Systems Classification
Degree of Pressure Maintenance
Outer Boundary Conditions
Infinite Acting
The effect of the pressure changes at the
oil/aquifer boundary can never be felt at the
outer boundary
Finite Acting
Aquifer outer limit is affected by the influx into
the oil zone, i.e. pressure changes with time
8/10/2019 Van Everdingen hurst Aquifers
8/21
ReservoirAquifer Systems Classification
Degree of Pressure Maintenance
Outer Boundary Conditions
Flow Regimes
Steady State
Semi-Steady State
Unsteady State
Influence the rate of water influx into the reservoir
8/10/2019 Van Everdingen hurst Aquifers
9/21
ReservoirAquifer Systems Classification
Degree of Pressure Maintenance
Outer Boundary Conditions
Flow Regimes
Flow Geometries
Edge-Water Drive
Bottom-Water Drive
Linear-Water Drive
Essentially radial flow with
negligible vertical flow
Essentially radial flow with
significant vertical flow
Strictly linear flow
8/10/2019 Van Everdingen hurst Aquifers
10/21
8/10/2019 Van Everdingen hurst Aquifers
11/21
Water Influx Models
Mathematical models that simulate and predict aquifer performance
Most importantly, they predict the cumulative water influx history
Uncertainties
Rock and Fluid Properties
Geometry and Areal Continuity
Limitations
All Proposed Models need historical reservoir performance data
8/10/2019 Van Everdingen hurst Aquifers
12/21
Common Water Influx Models in Petroleum Industry
1. van Everdingen-Hurst
2. Carter-Tracy
3. Fetkovich
5. Schilthuis
6. Pot aquifer
4. Hurst modified
Unsteady State Models
More Realistic
More Complex
Capture Real Dynamics
Steady State Models
Simple Models
Approximate Solution
Far from Real Dynamics
8/10/2019 Van Everdingen hurst Aquifers
13/21
van Everdingen-Hurst Unsteady State Model
Genesis
Assumptions
Methodology
Procedure
Application
1949
Solution to diffusivity equation
Constant Terminal Pressure
Applying Laplace Transformation
Edge-water drive system
Bottom-water drive system
Linear-water drive system
8/10/2019 Van Everdingen hurst Aquifers
14/21
Material Balance Calculations with Water Influx in the Presence of
Uncertainty in Pressures
A technique for calculating the original amount of hydrocarbon in place
in a petroleum reservoir, and for determining the constants
characterizing the aquifer performance, based on pressure-production
data.
Based on a least-squares line-fitting computation was proposed by van-
Everdingen, Timmerman and McMahon in 1953
Their method would not work when there is error in the reservoir
pressure data even moderate error.
8/10/2019 Van Everdingen hurst Aquifers
15/21
gives reasonable answers when pressure data are uncertain to thedegree expected in reservoir pressure determinations
The major change introduced in the present analysis is to limit the least-
squares line-fitting to yield only one constant - the amount of
hydrocarbon in place
The water-influx constant is then taken as proportional to the oil (or
gas) in place
The constant of proportionality can be computed from estimates of
effective compressibility and reservoir water saturation.
Material Balance Calculations with Water Influx in the Presence of
Uncertainty in Pressures
8/10/2019 Van Everdingen hurst Aquifers
16/21
Material Balance Calculations with Water Influx in the Presence of
Uncertainty in Pressures
Commonly used least-squares analysis assumes all of the uncertainty to
be in the dependent variable.
The material balance should be arranged so that this condition is
fulfilled if correct inferences are to be made from statistical
calculations.
8/10/2019 Van Everdingen hurst Aquifers
17/21
MATERIAL-BALANCE COMPUTATIONS
Gas Res.:
Oil Res.:
van Everdingen and Hurst theory:
8/10/2019 Van Everdingen hurst Aquifers
18/21
ASSIGNMENT OF VARIABLES
consider that we have three variables which are linearly related
Gas-reservoir problem:
8/10/2019 Van Everdingen hurst Aquifers
19/21
8/10/2019 Van Everdingen hurst Aquifers
20/21
8/10/2019 Van Everdingen hurst Aquifers
21/21
