Introduction to Reservoir Simulation

UNIVERSITI TEKNOLOGI PETRONAS

PCB3053 RESERVOIR MODELLING AND SIMULATION MAY 2015

Dr. Mohammed Abdalla Ayoub

Ch. 1.1: Introduction to Reservoir Simulation Petroleum Engineering Department (GPED)

Outline • Today’s class presentation will cover the following:

• Brief introduction about reservoir modeling and simulation. 1- Reasons to perform reservoir modeling. 2- Types of Computer Modeling 3- Simulation approaches. 4- Types of Numerical Models. 5- Modeling Concepts 6- Reservoir Simulation Steps. • Reservoir simulator classifications • Why it is accepted?. • Introduction To Commercial Reservoir Simulators

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Introduction Reservoir modeling Is often defined as the allocation of resources to optimize hydrocarbon recovery from a reservoir while minimizing capital investments and operating expenses.

• The primary objective in a reservoir management study is to determine the optimum conditions needed to maximize the economic recovery of hydrocarbons from a prudently operated field.

• Reservoir modeling is the most sophisticated methodology available for achieving the primary reservoir management objective. 3

Introduction, cont…, Reasons to perform a model study: • Several reasons to perform a model study. From a commercial perspective, is the ability to generate cash flow predictions. From two perspectives: 1- corporate impacts

 Cash Flow Prediction  Need Economic Forecast of Hydrocarbon Price 2-Reservoir Management  Maximize the economic recovery of hydrocarbon.  Minimize the operation expenses 4

Introduction, Cont…, Prediction of Future Performance Reservoir Simulation Model

Geological Model

History Matching

Reduce Operation Expenses Increase Recovery

Prediction

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Introduction, cont…, Need Data ! Available Data Not Enough Data: – – –

Analogy with other reservoirs Correlation Assumption

John, R. Fanchi Principles of Applied Reservoir Simulator 6

Integrated Model

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Introduction, cont…, Gridding • Honor geology • Preserve numerical accuracy • Be easy to generate

Gurpinar, 2001

Wolfsteiner et al., 2002

Prevost 2003 Khalid Aziz, Petroleum reservoir simulation

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Introduction, cont…, Reservoir Sampling and Scales Soft Data: Seismic Data related to interpretation Hard Data: Core and well log measurements

Conceptual scales: Giga scale

Include information associated with geophysical techniques, such as reservoir architecture

Mega scale

Deals with reservoir characterization and it includes well logging, well testing and 3D seismic analysis

Macro scale

Core analysis and fluid property analysis

Micro scale

Includes pore scale data obtained from techniques such as thin section analysis and measurement of grain size distribution 9

Introduction, cont…, Upscaling There are many techniques and levels, which are available for upscaling purpose. Make sure to select the best and optimum level of and techniques to minimize the associated errors Gurpinar, 2001

Khalid Aziz, Petroleum reservoir simulation

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Summary To summarize the need for reservoir simulation : • To obtain accurate performance predictions for a hydrocarbon reservoir under different operating conditions. • In a hydrocarbon-recovery project (which may involve a capital investment of hundreds of millions of dollars), the risk associated with the selected development plan must be assessed and minimized. Factors contributing to the risk: 1. The complexity of the reservoir because of heterogeneous and anisotropic rock properties; 2. Regional variations of fluid properties and relative permeability characteristics; 3. The complexity of the hydrocarbon- recovery mechanisms; and 4. The applicability of other predictive methods with limitations that may make them inappropriate (can be controlled through proper use of sound engineering practices and judicious use of reservoir simulation).

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Reservoir Simulator Reservoir simulators are computer programs that solve the equations for heat and mass flow in porous media, subject to appropriate initial and

boundary conditions. The number and type of equations to be solved depends on:  geological characteristics of the reservoir (single or double porosity),  characteristics of the oil, and

 oil recovery process to be modeled.

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Types of Computer Modeling The reservoir model

Fluid flow Equation within the reservoir. The reservoir is modeled by subdividing the reservoir volume into an array, or grid, of smaller volume elements, which called: gridblock, cell, or node.

The well model

Fluid flow that represents the extraction of fluids from the reservoir or the injection of fluids into the reservoir.

The well bore mode

Fluid flow from the sand face to the surface

The surface model

Constraints associated with surface facilities, such as platform and separator limitations.

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Simulation Approaches Broadly classified, there are two simulation approaches we can take: analytical (Physical) and numerical (mathematical).

 The analytical approach, as is the case in classical well test analysis, involves a great deal of assumptions—in essence, it renders an exact solution to an approximate problem.

 The numerical approach, on the other hand, attempts to solve the more realistic problem with less stringent assumptions—in other words, it provides an approximate solution to an exact problem. 14

The Simulation Process

Recovery process

Numerical Reservoir Simulation Process

Nonlinear PDE

Nonlinear Algebra Equations

Pressure, Saturation Distributions, and Well Rates

Solution starts here!!!

linear Algebra Equations

Types of Numerical Models Black oil Compositional Chemical flood Thermal Dual porosity (fracture) Gas model (gas gathering system)

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Types of Numerical Models, cont…,  Black oil model   o o

Depletion Water Injection Component: oil water gas Phase: Oil water gas

 Chemical model  Polymer and surfactant injection o Component: Water oil surfactant alcohol o Phase: Agues oleic micro-emulsion

 Compositional model        o o

Gas injection to increase or maintain reservoir pressure Miscible flooding as the injection gas goes into solution with oil Carbon dioxide flooding, with the gas soluble in both oil and water Thick reservoirs with a compositional gradient caused by gravity Reservoirs with fluid compositions near the bubble-point High-pressure, high temperature reservoirs Natural-fracture reservoir modeling. Component: C1,C2, ….So2, H2S, N2,.. Phase: Oil water gas

Modeling Concepts 1. Developing study objectives. 2. Develop or select an appropriate simulator. 3. Review, collect and estimate appropriate data. 4. Make preliminary runs to establish model parameters and limitations. 5. Match available history. 6. Predict performance under different operating scenarios.

7. Analyze results and prepare a report. 8. Plan additional work. 18

Reservoir Simulation Steps Essential steps in a simulator are: 1. Read input data (include reservoir description) 2. Initialize 3. Start time-step calculations • linearize equation, • start iteration loop (Newtonian iterations), • solve linear equations by direct or iterative methods, • test for convergence, and • repeat iterations if necessary. 4. Print and plot results at appropriate times 5. End if specified constraints are violated 6. Increment time and go to step 3 if end is not reached 7. End when run complete 19

Historical Developments Evolution of reservoir engineering and reservoir simulation is outlined in this section. The comments that follow are divided into three categories:

• Traditional Reservoir Engineering (1930 -) • Early Reservoir Simulation (1955 – 1970) • Modern Reservoir Simulation (1970 onward) 20

Reservoir Models Used: History of Simulation • Analogy

- Well Productivity - Recovery Factors - Reservoir Data

• Experimental

- measure the reservoir characteristics in the laboratory models - Scale these results to the entire hydrocarbon accumulations

• Mathematical

- Basic conservation laws and -

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constitutive equations Material Balance (continuity equation) Equation of motion (momentum equation) material balance+ decline curve+ statistical approaches+ analytical methods(pressure-transient and Buckley–Leverett methods) Finite Element Finite Difference

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Reservoir Simulator Classifications They can be classified in different approaches based on: 1. Type of reservoir fluids being studied (include gas, black oil, and compositional simulators) and the recovery processes being modeled (include conventional recovery (black oil), miscible displacement, thermal recovery, and chemical flood simulators). 2. The number of dimensions (1D, 2D, and 3D), the number of phases (singlephase, two-phase, and three-phase), and the coordinate system used in the model (rectangular, cylindrical, and spherical). 3. Rock structure or response (ordinary, dual porosity/permeability, and coupled hydraulic/thermal fracturing and flow). 22

Why it is accepted??? The widespread acceptance of reservoir simulation can be attributed to the advances in:

A.

computing facilities

B.

mathematical modeling

C.

numerical methods

D.

solver techniques, and

E.

visualization tools

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Eclipse Reservoir Simulator • Commercial reservoir simulator for over 25 years

• • • •

Black-oil Compositional Thermal Streamline

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Eclipse Reservoir Simulator 

Local Grid Refinement

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Gas Lift Optimization

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Gas Field Operations

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Gas Calorific Value-Based Control

Pseudo-Compositional EOR Foam EOR Polymer EOR Solvent

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Geomechanics

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Coalbed Methane

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Networks

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Reservoir Coupling

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Flux Boundary

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Environmental Traces

Unencoded Gradients

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Open-ECLIPSE Developer's Kit

Parallel ECLIPSE

EOR Surfactant Wellbore Friction Multisegmented Wells

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