Enhanced Oil Recovery in High Viscous Reservoir Using the Thermal Process
CHAPTER ONE
Objectives
Below are the outlined objectives for the work:
- To derive and solve a heat equation for conduction with a heat source using finite difference method.
- Using a viscosity correlation, predict the viscosity dependence on temperature for a high viscous volumetric oil
- To derive and solve diffusivity equation for single phase flow using finite difference method.
- To develop a 3-D numerical simulator for high viscous oil reservoir combining the heat, viscosity and diffusivity equations using
- To use the developed simulator to predict temperature distribution and pressure
CHAPTER TWO
LITERATURE REVIEW
- Natural Drive Mechanism
Each reservoir is composed of a unique combination of geometric form, geological rock properties, fluid characteristics, and drive mechanism (primary). The recovery of oil by any of the natural drive mechanisms is called primary recovery thus no energy supplement. Although no two reservoirs are identical in all aspects, they can be grouped according to the primary recovery mechanism by which they produce (Ahmed 2006). There are basically six driving mechanisms that provide the natural energy necessary for oil recovery:
- Depletiondrive (This type of drive has its main source of energy being due to gas liberation from the crude oil and expansion of the solution gas as the reservoir pressure is )
- Gas cap drive (This drive is identified by the presence of a gas cap with little or no water drive. The reservoir pressure decline is slow due to the ability of the gas to)
- Water drive (Most reservoirs are bounded on a portion or all the edges by water bearing rocks called aquifers. These aquifers help provide energy to push the hydrocarbons.There are bottom water and edge water occurring in this )
- Gravity drainage drive (This drive is as result of differences in densities of the reservoir fluids)
- Combination drive (This drive can chain two or more of the abovedrives)
Rock and Liquid Expansion Drive
Expansion occurs as the reservoir undergoes a pressure depletion. In such conditions when no external influx is present, the reservoir fluid essentially displaces itself. For under saturated oil reservoirs, the liquid phase expansion contributes only a little to oil recovery, since oil compressibility is usually very low, especially in medium to heavy gravity oils.
In under saturated oil reservoirs producing by rock and fluid expansion, the pressure declines very rapidly due to the rock and liquid being slightly compressible while the producing Gas-Oil-Ratio (GOR) remains constant. Fluid and rock expansion is naturally the least efficient drive mechanism for oil reservoirs especially heavy oil reservoirs and thus the need to supplement with external energy sources.
CHAPTER THREE
METHOD USED
- Development of the Simulator
The following itemized stages were used in developing the three dimensional numerical oil reservoir simulator:
- Derive a heat partial differential equations of the model by conduction based on the rock and fluid properties of the
- Discretize the derived heat diffusion equations in both space and time to obtain a system of linear
- Establish the stability of the equations using the Crank Nicolson
- Write Codes for the discretized equations using MATLAB
- Couple the temperatures from the heat model with a viscosity model using MATLAB Programming.
- Derive a diffusivity partial differential equations for an expansion drive
- Discretizethe derived diffusivity equation in both space and time to obtain another system of
- Establish these equations’ stability using Crank Nicolson
- Write Codes for the systems of equations using MATLAB
- Validate the simulator using Base case
In the development of this reservoir simulator, three main models were used; Mathematical model, Numerical model and Computer model (MATLAB code)
CHAPTER FOUR
RESULTS AND DISCUSSION
This chapter focuses on the plots of temperature, viscosity and pressure both in 2D and 3D and their analysis. This model was run using a grid size of 11*11*11 since the computer storage was too small to run a higher grid size.
Base Case Scenario
The model is run firstly without any heat source to observe the bottom-hole and average pressure in the reservoir that is, no change in temperature and viscosity. Figure 4.1 shows that the average reservoir pressure (Pav) is higher than the bottom-hole flowing pressure (Pwf) thus there being production. It can also be observed that both pressures decline with time. It is expected that for a volumetric reservoir, the pressure decline would be rapid over time.
CHAPTER FIVE
CONCLUSION AND RECCOMMENDATION
- Conclusion
In this work, a three dimensional numerical simulator for high viscous volumetric reservoir is developed. Key reservoir parameters such as temperature, viscosity, pressure and average pressure were evaluated using the developed simulator. The average reservoir pressure is determined as the weighted average. 2D plots of temperature, viscosity and pressure behavior with the introduction of a heat source over time were generated. Surface plots of the temperature increase, viscosity decrease and pressure depletion were generated considering some selected cells in the reservoir. Temperature plots showed a rise which was either rapid or gradual due to the amount of heat source introduced. Viscosity plots also showed a rapid or gradual decline depending on the effect from temperature which indicates an increase in mobility thus enhancing the hydrocarbons’ sweep efficiency. Pressure behavior showed a slower pressure decline than the base case which has no heat addition thus pressure being sustained due to decrease in oil viscosity. The pressure behavior agrees with what literatures have proposed about enhanced oil recovery being used to maintain pressure and extend reservoir production life.
- Recommendations
In order to make the developed simulator efficient, the following recommendations were made;
- Further studies should be done to analyze the effect of varying thermal properties with temperature such as thermal conductivity, specific heat capacity and density of thesystem since they are not
- Change in temperature result in thermal expansion which affect the compressibility of the system which in turn affect the formation volume factor, permeability and porosity of the reservoir thus further studies can be made in evaluating the effect of varying compressibility, formation volume factor, permeability and
- Numerical methods such as finite element method, finite volume method, integral volume and variation method could be employed instead of the finite difference method used in this study for the discretization of the partial differential equation governing the whole system. This will accommodate both regular and irregular reservoir
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