Entropy generation minimization for enhancing the fluid recovery and energy efficiency in petroleum reservoirs

Elhaj, Murtada A. (2021) Entropy generation minimization for enhancing the fluid recovery and energy efficiency in petroleum reservoirs. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Hydrocarbon reservoir fluids usually contain a significant amount of mechanical energy that depends on the distribution of temperature and pressure throughout the reservoir. A fraction of the fluid's useful energy is lost during the irreversible processes that occur throughout the production life of the reservoir. Entropy generation (or production) can characterize this loss of useful energy in petroleum reservoirs. A petroleum engineer can develop an appropriate production strategy that minimizes entropy production in a reservoir to promote the efficient use of the reservoir energy. The design of a poor reservoir production system might result in a short-lived production well, low reservoir recovery factor, and inefficient use of available resources. Such an issue would not only result in the loss of a valuable portion of the reservoir's useful energy but also financial benefits. Various forms of energy exchange occur during hydrocarbon production in reservoirs, e.g., fluid and rock expansion, fluid flow, gravity drainage, and compaction of poorly consolidated rocks. During a reservoir's production lifetime, irreversible processes (e.g., fluid friction and heat transfer) lead to waste of energy, reducing the overall system's operational efficiency. Therefore, there is a desire to select an appropriate design that minimizes the entropy generation. In this thesis, we investigate the effect of essential factors such as reservoir formation, reservoir fluids, and production rate on entropy generation. The ultimate goal is to design a reservoir production strategy using the entropy generation analysis such that the production efficiency can be maximized. To simulate the fluid flow behavior of a reservoir system, a pseudo-steady flow state is developed in this thesis for single-phase (dry gas) and two-phase (oil-water) flow models in both the wellbore and reservoir. The effect of the wellbore conditions on the single-phase models is investigated and analyzed. One-dimensional flow is assumed in the wellbore, whereas radial flow occurs in the reservoir. Mass, momentum, energy, and entropy balance equations, including a method of Entropy Generation Minimization (EGM), are used to address the fluid flow behavior and energy loss in wellbore and reservoir systems. For a single-phase flow, the near-wellbore region is investigated and considered to be a separate zone for model development, which allows flexibility in modelling skin effects near the wellbore. Numerical methods are used to solve the fluid flow and entropy equations. The models are solved by a numerical scheme programmed in the MATLAB environment with an appropriate algorithm. For validation purposes, a commercial simulator, Computer Modeling Group (CMG), is used to verify the predicted results. A new production performance criterion called the Coefficient Of Performance (COP) is introduced. The COP integrates the recovery factor with entropy generation and provides a quantitative measure to optimize reservoir production. The models are used to conduct a parametric sensitivity analysis that includes the effects of fluid and rock parameters, such as permeability, porosity, viscosity, skin factor, Bottom Hole Pressure (BHP), wettability, and temperature on the total entropy production. The COP is used to optimize the operating conditions of the reservoir, such as the production rates and BHP. It is found that permeability and BHP have the most impact on the total entropy production for single-phase models. Concurrently, temperature and wettability are essential factors for two-phase flow models. This thesis enhances the understanding of reservoir energy analysis and provides more accurate models for calculating the optimum production rate of a given reservoir. In particular, the results presented in this thesis will impact production history calculations and reservoir simulation results. Furthermore, this research provides practitioners and engineers in the petroleum industry with a useful alternative approach for maximizing recovery efficiency by minimizing entropy generation.

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