Reservoir Engineering

[Buela_Vigneswaran]

Reservoir Engineering

3.1 Reservoir Characterization

• Rock Properties:
  • Porosity:
    • Measures the volume of void space in rocks available for fluid storage.
    • Types: Primary (original) and secondary (due to fractures or dissolution).
  • Permeability:
    • Indicates the ability of fluids to flow through rock pores.
    • Measured in darcies or millidarcies.
  • Net-to-Gross Ratio:
    • Proportion of reservoir rock to non-reservoir rock.
• Fluid Properties:
  • Reservoir Fluids:
    • Oil, gas, and water.
    • Classification of oil: Light, heavy, or bitumen.
  • PVT Analysis:
    • Pressure-Volume-Temperature studies to determine fluid behavior under reservoir conditions.
  • Fluid Contacts:
    • Oil-water contact (OWC) and gas-oil contact (GOC).

3.2 Reservoir Drive Mechanisms

• Primary Drive Mechanisms:
  • Solution Gas Drive: Pressure drops release dissolved gas from oil.
  • Water Drive: Aquifer water pushes hydrocarbons toward the well.
  • Gas Cap Drive: Expansion of gas cap displaces oil.
  • Gravity Drainage: Gravity moves hydrocarbons to the lower part of the reservoir.
  • Compaction Drive: Formation compaction due to pressure depletion.
• Recovery Efficiency:
  • Factors affecting recovery from each drive mechanism.
  • Combination of multiple drive mechanisms in real-world reservoirs.

3.3 Reserve Estimation Methods

• Types of Reserves:
  • Proved (P90), Probable (P50), and Possible (P10) reserves.
• Estimation Techniques:
  • Volumetric Method:
    • Calculates hydrocarbons initially in place (HIIP) using porosity, net thickness, and fluid saturations.
  • Material Balance Method:
    • Considers reservoir pressure changes over time to estimate reserves.
  • Decline Curve Analysis:
    • Uses production history to predict future performance.
  • Simulation Models:
    • Numerical models to estimate reserves and optimize recovery.

3.4 Enhanced Oil Recovery (EOR) Techniques

• Thermal EOR:
  • Steam injection and in-situ combustion to reduce oil viscosity.
• Chemical EOR:
  • Injection of polymers, surfactants, or alkalis to improve sweep efficiency.
• Gas Injection:
  • Use of CO₂, nitrogen, or natural gas to maintain pressure and displace oil.
• Microbial EOR:
  • Use of bacteria to reduce oil viscosity or improve mobility.
• Selection Criteria:
  • Reservoir characteristics, oil properties, and economic factors.

3.5 Fluid Flow in Porous Media

• Darcy’s Law:
  • Governs single-phase fluid flow in porous media.
• Multi-Phase Flow:
  • Interaction of oil, gas, and water phases.
  • Capillary pressure and relative permeability effects.
• Reservoir Pressure and Temperature:
  • Impact on fluid behavior and recovery methods.
• Reservoir Heterogeneity:
  • Effects of varying porosity, permeability, and fractures on fluid flow.

3.6 Reservoir Simulation and Modeling

• Purpose of Reservoir Simulation:
  • Predict future reservoir performance.
  • Optimize production strategies and field development plans.
• Types of Reservoir Models:
  • Black oil models (simple oil, gas, and water flow).
  • Compositional models (detailed fluid composition analysis).
  • Thermal models (used for thermal EOR methods).
• Data Integration:
  • Combining geological, petrophysical, and production data for accurate modeling.
• History Matching:
  • Adjusting simulation models to match historical production data.

3.7 Well Testing and Analysis

• Purpose of Well Testing:
  • Assess reservoir properties and performance.
• Types of Tests:
  • Pressure Build-Up Tests:
    • Measures reservoir pressure response after production stops.
  • Drawdown Tests:
    • Monitors pressure decline during production.
  • Interference Tests:
    • Assesses communication between wells.
• Analysis Techniques:
  • Use of diagnostic plots and pressure-transient analysis.

3.8 Field Development Planning

• Reservoir Development Strategies:
  • Optimal placement of wells (vertical, horizontal, or multilateral).
  • Selection of recovery methods (primary, secondary, or enhanced recovery).
• Well Spacing:
  • Balancing production efficiency with cost.
• Infrastructure Requirements:
  • Surface facilities, pipelines, and processing plants.

3.9 Decline Curve Analysis and Production Forecasting

• Decline Curve Types:
  • Exponential, hyperbolic, and harmonic declines.
• Applications:
  • Forecasting production rates and estimating reserves.
• Limitations:
  • Accuracy depends on quality of production data.

3.10 Economics of Reservoir Management

• Maximizing Recovery:
  • Balancing recovery efficiency with operational costs.
• Field Monitoring:
  • Use of real-time data (sensors, smart wells) to optimize production.
• Environmental and Regulatory Considerations:
  • Minimizing flaring and managing produced water.
  • Compliance with local and international regulations.