Pressure Transient Analysis (PTA) is a sophisticated method for interpreting well and reservoir performance based on the analysis of pressure changes over time. Here’s a simplified overview of how a pressure transient analysis is typically conducted:

  1. Data Collection: The first step involves collecting pressure data from a well after a production or injection change. This can be initiated by a well shut-in, a change in production rate, or starting/stopping an injection. The pressure is measured at the wellbore, and the data collected over time reflects how the reservoir responds to the change.
  2. Pressure Buildup or Drawdown Test: Depending on the test, the well may be shut in after a period of production (pressure buildup test) or opened to produce at a measured rate (drawdown test). In a buildup test, the well is closed, and the pressure increase is recorded. In a drawdown test, the well is opened, and the decrease in pressure is observed.
  3. Data Analysis:
    • Plotting: The collected pressure data and time are plotted on specific types of graphs, such as semilog plots or diagnostic plots, to identify trends and anomalies.
    • Type Curves: These plots are compared against standard or generated type curves that represent theoretical reservoir responses, helping to match the observed data with known reservoir behaviors.
  4. Interpretation: Using various models and equations, such as the Horner plot method for buildup tests or the Agarwal-Gardner method for drawdown analysis, the data is interpreted to extract key reservoir characteristics such as:
    • Permeability
    • Skin factor (damage or enhancement near the wellbore)
    • Reservoir boundary effects
    • Boundary distances
    • Reservoir pressure
  5. Software and Models: Specialized software and analytical/numerical models are often used to process the data, fit curves, and interpret the results. This allows for the estimation of reservoir properties and the assessment of well performance.
  6. Application of Results: The insights gained from PTA are used to make decisions on reservoir management, well completions, stimulation requirements, and production optimization.