How does well testing contribute to production surveillance and performance evaluation? Explain the different types of well tests and their applications.

Well testing plays a crucial role in production surveillance and performance evaluation in the oil and gas industry. It involves the measurement and analysis of pressure, flow rates, and fluid properties to gather valuable data about the reservoir, wellbore, and production system. Well tests provide critical insights into reservoir behavior, well performance, and the effectiveness of production strategies. Let's explore the different types of well tests and their applications:

1. Drill Stem Test (DST):
A drill stem test involves temporarily isolating a specific zone in the reservoir to evaluate its productivity. It is typically conducted during the drilling phase or early production stages. DSTs provide information about reservoir pressure, fluid properties, permeability, and deliverability. This data helps estimate the reservoir's potential and determine the need for further production infrastructure.
2. Well Flow Test:
Well flow tests involve measuring flow rates and pressures during production operations. They provide valuable data on well performance, including productivity, pressure drawdown, skin damage, and the presence of near-wellbore issues. By analyzing flow test data, engineers can evaluate well deliverability, estimate reservoir properties, optimize production rates, and assess the need for artificial lift methods.
3. Build-Up Test:
A build-up test is conducted by shutting in the well and monitoring the pressure buildup over time. This test helps determine reservoir pressure, permeability, skin damage, and boundaries. It provides insights into reservoir connectivity, reservoir fluid properties, and the presence of any barriers or faults affecting well performance. Build-up tests are crucial for accurate reservoir characterization and determining the need for reservoir management strategies.
4. Production Logging:
Production logging involves deploying specialized tools into the wellbore to measure fluid flow rates and assess the vertical distribution of fluids. It helps identify the contribution of different intervals or zones, detect fluid entries or crossflows, and evaluate wellbore conditions such as fluid holdup and flow regime. Production logging assists in optimizing production strategies, diagnosing wellbore issues, and evaluating the efficiency of artificial lift systems.
5. Pressure Transient Analysis:
Pressure transient analysis is used to analyze the transient behavior of pressure changes in the reservoir during well testing or shut-in periods. It provides insights into reservoir properties, such as permeability, skin damage, and boundaries. By analyzing pressure transient data, engineers can estimate reservoir parameters, evaluate reservoir performance, and optimize production strategies.
6. Injection Tests:
Injection tests involve injecting fluids, such as water or gas, into the reservoir to assess reservoir characteristics and fluid displacement behavior. These tests provide valuable information on reservoir properties, injectivity, reservoir sweep efficiency, and the effectiveness of water or gas flooding techniques. Injection tests assist in designing and optimizing enhanced oil recovery (EOR) projects.
7. Interference Tests:
Interference tests involve monitoring pressure responses in multiple wells to evaluate reservoir connectivity and determine reservoir properties. By analyzing pressure interactions between wells, engineers can assess reservoir boundaries, permeability, and heterogeneity. Interference tests are valuable for reservoir characterization, determining well spacing, and optimizing production strategies.

Each type of well test provides specific insights into reservoir behavior, well performance, and production system efficiency. By conducting and analyzing these tests, reservoir engineers can make informed decisions regarding reservoir management, production optimization, artificial lift selection, and enhanced oil recovery techniques. Well testing is an integral part of production surveillance and performance evaluation, enabling operators to maximize hydrocarbon recovery and ensure the long-term productivity of oil and gas fields.