Well testing helps determine the reservoir’s capability to produce hydrocarbons—especially in reservoirs with high gas-to-oil ratio (GOR)—and provides data on:
Reservoir pressure and temperature
Permeability and skin factor
Fluid composition and phase behavior
Productivity index and deliverability
Wellbore and reservoir behavior under dynamic conditions
Challenges of High-Gas Content:
Phase behavior: Gas expands rapidly when pressure drops, affecting flow measurements.
Flow instability: High gas rates can cause slug flow or unstable multiphase flow.
Separation issues: Efficient separation of gas and liquid phases at surface facilities is required.
Measurement accuracy: Gas is compressible and flow rates can fluctuate, making accurate metering difficult.
Safety risks: High gas volumes increase the risk of flammable releases or blowouts.
Testing Techniques Used
Drill Stem Test (DST): Temporarily isolates the formation to measure pressure and flow—particularly useful for early reservoir evaluation.
Production Testing: Measures flow after completion using surface production equipment.
Multi-rate Testing: Determines inflow performance and assesses reservoir boundaries.
Build-up/Drawdown Tests: Evaluate pressure behavior after flow stops or starts.
Key Parameters in High-Gas Well Tests
Gas flow rate (MMscf/day)
GOR (Gas-Oil Ratio): Determines if the reservoir is gas-dominant or oil-dominant.
Wellhead and bottom-hole pressures
Reservoir temperature
Condensate yield (in gas condensate reservoirs)
Interpretation Considerations
Use PVT (Pressure Volume Temperature) analysis for accurate modeling of gas behavior.
Two-phase flow models are essential to interpret test data (e.g., gas-liquid interaction).
Identify condensate banking near the wellbore, which can reduce gas productivity.
Analyze skin effect and reservoir boundaries more carefully due to high mobility of gas.
Safety and Environmental Concerns
Use of blowout preventers (BOPs) and flare systems.
Monitor for H2S or other toxic gases.
Proper gas flaring or reinjection to reduce environmental impact.