Coalbed Methane Well Productivity Determination Without Shutdown
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Solution Overview
Problem
Conventional methods for determining the deliverability equation of coalbed methane wells without shutting down the well are difficult to apply due to the requirement of maintaining constant formation pressure and stabilized seepage state, which is challenging in coalbed methane wells with low permeability, leading to significant changes in formation pressure and prolonged stabilization times.
Innovation Solution
A method involving obtaining coalbed methane PVT experimental data, performing stabilized bottomhole flow pressure tests under constant production conditions, determining a relationship between pressure and pseudo-pressure, and iteratively calculating formation pressures using a binomial deliverability equation to determine the productivity of the well without shutting it down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional well test method is used to determine deliverability equation, then measurement precision is improved, but productivity is reduced due to well shutdown
Solution Approach 1:
The patent enables continuous production testing without well shutdown by using material balance equations to calculate formation pressure changes during production. This allows the deliverability equation to be determined while the well remains in continuous production mode, eliminating the need to stop production for pressure buildup tests.
2Productivity
If conventional method without shutdown is used, then productivity is maintained, but measurement precision deteriorates due to formation pressure changes
Solution Approach 1:
The patent uses material balance equations to continuously calculate formation pressure based on cumulative production data, creating a feedback mechanism that accounts for pressure changes during production. This allows accurate deliverability equation determination despite formation pressure varying during the test period.
Solution Approach 2:
The patent transforms the approach by using pseudo-pressure and material balance relationships to account for formation pressure changes. Instead of requiring constant formation pressure, the method incorporates pressure changes into the calculation framework through iterative solutions of the deliverability equation.
3Measurement precision
If stabilized flow pressure test is performed under multiple production conditions, then measurement precision is improved, but loss of time increases due to stabilization period
Solution Approach 1:
The patent uses preliminary production data and material balance calculations to estimate formation pressure at different production stages, eliminating the need to wait for full stabilization. By performing preliminary calculations based on cumulative production, the method determines deliverability parameters without requiring complete stabilization at each test point.
4Measurement precision
If well shutdown is performed for conventional testing, then measurement precision is improved, but ease of operation deteriorates due to water flooding issues
Solution Approach 1:
The patent maintains continuous production throughout the testing process, eliminating well shutdowns that cause water flooding problems. By using material balance equations to account for pressure changes during continuous production, the method avoids the operational difficulties of shutting down and restarting high-volume fracturing wells.
Data Source
AI summary
A method for determining a productivity of a coalbed methane well without shutting down the well includes steps of: obtaining coalbed methane basic data; based on PVT experimental data, determining a relationship table between a pressure and a coalbed methane deviation factor, and a relationship table between the pressure and a pseudo-pressure; recording daily gas production rates, bottomhole flow pressures, and cumulative gas productions at each stabilized flow pressure test moment in at least three different production stages; determining formation pressures corresponding to each stabilized flow pressure test moment based on a material balance equation; according to the formation pressures, the bottomhole flow pressures and the production rates, determining coefficients in a deliverability equation of the coalbed methane well for determining the deliverability equation; substituting the formation pressures and the bottomhole flow pressures into the deliverability equation for obtaining corresponding productivity.