How can you use pressure transient testing to optimize coalbed methane reservoirs?

1 What is PTT and why is it important for CBM reservoirs?

PTT is a process of injecting or producing fluid from a well and recording the pressure changes over time. By analyzing the pressure data, you can infer the reservoir behavior and parameters that affect the flow performance. PTT is important for CBM reservoirs because they have complex flow mechanisms that depend on the desorption of gas from the coal matrix, the dewatering of the cleats, and the compressibility of the gas and water. PTT can help you understand these mechanisms and optimize the well design, stimulation, and production strategies.

2 How to design a PTT for CBM reservoirs?

When designing a PTT for CBM reservoirs, you should consider the type of test, the duration, the frequency and accuracy of pressure measurements, and the wellbore and reservoir conditions. Depending on the objectives, reservoir conditions, and operational constraints, you can select from drawdown, buildup, interference, or pulse tests. The test should run long enough to capture different flow regimes and reach radial or pseudo-radial flow. Pressure should be measured at regular intervals with high precision to capture pressure trends and fluctuations. Additionally, you should account for effects of wellbore storage, skin, partial penetration, well interference, and boundaries on the pressure response.

3 How to analyze a PTT for CBM reservoirs?

Analyzing a PTT for CBM reservoirs requires analytical or numerical models that can simulate the pressure behavior of CBM reservoirs, taking into account the effects of gas desorption, cleat dewatering, and gas and water compressibility. Various methods can be used to analyze the PTT data, such as plotting the pressure and its derivatives on log-log or semi-log scales to identify flow regimes and their characteristics, fitting the pressure data to analytical solutions or type curves to estimate reservoir parameters like permeability, skin, drainage area, and boundaries, and using history matching techniques to adjust numerical model parameters until they match the pressure data.

4 How to use the results of a PTT for CBM reservoirs?

The results of a PTT for CBM reservoirs can provide valuable insights for optimizing reservoir management and performance. You can use the results to evaluate the reservoir potential and productivity, optimize well spacing and placement, design the optimal well completion and stimulation, adjust production rates and pressures to maximize gas recovery and minimize water production, and monitor reservoir performance to identify any changes or problems.

5 What are the challenges and limitations of PTT for CBM reservoirs?

PTT for CBM reservoirs is a powerful and useful technique, however, it has some challenges and limitations. These include the complexity and uncertainty of the reservoir models and parameters, which may require multiple tests and data sources to calibrate and validate. Interference and communication between wells may also affect the pressure response and the interpretation of the results. Additionally, operational and environmental constraints, such as equipment availability, personnel, resources, safety and regulatory issues, as well as disposal of produced water, should be taken into consideration.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?