Abstract:

The evaluations of properties of carbonate reservoirs containing gas with very high carbon dioxide (CO2) content often face many difficulties. In fact, there is a significal difference in interpretation results compared to conventional gas well testing due to: there is a gas to liquid phase transition; noise, abnormal increase or decrease in pressure and temperature during flow period, etc. These abnormal behaviors are all directly related to the specificity of CO2 properties with high compressible than that of natural gas, which can vary greatly density and can reach supercritical liquid state, transitioning solid to liquid or liqid to gaseous states even when pressure and temperature changes within a small range. During the testing of gas wells with high CO2 content, the phenomenon of pressure drop while pressure buid-up often occurs, leading to the analysis of reservoir parameters according to the conventional pressure build-up analysis method usually not feasible. The content of the article is aimed at researching and applying the method of interpreting well test data in the drawdown period while multi-rate flowing to more accurately estimate reservoir properties and mitigate risks in the design of the field development plan to achieve the economic efficiency.