Yuanba Gas Field is one of the most difficult fields categorized as super-deep and HPHT reservoirs to develop in China. It’s buried in vertical depth (TVD) of more than 6700 m, and with pressure up to nearly 70MPa while temperature above 150oC, meanwhile, the average concentration of hydrogen sulfide and carbon dioxide are 5.14% and 7.5%. Well testing interpretations are hard for wells in this field because of phase segregation, and temperature effect on sour gas PVT especially if the wells are wellhead shut-in.
In this paper, the first horizontal well in Yuanba gas field is reviewed. The backflow pressure test and pressure buildup test were conducted in order to quantify the wells’ AOF and optimized daily rate. The test lasts for one week and one AOF of more than 6 million cubic meters is interpreted. However, severe temperature effect in wellbore is induced because the well is wellhead shut-in and the pressure & temperature gauge are located in wellhead. The testing was conducted in late autumn and the atmosphere temperature difference is as large as 20°C between day and night which caused severe pressure dilation. One well test interpretation model is built by taking atmosphere temperature dependent pressure dilation into consideration.
Results show that both the log-log plot of pressure & pressure derivative and the history match plot have good agreement with measured data after that the models convert the wellhead pressure into downhole pressure and implementing the ability of considering the pressure dilation caused by transient temperature. Without considering the temperature effect for super-deep wells, the wellhead pressure recording cannot truly converted into downhole pressure, which can not reflect the formation information and interpretation results are not believable. Using the new method, the weird well testing data for well-head shut-in wells can be interpreted.
The research is helpful for super-deep HPHT sour gas wells for wells and formation appraisal especially when the pressure and temperature gauge cannot be installed down into target layer. It can also be used to compare the commercial software models used for downhole pressure data.