Study on prediction model of maximum hydraulic extension depth for ultra deep wells considering effects of temperature

How long the ultra deep well can extend and what is the ultra deep well’s maximum hydraulic extension depth are always concerned and studied by drilling engineers. The well’s maximum hydraulic extension depth can be predicted by the maximum hydraulic extension depth prediction model. To overcome the disadvantage that previous prediction model did not consider the effects of temperature and only applies to horizontal wells, a prediction model of maximum hydraulic extension depth for ultra deep wells considering effects of temperature is established. Considering the effects of temperature coupled with the constraints of drilling pump rated pressure and rated power, the prediction result of ultra deep well’s maximum hydraulic extension depth is modified. An ultra deep well developed by Sinopec in Shunbei oilfield, China, is analyzed, and its wellbore temperature profile and maximum hydraulic extension depth are analyzed and predicted. Results show that the maximum hydraulic extension depth with considering temperature is larger than that without considering temperature. With the identical depth, the higher inlet temperature and the greater geothermal gradient mean the higher drilling fluid temperatures in the drill string and annulus as well as the larger maximum hydraulic extension depth. Besides, the maximum depth decreases with the increase in drilling fluid flow rate and density, while it increases with the increase in drilling pump rated pressure and rated power. To ensure the designed depth can be reached, there exists the maximum drilling fluid flow rate and density, as well as the minimum drilling pump rated pressure and rated power. This study is important for accurately predicting the ultra deep well’s maximum depth within the limit capacity of drilling pump. In addition, it also plays a major role in avoiding drilling hazards.