Vertical Lift Models Substantiated by Statfjord Field Data (SPE 154803)

The Statfjord field entered into the blowdown phase after 30 years of production. Production of injection gas and gas liberated from residual oil is the main production target in this phase. In some areas, the gas cap has been produced and the wells are producing mainly water until the solution gas is mobilized. These wells have gone through large changes in GLR and WCT. Production tests from wells located in such areas have been used when analysing the ability of multiphase-flow correlations to model vertical lift performance (VLP). Accurate modelling of the VLP is critical to predict a realistic production rate during the blowdown phase. Measured wellhead (THP) and downhole pressures from 203 production tests, from six wells, were used to analyse the accuracy of VLP correlations at widely varying flow conditions (GLR, WCT, and THP). Altogether 17 partly well-known, multiphase pressure drop correlations incorporated in the program Prosper were tested by comparing observed and calculated downhole pressures. Based on the production tests the ability of the different correlations to predict the VLP varies with the following top 3: Petroleum Experts, Petroleum Experts 2, and Petroleum Experts 3. These correlations are recommended if no measured data is available. In general too low pressure drops were predicted at low gas-liquid ratio (GLR), and too high pressure drops at high GLR. After tuning, accurate predictability was observed for the different correlations for limited ranges in GLR e.g. 50-300 Sm3/Sm3. However, for larger ranges in GLR it was not possible to achieve an accurate VLP correlation even after tuning. The error in the predicted production performance when a single VLP correlation is used can be substantial for highly productive wells with large variations in producing GLR. It is recommended to shift the tuning following the GLR development.