Investigation of Gas-Lift Mitigation in Deepwater Pipeline-Riser System

Abstract

Slugging studies done recently have shown that slug mitigation techniques need to be improved, particularly in deepwater scenarios. In order to breakup the liquid slugs inside the riser and reduce acute slugging, the gas-lift slug mitigation method involves injecting a pre-determined volume of gas at the pipeline-riser section. Through OLGA severe slug mitigation; the study investigated various positioning of the gas-lift upstream of the riser-base. A case-study of a typical deepwater scenario within West-Africa was considered. The field was located at a water-depth of over 1000m with riser height of 1513m and pipeline section of 2712m which were all modeled on OLGA. The study involved validation of the pressure simulated against initial pressure behavior from the field. The field case involved running well X1 set up at about 72°C and mass flow rate of 3.25 kg/s, well X2 set up at about 70°C and 12.13 kg/smultiphase flow stream flow. Gas-lift was deployed within range of 7kg/s to 35 kg/s. Although severe slugging was mitigated, the power consumption required by required by gas-lift technique proved to be relatively high. The results indicated that gas-lift was better off closer to the supporting wells than being at the riser-base; as with the scenario of 35 kg/s gas-lift closer to well X2, the gas pressure upstream of the riser-base was significant enough to push off liquid slugs that accumulated at the riser-base; giving rise to a more stable flow and moderating the severe slugging scenario.