Research and Field Test on Intelligent Injection of Mixed Natural Gas Hydrate Inhibitors

Abstract

Due to the severe winter climate conditions in northern China, gas wells and pipelines are at high risk of gas hydrate blockage. In order to ensure stable gas supply in winter, the required Methanol injection concentrations are as high as 30–60 wt% of water rates in Daqing gas wells. As increasing in the water-gas ratio, large quantities of Methanol are injected into wells through Methanol injection lines. However, there are some drawbacks in the current Methanol injection process, including huge Methanol consumptions, high operating costs, large loads of the pumping system, and long residence time of Methanol in injection pipelines. In addition, large amounts of Methanol injected into well bottom will inevitably affect the liquid entrainment capacity of gas wells. Therefore, to reduce Methanol injection quantities and improve the inhibitor injection efficiency, this paper carries out a research and field test on the intelligent injection technology of mixed natural gas hydrate inhibitors. The Kinetic Hydrate Inhibitor PVCap and Methanol are mixed to study methane hydrate formation temperature under the operating pressure of 5 MPa and rotating speed of 20 r/min. The results show that the critical temperature of hydrate formation can be reduced to 0.89 ℃ and induction time can be extended to 6330 s when 1 wt% PVCap and 5 wt% Methanol were mixed, which meets the safety transportation requirements between gas wells and gathering stations. Meanwhile, an intelligent inhibitor injection device has been developed, which can inject low dose mixed inhibitors continuously and can automatically adjust the injection rates by real-time monitoring and analyzing wellhead temperatures, pressures, and water productions. The technology has been tested in a hydrate-plugged gas well X. Before the test, the well cannot be opened, the opening time was 0 in 2018, which affected the annual production capacity of 450 × 104 m3. In the field test, the injection rates of the mixed inhibitors are 0–15 L/h, gas well X resumes production successfully. Compared with the traditional process, Methanol consumption is reduced by more than 80%. The manual replenishment cycle of inhibitors can be up to 15 days, and the maintenance workload is reduced by 93.3%, which is of great significance to the construction of the digital gas field in Daqing Oilfield.KeywordsGas wellsNatural gas hydrateBlockageInhibitorsIntelligent injection