A mixture of KHI (Kinetic Hydrate Inhibitor) and methanol has demonstrated significant success in preventing hydrate formation for gas wells within a Wyoming field. Prior to this treatment method being utilized, gas hydrate blockage formation, in surface flow lines and production equipment, was an operational risk and a costly source of downtime during flowback operations following hydraulic fracturing. The well start-up phase, following a shut-in period, was particularly hydrate-prone due to the higher pressure and lower temperature conditions created by the shut-in itself. Flowback of new high pressure wells through separation equipment, rather than to a pit or tank, also increased the likelihood of hydrate formation due to the presence of back-pressure. Increasing occurrence of hydrates was associated with the use of ‘Green Completion’ separation equipment, which was being used in order to comply with the Wyoming Department of Environmental Quality requirement that emissions associated with natural gas flaring and venting during fracturing flowback are to be minimized. Due to delays and mitigation costs resulting from surface hydrate blockages, the operator has estimated an overall increase in flowback costs of more than $500,000 for wells completed over a nine-month period using this ‘Green Completion’ approach.
KHI, methanol and controlled mixtures of both chemicals were all considered as potential hydrate prevention methods. Laboratory results suggest that mixtures of KHI and methanol are in fact a more cost-effective solution than methanol alone. In turn, the presence of methanol actually enhances the effectiveness of KHI at these high sub-cooling values of up to 20 °F.
During high pressure well start-up, KHI and methanol was injected into surface lines at rates of 5 to 10 gph, for a dosage rate of between 2 to 10% in the water phase. The inhibition was stopped once the production stream had warmed up to a temperature outside the stable hydrate formation region, usually within 4 hours of initiating the start-up. These injections required only minimal additional equipment in order to safely deploy the inhibition chemistry. Following the successful treatment of 11 wells, the KHI/methanol mixture has become the prevention technique of choice for this Wyoming gas field.
This work is particularly relevant to onshore US wells that are hydraulically fractured. Applicable Federal EPA requirements mandate that, starting January 2015, operators in all states must reduce VOC emissions during fracture flowback operations. Compliance with this requirement may increase the frequency of hydrate blockages, and this simple and cost-effective hydrate prevention technique offers significant benefit in these situations.