A Successful Methanol Treatment in a Gas-Condensate Reservoir: Field Application

摘要

A field test was conducted to investigate the effectiveness ofmethanol as a solvent for removing condensate banks thatform when pressure in the near wellbore region falls below thedewpoint. Core flood experiments on Texas CreamLimestone and Berea cores show that condensateaccumulation can cause a severe decline in gas relativepermeability, especially in the presence of high watersaturation. This can result in well productivity declining by afactor of 3 to 5 as bottom hole pressure declines below thedewpoint. PVT analysis performed on field samples takenfrom the Hatter’s Pond field in Alabama indicate retrogradecondensate behavior. These high-temperature deep gas wellsshow low gas productivity and large skin. A preliminaryanalysis of the data indicated the possibility of condensate andwater blocking due to the loss of water-based drilling fluids.Core samples were used to measure gas relative permeability.Compatibility tests were conducted to ensure that the injectionof filtrate and methanol did not cause any damage to the core.Since the formation brine is very saline, tests were conductedto check for salt precipitation during methanol injection.Based on these laboratory results and a single-well numericalsimulation, a field test was conducted. The well chosen fortreatment was producing 250 MSCFPD with 87 BPD ofcondensate. A thousand barrels of methanol was pumpeddown the tubing at a rate of 5 to 8 B/min. Gas productionincreased by a factor of 3 initially and stabilized at about 500MSCFPD. Condensate production doubled to 157 BPD. Thewell shows a skin of –1.9 after methanol treatment. Theincrease in gas and condensate production was observed topersist more than 10 months after the treatment.Several possible explanations are provided for the positiveresults obtained in this test. Some general conclusions aremade for the design for future treatments.