A Successful Methanol Treatment in a Gas/condensate Reservoir: Field Application
- Hamoud A. Al-Anazi (Saudi Aramco) | Jacob G. Walker (DeGolyer and MacNaughton) | Gary A. Pope (U. of Texas at Austin) | Mukul M. Sharma (U. of Texas at Austin) | David F. Hackney (ChevronTexaco)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Facilities
- Publication Date
- February 2005
- Document Type
- Journal Paper
- 60 - 69
- 2005. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6.9 Coring, Fishing, 3.3.1 Production Logging, 3.1.6 Gas Lift, 4.6 Natural Gas, 2.2.2 Perforating, 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene, 4.1.2 Separation and Treating, 5.4.3 Gas Cycling, 3 Production and Well Operations, 5.8.8 Gas-condensate reservoirs, 5.2 Reservoir Fluid Dynamics, 2.7.1 Completion Fluids, 1.6 Drilling Operations, 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 4.3.4 Scale, 4.2.3 Materials and Corrosion, 5.5 Reservoir Simulation, 1.8 Formation Damage, 5.6.4 Drillstem/Well Testing
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A field test was conducted to investigate the effectiveness of methanol as a solvent for removing condensate blockage.On the basis of laboratory results and a single-well numerical simulation, a field test was conducted on a gas well that suffered from gradual productivity decline caused by condensate banking in the Hatter's Pond field in Alabama.The well chosen for treatment was producing 250 MMscf/D of gas with 87 BOPD of condensate.After methanol treatment, both gas- and condensate-production rates increased by a factor of two over the first 4 months and by 50% thereafter.
Gas production from reservoirs having a flowing bottomhole pressure (BHP) lower than the dewpoint pressure results in the accumulation of a liquid hydrocarbon near the wells.This condensate accumulation, sometimes called condensate blocking, reduces the gas relative permeability and, thus, the well's productivity.Condensate saturations near the well can reach as high as 50 to 60% under pseudosteady-state flow of gas and condensate.1Even when the gas is very lean, such as in the Arun field with a maximum liquid dropout of 1.1%, condensate blocking can cause a large decline in well productivity.2-4The Cal Canal field in California showed a very poor recovery of 10% of the original gas in place because of the dual effect of condensate blocking and high water saturation.5
Several methods have been proposed to restore gas-production rates after a decline caused by condensate and/or water blocking.6-9 Gas cycling has been used to maintain reservoir pressure above the dewpoint.Injection of dry gas into a retrograde gas/condensate reservoir vaporizes condensate and increases its dewpoint pressure.8 Injection of propane was experimentally found to decrease the dewpoint and vaporize condensate more efficiently than carbon dioxide.10 Inducing hydraulic fractures into the formation can increase the BHP.While hydraulic fracturing has been used to enhance gas productivity, it is not always feasible or cost-effective5,11; however, hydraulic fracturing successfully restored the gas productivity of a well that died after the flowing BHP dropped below the dewpoint.12
Recently, a new strategy of using solvents was developed to increase gas relative permeability reduced by condensate and water blocking.7,9Al-Anazi et al.9 found that methanol was effective in removing both condensate and water and restored gas productivity in both low-permeability limestone cores and high-permeability sandstone cores.Gas productivity decreased to approximately the same extent in both low- and high-permeability cores because of condensate blocking.After methanol treatment, an enhanced-flow period is observed in both low- and high-permeability cores.Condensate accumulation is delayed for a certain time.During this time, the productivity index is increased by an order of magnitude in both low- and high-permeability cores.The duration of the enhanced flow period is controlled by the volume of methanol injected and its rate of mass transfer into the flowing gas phase after treatment.Methanol treatments remove both water and condensate by a multicontact miscible displacement, if sufficient methanol is injected.
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