Innovative Approach to Increase Productivity of Gas Condensate Reservoirs
Halliburton Offshore Services inc., Mumbai, India.
Gas condensate reservoirs are an important source of gas and condensates in the modern day. But production from gas condensate reservoirs presents a plethora of problems.Improper pressure maintenance and Retrograde condensation leaves 30-60% of condensates permanently in the reservoir.Another problem is that Gas cycling may be uneconomical in low condensate content reservoirs.Two methods are being suggested in this paper to improve gas condensate reservoir production. These are intelligent production technique and microbial action.
The intelligent production system will use a feedback control loop to optimize production . Initially the reservoir is simulated using a compositional simulator. A production vs time chart should be established using these simulations while taking care that the reservoir doesn't produce too much condensates in the reservoir. This production vs time chart can be uploaded into a control system hardware to control valves in the production string intelligently. A Gas chromatograph should be installed for a group of wells which would monitor the produced fluid composition on a regular basis. The intelligent software would compare the simulated compositions at the surface( taking into account condensate fallback in well if any) vs actual compositions from the GC. If the deviation crosses a prescribed limit the well should be re-simulated using the present composition and bottomhole pressure data. These new simulation data can be re-fed into the system and the flow rate could be controlled to attain minimum deviations from the simulations. This would minimize condensate deposition in the reservoir.
Microbial action can be used at later stages of production.When considerable condensates are deposited in the reservoir, microbes can be introduced into the reservoir along with nutrients. These microbes will be special microbes which will break the heavier hydrocarbons in the condensates and produce light gases like ethane, propane etc. This can reduce the need for gas cycling in reservoirs where the condensate content is low due to which gas cycling is rendered unecomonical.This will also reduce the limitations of residual saturation, around 20% in most reservoirs, since the condensates would be broken up into lighter hydrocarbons.
Gas condensate reservoirs with a low condensate content,pressures near the dew point and temperatures between critical point and cricondentherm would be an ideal candidate for the mentioned techniques.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012