Well Test Analysis in a Lean Gas Condensate Reservoir

摘要

The Raageshwari Deep Gas Field, situated at the northern end of the Central Basin High within the onshore RJ-ON-90/1 Contract Area, Rajasthan State, India, was discovered in 2003. It is a tight lean gas condensate volcanics reservoir, with excellent gas quality of 80% methane and low CO2 and no H2S content. Since discovery, several appraisal wells have been drilled in the field and tested extensively. The wells have produced gas rates in the range of 2-4 MMscf/d with condensate gas production ratios in the range of 40-50 STB/MMscf. The drawdowns during the production tests have been high, in the range of 3000-4000 psi, indicating the very low permeabilities of the reservoir. This paper describes the tight volcanic reservoir, the reservoir fluid present in it and the well test analysis results from several wells drilled in the field. The reservoir being very tight, the well tests have been carried out for long time periods, extending beyond a month, to enable deriving of meaningful information. As during testing the pressure drops below the dew point in areas around the wellbore, condensate dropout is expected to occur, influencing the relative permeabilities for gas and condensate flow. Radial composite models have been found to allow reasonable matching of observed test behaviour. Several hydrofracturing jobs have been carried out in these wells. Well tests carried out after completion of hydro-frac jobs have also been analysed and presented.