Abstract

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.

Introduction

When reservoir pressure around a well in a gas condensate reservoir drops below the dew point pressure, retrograde condensation occurs and three or four regions with different condensate saturations are created around the well. The outermost region has initial gas saturation. The next region towards the well has an immobile condensate saturation which is below critical saturation. The third region has condensate saturation above critical saturation and therefore both condensate and gas are flowing. In some wells there may exist a fourth region in immediate viscinity of the wellbore due to high capillary number and velocity stripping effects where the condensate saturation is slightly lower and hence the gas relative permeability is higher than that in the third zone. Gringarten et al 1,2 showed that these different regions appear as different permeability zones in well tests, when the analysis is made using single phase or dry gas pseudopressure function.

The paper presents the analysis for several unstimulated and stimulated gas condensate well tests from Raageshwari Deep reservoir using single phase pseudopressure function.

The Reservoir

Raageshwari Deep gas field was discovered in 2003. The field is situated at the northern end of the Central Basin High - a 40km long composite feature of elevated N-S oriented fault terraces, arranged en echelon within the Southern Barmer Basin, Rajasthan, India.

During 2004–2006 the field underwent appraisal, with the drilling of five additional wells, namely Raageshwari-4, 4Z, 5, 6 and 7. Being close to the gas water contact, Raageshwari-6 did not produce gas from the deep reservoirs. Well test analysis carried out for Raageshwari-4, 4z, 5 and 7 are discussed in this paper.

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