Performance of Seeligson Zone 20-B Enriched Gas-Drive Project

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Abstract
An enriched gas-drive project was initiated in Zone 20-B, Seeligson field, Jim Wells and Kleberg counties, Tex., on March 19, 1957. To date nearly 2.5 billion cu ft of an enriched gas mixture composed of about 50 per cent methane and 50 per cent propane has been injected through two injection wells. There are 11 producing wells in this project. Cumulative production since injection began is approximately 750,000 bbl of stock-tank oil, and the current oil-producing rate for the reservoir is 1,000 bbl per calendar day. Enriched gas in appreciable quantities has reached the first row of producing wells down-structure of the two injection wells. As predicted from laboratory work, displacement of reservoir oil by the enriched gas mixture has proved to be highly efficient. Project results to date are encouraging, and additional information should be gained from a conformance evaluation workover to be performed in the near future. The project is still at an early stage of operation because the enriched gas volume injected to date is only 16 per cent of the hydrocarbon pore volume. Introduction: The enriched gas-drive process entails the injection of a gas which has been enriched through the addition of such intermediate hydrocarbon components as ethane and propane to the extent that it is completely soluble in the oil to be displaced. Enriching components in the gas are absorbed into the oil, forming a bank of swelled oil that is miscible with the oil ahead and the gas behind. There is no sharp interface between the displaced and displacing fluids; rather, there is a zone of short duration between the injected and resident fluids in which the fluid properties grade from those of the displaced to the displacing medium. Under these conditions, capillary and interfacial tension forces are not believed to be present. High recovery is made possible by removing or reducing the interfacial tension between the injected material and the reservoir oil to the extent that essentially no oil is left as residual droplets.

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