Miscible Drive Field Applications in the Bisti Pool

Introduction The Bisti Lower Gallup oil pool, San Juan County, New Mexico, covers approximately 24,000 acres, is 24 miles long and 1.5 miles wide. The oil productive Lower Gallup formation is of Upper Cretaceous age, and is composed of alternating layers of sandstone, sandy shale, and shale. The reservoir is encountered at a depth of 4,900 ft and has an average gross thickness of 135 ft of which only 10 to 20 per cent will have a permeability greater than 1 md. The best developed sand follows the crest of the long, narrow sand bar. An LPG miscible displacement pilot project was started in Aug., 1957, on a 40-acre five-spot in the upper zone of the Lower Gallup. In the pilot area the upper (producing) zone is a light grey, medium-grained, clean, well sorted sandstone with a porosity of 13 per cent, permeability of 100 md, and net pay thickness of 16 ft. The permeability varies from 400 to less than 1 md. The stock-tank oil has a gravity of 38° API. Measured fluid properties at the bubble point pressure of 1,207 psia and reservoir temperature of 145°F are solution gas-oil ratio, 407 cu ft/bbl; formation volume factor, 1.26; oil viscosity, 0.7 cp; and gas viscosity, 0.015 cp. The flood is conducted at reservoir pressures slightly in excess of the bubble point pressure. History of the Pilot Early performance predictions indicated that the field primary recovery would be low because the reservoir is thin and tight, and operating under a solution gas-drive mechanism. The gas-driven LPG miscible displacement pilot project was recommended after studies of high pressure vaporizing gas drive did not indicate great benefits. The pilot consists of four producing wells spaced 40 acres apart with an injection well completed in the center of the four producers. The four pilot wells are the Sunray Mid-Continent Federal C wells No.1 and 2, British-American Marye No.1 and Phillips Hospah A No.1. Also participating in the project are EI Paso Natural Gas Products Co., Amerada Petroleum Corp. and Shell Oil Co., although they are not operating wells in the pilot area.