Early Performance and Planning for a Simultaneous Thermal Enhanced Oil Recovery Project and Sulfur Mining Operation at Main Pass 299

Abstract

SPE Members Abstract This paper will review the early production performance, development planning, and reservoir simulation prediction for a unique thermal enhanced oil recovery project and sulphur mining operation in a recently discovered reservoir at Main Pass 299. In this field, a relatively large accumulation of oil (approximately 100 million barrels in-place) is contained within a complex structure of sandstone, carbonate, and sulphur bearing formations lying directly above a shallow piercement salt dome at depths ranging from 1200 to 1532 feet subsea. The sulphur-bearing formation has the largest sulphur reserves (67 million tons) of any mine in North America and is one of the largest mines in the world. As part of the sulphur mining operation, 240,000 barrels per day of 325 degrees F water will be injected into the formation. Much of this water will contact and heat up the oil, significantly reducing the oil viscosity and greatly enhancing the ultimate oil recovery. Main Pass 299 is located about 90 miles southeast of New Orleans in 220 feet of water (Figure 1). Introduction The Main Pass 299 oil development is unique in many ways. Produced crude is relatively heavy and sour, with a gravity of 22 degrees API and a H2S content of 14.9 mole % in the solution gas and 2.5% in the gas cap gas. Gas processing requires usage of the only offshore Claus unit installation in the Gulf of Mexico for removal of sulphur from sour gas, The productive formations were originally underpressured with a pressure gradient of only 7.1 PPG (0.37 psi/ft). Currently, electric submersible pumps are being utilized to lift the crude to the surface. Eleven of the eighteen development wells are drilled horizontally in order to minimize anticipated problems from water and gas coning. The vugular carbonate formation is extremely productive, having been tested at rates up to 7500 BOPD with calculated permeabilities of at least 18 darcies. Total platform capacity has tested as high as 59,000 BOPD. A three-dimensional, three-phase, thermal reservoir simulation model of the total field with 9744 grid blocks has been built as a tool to help optimize both oil and sulphur production operations. Simulation is needed to properly understand fluid flow, heat transfer, and the overall effect of hot water injection on oil recovery. The additional heat introduced by the sulphur mining operations is estimated to increase recoverable oil reserves by 17.6 million barrels, with total recoverable oil estimated at 39.2 million barrels. Primary recovery mechanisms are by gas cap expansion and solution gas drive aided by gravity segregation. No natural water drive is expected due to the very small aquifer. Secondary recovery is by hot water injection during sulphur mining operations. Geology and Exploration The geologic structure of Main Pass 299 is determined by an extremely shallow piercement salt dome rising to less than 2000 feet of sea level. The location and structural form of the dome have been generally understood since the early 1960s when oil production was initiated from other productive zones on the periphery of the dome. To date more than 57 million barrels of oil have been produced from these zones. In 1988, the Federal Government carried out a lease sale for offshore exploration and production of sulphur. As a result of this sale, 20 sulphur exploration wells were drilled on top of the dome in late 1988 and early 1989, and a very large accumulation of sulphur was discovered. In addition, a significant accumulation of oil was also found. P. 35^