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Abstract: Pande Gas Field - Integrated Upstream/Downstream Remote Exploitation Gas Project

Abdula, Issufo - Empresa Nacional de Hidrocarbonetos de Mozambique and Nelson, Dennis A.* and Reese, Cheryl L. - Enron Oil & Gas International

This integrated project encompasses the development of Pande Field, building production and gathering facilities, the design and construction of a 600 kilometers gas pipeline to Maputo, and design and construction of a direct reduced iron and steel plant - Fig. 1. The Pande Gas Field is a unique combination structural-stratigraphic geological feature. The field is located onshore 20 kilometers from the coast in the province of Inhambane approximately 600 kilometers to the northeast of Maputo, Mozambique. The concession area totals 26,000 square kilometers (6,422,000 acres). The onshore portion is 22,000 square kilometers (5,434,000 acres), and the offshore area is 4,000 square kilometers (988,000 acres) - Fig. 2.The field was discovered in late 1961 by the Pande-1 wildcat operated by the Mozambique Gulf Oil Company. After the successful results of the discovery well, five more wells were drilled to appraise the productive horizons of the Cretaceous Grudju Formation. The Pande-4 well located 3 kilometers north-northeast of the Pande-1 blew out on 29 October 1965 as the drill string was coming out of the hole in preparation for running additional pressure tests. A large crater formed approximately 900 meters from the wellhead with a diameter of 350-400 meters and a depth of 12-15 meters. The well was successfully brought under control by the fourth relief well Pande-4D on 2 August 1967 -after blowing uncontrolled for 459 days. The remaining wells were drilled from 1967 to 1996 three companies: 2 by Gulf, 6 by Tymengeologia of Russia, and 3 by ENH and the World Bank. To date, a total of over 2,000 kilometers of seismic data have been acquired over the Pande area to further establish the ultimate producibility of the Pande gas accumulation. A total of fifteen wells have been drilled on this accumulation, only the Pande-3 and Midjige-1 being unsuccessful due to the lateral facies changes of the Lower Grudja formation to a siltstone. The G-6 Sand contains the bulk of the remaining reserves which were partially depleted by the Pande-4 blowout.

The Late Cretaceous Sandstones of the Lower Grudja Formation were formed depositionally in nearshore shallow marine environment with internal shale horizons forming top, lateral & basal seals. Hydrocarbon migration combined to trap a significant accumulation of hydrocarbon gas with migration originating from east to west to the Pande area. Excellent lateral continuity appears to exist across the area until depositional conditions cause a facies change to the North, South, and West creating a fine grained siltstone (permeability barrier) which helped trap hydrocarbons. The primary gas bearing horizon is the G-6 Sand which is approximately 20 meters in gross thickness at its thickest point in the center of the field. The G-6 Horizon is divisible into two sand bodies the G-6 Upper Sand and G-6 Lower Sand, which are separated by an unconform-ity. The G-6 Upper Sand's porosities range from 23-33%, water saturation's 27-50%, and permeabilities from up to 4 darcies. The sandstone is a medium to coarse-grained quartzose, with glauconite. The G-6 Lower Sand is fine-grained sandstone with clay content that increases with depth. Petrophysical and core analysis have shown porosities of 27-28%, water saturation's 50-80%, and gas permeabilities of less than 60 milli-darcies. Wire-line, cores, and drill-stem testing show excellent producibility to be possible in this sand.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil