From exploration to development, the challenges of cost-effective exploitation of hydrocarbon reservoirs are enormous and diverse. A lack of detailed understanding of the petrophysical building blocks of the reservoir in the early stages of its development usually constitutes a major impediment to achieving an efficient development strategy. In addition, stratigraphic and structural uncertainties exist and are only minimised as more wells are drilled to develop the reservoir. The hydrocarbon fluid types, accumulation, and stratification can also present complex uncertainties in identification and quantification, depending on the depositional environment of the reservoir.
The EE reservoir is structurally a rollover anticline with shallow marine deposits. It was discovered in 1965 and was put on stream in 1970. The reservoir has had 12 drainage completions to date, 7 of which currently flow with a total daily production of 7,100 BOPD. Until 1998, completion and development had been based on conventional data acquired at various time since the reservoir was discovered.
In 1998, a new nuclear magnetic resonance (NMR) logging device was run in the reservoir for the first time. Logs were acquired in well XT, which penetrates the southeastern flank of the reservoir. The results provided an improved definition of fluid flow units in the reservoir. The effective porosity was found to average between 32 and 34% with less than 2% variation across the reservoir. However, the bulk volume irreducible (BVI) showed considerable variation with depth across the reservoir, defining an egg-shaped flow-unit body. Permeability was on the order of 1.0 darcy, while the clay spectrum indicated laminated interbedded shales with clean sandstone layers cutting across the upper section of the reservoir. Core data from a nearby well was integrated with the NMR results, and a good correlation was obtained. Implications of these data on future completions and reservoir drainage strategy are highlighted in the paper.