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Total, operating on behalf of Shell, ExxonMobil and Dana, is developing the Otter field in the North Sea. The development plan calls for three horizontal producers and two water injectors. Their location is critical to optimize production and reserves in this complexly faulted reservoir. The first well started producing in October 2002. The reservoir model assumed fault transmissibility and predicted that there would be a small but measurable depletion by the time the third well was drilled. When this well was entering the reservoir in January 2003, it was important to determine whether the reservoir drawdown matched the reservoir model. Formation pressure information was required as soon as possible, as this would have implications on the onward drilling program of well three and possibly on the relocation of one of the injectors. Since this well was penetrating the reservoir section sub-horizontally, any wireline formation tester would have to be run on drill pipe. An innovative technology, the Drilling Formation Tester (DFT), was utilized to gather the formation pressure data. The DFT is a Logging While Drilling Tool (LWD) that performs formation pressure test using a dual packer configuration, a downhole pump, and a quartz gauge. It uses mud-pulse telemetry to transmit the downhole formation pressure data to the surface in real-time. Multiple tests can be performed to measure formation pressure and establish the formation fluid gradient. A Formation Evaluation LWD suite was run with the DFT. This allowed geosteering of the well into the optimal part of the reservoir and to investigate the reservoir pressure regime while drilling. This combination of LWD tools facilitated while drilling a comprehensive understanding of the reservoir, its fault compartments and pressure regime. The real-time pressure data indicated that the well was located in a high permeability layer, confirmed the reservoir pressure model and facilitated the real-time decision-making process. The use of an LWD formation pressure tester was economic by saving an extra trip in the hole that would be required to acquire drill pipe conveyed wireline pressure data. It both added value through reduced operational risks as well as saving direct and indirect formation evaluation costs. |
