Developing a Discovery
When promising amounts of oil and gas are found in an exploratory well, a programme of detailed field appraisal may begin. The size of the field must be established, and the most efficient production method worked out in order to assess whether it will repay, with profit, the huge costs of offshore development and day-to-day operation. Appraisal may take several years to complete and is itself very costly.
Appraisal draws together information from all available techniques. Detailed seismic surveys build up an accurate 3-dimensional image of the discovery, and appraisal wells are drilled to confirm the size and structure of the field (F75). Wireline logging in each new well yields data on porosity and fluid saturation and the thickness of the hydrocarbon-bearing rocks, while production testing yields hydrocarbon samples and information on reservoir productivity, temperatures and pressures. Oil, gas and reservoir rock samples are analysed in the laboratory. Most fields have both good and bad features which must be fully considered when deciding whether to develop.
