Appraisal wells are to determine flow rates and economic feasibility.
When exploratory drilling is successful, more wells are drilled to determine the size and the extent of the field. Wells drilled to quantify the hydrocarbon reserves found are called ‘outstep’ or ‘appraisal’ wells.
The appraisal stage aims to evaluate the size and nature of the reservoir, to determine the number of confirming or appraisal wells required, and whether any further seismic work is necessary.
The technical procedures in appraisal drilling are the same as those employed for explo- ration wells.......... A number of wells may be drilled from a single site, which increases the time during which the site is occupied.
Deviated or directional drilling at an angle from a site adjacent to the original discovery bore- hole may be used to appraise other parts of the reservoir, in order to reduce the land used or ‘foot print’. -----