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Appraisal and delineation wells are wells with at least one objective of gaining data to improve the understanding of the reservoir. During this phase of the life-cycle, a rig schedule is typically developed with input from most Asset Team members, but most notably the drilling engineer(s), the development geologist(s), and the reservoir engineer(s). The rig schedule prioritizes the wells to be drilled based on the objectives of the well and the logistics of the well (availability of off-the-shelf equipment and the need for long lead time equipment).
During the appraisal and delineation period, the drilling engineers continue to work with the development geologists to create the drilling proposals. During this phase of the life-cycle, the rig schedule is heavily weighted with drilling activity; however, Plugging and Abandoning (P&A) and Temporary Well Suspension (mothballing the wells for future use as development wells) activities are also included.
During this period, a learning curve for drilling the wells is formed, as the geologic formations to be drilled through and the Drilling Penetration Rates through these formations become understood. Often, this learning curve is applied to the Development Plan and economics of the field or reservoir.
If multiple drilling rigs are available for the project, then the different appraisal and delineation wells in the rig schedule are prioritized and assigned. On the other hand, if a single rig or several rigs are servicing multiple projects, then gaps in the rig schedule are assigned to a project to allow for the timely interpretation of data from a well, so that future wells and well proposals can benefit from that data.