The major tasks of production geology is to ensure that the newly discovered reservoir is developed and produced in an optimum way. This requires the determination of the gross bulk volume of the reservoir, lithology distributions, structure and petrophysical properties. The results are represented by maps (structure, thickness, porosity), cross sections and 3D models. In cooperation with reservoir engineers, a field development plan is made. Appraisal wells are used to determine the extent of the oil or gas field. Production wells are used to recover the hydrocarbons from the reservoir.
An even more detailed reservoir model is needed to establish and successfully operate a subsurface gas storage project. Gas is reinjected into depleted reservoirs using horizontal wells (up to several kilometres long) when demand is low. It can be withdrawn later when needed.