but the variation probably is not significant. However, for the typical reservoir, the rate at which helium is removed can significantly affect how much helium remains when gas flow drops below levels at which it no longer is profitable to remove more gas. Typically, the structure of reservoirs is such that the greater the initial rate of production, the more gas remains when that unprofitability level is reached.

Gas fields do not generally consist of a single well. Instead, there are a number of wells within a producing field. The spacing of the wells will depend on the characteristics of the field. Highly permeable reservoir rock (all else equal) may not require as great a density of wells as less permeable reservoirs because fluids can flow more easily through the high-permeability reservoir and so can travel further to a well for production. Multiple wells can complicate production. Not only is an individual well impacted by the production choice for that well, but its production potential is also affected to the extent that production from other wells impacts pressure in its vicinity.

The production path chosen can also impact future potential by degrading the reservoir characteristics (usually under drawdown strategies that rely on higher pressure) and by changing the gas properties as fluids from the surrounding area move into the reservoir, commingling with the gas in place. Finally, production potential can be impacted by the addition of compression in the field, which impacts the pressure of the field and the field’s future potential.

With these concepts in mind, various production strategies for Bush Dome Reservoir can be considered. Bush Dome Reservoir is slightly different because it is not a new field being considering for initial production. Rather, it has already been produced, and that production history impacts its current and future production capabilities, constraining the latter. However, the concepts presented in the preceding example apply at any point during the producing life of a field. In the end, determining the optimal production path depends on the objective of the producer.

MAXIMIZE WITHDRAWALS THROUGH 2015

Maximizing withdrawals is an objective that relates only to the physical resource and does not consider the costs of withdrawals relative to the value of the helium. To maximize withdrawals over a given time horizon, the production plan would have to take into account the field characteristics. Given that reservoir pressure declines with production, this objective would result in declining production over the time horizon. The initial production rates would be chosen to maximize the production potential of the pressure gradients in the reservoir over the time horizon, while considering the potential for reservoir degradation. This objective could include (or not) added compression and/or new wells.

The terminal time of 2015 adds a restriction to this production objective. Depending on the reservoir characteristics, a longer (or shorter) time horizon



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