As E&P budgets tighten and cash flow becomes the ultimate goal, producers are seeking ways to reduce costs and increase production. Mature wells, which still have significant reserves but their best producing days are behind them, are particular targets for evaluation because their margins are smaller than those of new wells.
The main focus in well evaluation is the lift system. Proper choice, design and management of this component trumps all other issues in determining production and profitability of a mature well.
Most wells start with high production rates between 1,000 and 3,500 bbl/d. Depending on the well and its gas-liquid ratio, electric submersible pump (ESP) or continuous gas lift are the most common choices. As production drops below 350 bbl/d, those high production systems are no longer efficient, and ESPs may even be damaged by working with inadequate flow.
When changing lift systems, companies choose between high-capital-expense rod pump and lower cost alternatives such as gas-assisted plunger lift (GAPL) and intermittent gas lift (IGL).