The purpose is to create a rolling production forecast, with a range of scenarios to cover uncertainties, such as total gas supply. There are three key challenges:
- data management
- non-linear optimisation
- communication of results to team members.
To maximize the total oil production, the constrained supply of injection gas for gas-lift has to be allocated optimally across many wells. The forecast results are charted for comparison with actual historical production, both for totals and for individual wells.
For each oil well, DynamicForecaster uses pre-calculated Gas-Lift Performance Curves (GLPC) for each well, which change over time as the reservoir pressure declines. Usually, the optimal gas injection rate for a well is in the range 40-60% of the gas rate for its peak oil rate, for reasons of flow stability and economics.
An optimization procedure was presented by Robert N. Hatton and Ken Potter, 2011 “Optimization of Gas-Injected Oil Wells” SAIC, Huntsville, AL, U.S., SAS Global Forum 2011, Paper 195-2011, including a set of gas-lift performance curves for 100 wells. Surprisingly, they presented results only for unbounded optimizations (i.e. which do not comply with the 40-60% range for every well).
DynamicForecaster is able to compute the bounded optimization for these 100 wells, as shown in the pair of charts below:
References for gas-lift optimization (opens in a new page)