Production operations in a modern oilfield production system becomes gradually more complex as the water cut increases and artificial lift is applied. To ensure production is continuously optimized, closer communication and a positive feedback loop are required between the petroleum engineer, the production supervisor and control room operators. ADNOC is developing a series of decision support systems to improve collaboration in production operations. One of the key systems consists of 2D operating envelopes charts for the gas lift wells, which relate the control variables of the wells, gas lift rate and production choke opening, with the expected flow behavior. The operating envelopes are visible in the control room and provide guidance to the operators on the stable production range of the wells, whilst leaving flexibility for adjustments, as the immediate production context evolves throughout the day.
The operating envelopes were computed by performing sensitivities on choke and gas lift settings on nodal analysis models of wells, chokes and flowlines, with different manifold pressures. The calculated rates and pressures are compared with a series of mechanical, reservoir and production constraints, to build the 2D envelope chart. The envelope shows the region where the well is in a stable and safe region, together with regions exceeding the maximum allowed casing pressure (MAWOP), hydrate formation, flowing below bubble point, exceeding allowed rates, tubing + flowline erosion, casing heading and tubing heading. The current operating point is shown in the chart, together with the recommended optimum setpoints.
Production operations use the system as a guidance tool to control the wells. The petroleum engineer is expected to keep the well models up to date, to make the operating envelopes robust. On the other hand, the operators are expected to test the wells frequently, to ensure the good quality of the models. Around 2-5% of oil production increase is expected from the continued use of this framework.