Nodal and least-cost analysis on the optimization of natural gas production system constraints to extend the plateau rate of a conceptual gas field

Abstract

The supply of natural gas in any country is determined by energy demand. Furthermore, supply agreements specify that gas should be supplied at a constant rate for a specified period. However, due to the decline in reservoir pressure as gas fields continue to produce, high constant rate production is usually uncertain, and the plateau may not reach the agreed-upon period. Therefore, this study was conducted to optimize gas production system constraints and extend the production plateau rate of a conceptual dry gas field. The field was made up of the sand packages CF2 upper, CF2 lower, CF1 upper, and CF1 lower. A total of 1316.9 Bscf were assumed to be the estimated gas field reserves, and 423.3 Bcf were assumed to be the remaining economically recoverable gross 2 P sales of natural gas. The field also contained natural gas at the Miocene and five production wells, numbered PW-1, PW-2, PW-3, PW-4, and PW-5. The field's estimated average constant gas production rate as of July 2021 was 85 MMscfd. The field's gas demand was forecasted in three phases, with the third beginning on November 1, 2019, at a rate of 130 MMscfd. After applying Nodal Analysis with the help of Integrated Production Modelling (IPM) and Least Cost Analysis methods, the study found that the gas production plateau of that field started to decline on March 1, 2017, after 1 year and 5 months of production when constrained to 130 MMscfd. However, after modifying the constraints to match various assumed production histories, it was discovered that the plateau would start to decline on June 1, 2023, after 8 years of production. Therefore, eight possible combinations of varying the three production constraints were developed and simulated to examine their effect on extending the field production plateau. These constraints were separator pressure, tubing size, and the number of layers perforated. The best combination was to lower the separator pressure to 725 psia, increase the tubing size to 4 inches, and perforate three more zones (zones I, C, and D). This was the only combination that appeared to extend the production plateau for 8 years until October 1, 2031, as required in the 16 years gas sales agreement (GSA). This approach was economically compared to the options of using a compressor and drilling future wells, and it was found to be 34.05% cheaper than the compressor usage option and 98.25% cheaper than drilling a well. As a result, the operators of this conceptual gas field are advised to adopt this approach to extend the field's plateau.