Shale gas is an increasingly booming resource and it has been predicted to increase from 1% in 2000 to 40% in 2035 of the total US domestic gas produced. Since shale gas is both industrially economical and environmentally clean compared to oil or coal as a resource, many studies are focused on developing technologies to monetize shale gas. However, one of the key challenges in utilizing shale gas is its fluctuating flow rate and compositional behavior. The flow rate of a shale gas well dwindles over a period of time and the composition of shale gas differs from well to well in the same shale play. This provides a challenge in designing a plant of optimum size for a shale gas processing and NGL recovery plant.
In this study, this uncertainty in shale gas feed flow rate and composition is addressed while designing a shale gas processing and NGL recovery plant. First, different shale gas flow rates are chosen over a period of shale gas well life based on the average shale gas rate declination curve of a shale play. Second, two different process flow sheets are developed (i) using conventional technology and (ii) using novel technology. In the novel technology, the NGL recovery section of the conventional technology is modified to accommodate novel changes such as using a divided wall column or pre-fractionated sequence to separate methane, ethane, and propane. Later, these process flow sheets are simulated in Aspen plus for comparing the economics of different plant sizes. Furthermore, heat integration and optimization of individual units of the process flow sheets are carried out using pinch and sensitivity analyses, respectively. Lastly, the economic analysis of a plant of optimum size with constant feed flow rate over its plant life is evaluated. In this case, shale gas from different wells is collected in a header and adjusted such that the shale gas flow rate is constant to the plant. Environmental impact of the process is also observed.
From the economic analysis of various cases for conventional and novel technology, it is observed that case-3 provides the optimum plant design with highest ROI percentage compared to other cases and for case-3, novel technology ROI is 4.17% more compared to conventional technology. Finally, constant production rate case, at the flow rate of case-3, the ROI percentage is observed to be more than minimum requirement implying that this processing plant is economically viable to implement.
