6. Intangible assets

The following table summarizes the components of our finite-lived intangible assets as of September 30, 2022, and December 31, 2021:

Intangible assets are amortized over the period the Company expects the asset to generate cash flows. As such, we amortize each electric frac license through the remaining license period, beginning when the initial fleet built under each license is placed into service, a period we estimate to be 17 years. For technology acquired during 2021, we estimated this period to be seven years. For technology acquired in 2022 related to the acquisition of FTSI, we estimated the period to be three years. Amortization expense related to intangible assets was $0.7 million and $0.2 million for the three months ended September 30, 2022 and 2021, respectively. Amortization expense related to intangible assets was $1.4 million and $0.5 million for the nine months ended September 30, 2022 and 2021, respectively.