Property and equipment consisted of the following at December 31, 2021 and 2020 (in thousands):


	2021			2020
Equipment	$	7,742,101		$	7,647,451
Oil and natural gas properties		229,403			222,738
Buildings		182,280			193,503
Land		24,562			25,781
Total property and equipment		8,178,346			8,089,473
Less accumulated depreciation, depletion, amortization and impairment		(5,846,591	)		(5,328,432	)
Property and equipment, net	$	2,331,755		$	2,761,041

Depreciation, depletion, amortization and impairment — The following table summarizes depreciation, depletion, amortization and impairment expense related to property and equipment, intangible assets and liabilities for 2021, 2020 and 2019 (in thousands):


	2021		2020		2019
Depreciation and impairment expense	$	818,999	$	644,943	$	974,206
Amortization expense		24,606		19,281		17,722
Depletion expense		5,573		6,686		11,945
Total	$	849,178	$	670,910	$	1,003,873

On a periodic basis, we evaluate our fleet of drilling rigs for marketability based on the condition of inactive rigs, expenditures that would be necessary to bring inactive rigs to working condition and the expected demand for drilling services by rig type. The components comprising rigs that will no longer be marketed are evaluated, and those components with continuing utility to our other marketed rigs are transferred to other rigs or to our yards to be used as spare equipment. The remaining components of these rigs are abandoned. In the fourth quarter of 2021, we identified 43 legacy non-super-spec rigs and equipment to be abandoned. Based on the strong customer preference across the industry for super-spec drilling rigs, we believed the 43 rigs that were abandoned had limited commercial opportunity. We recorded a $220 million charge related to this abandonment in the fourth quarter of 2021. In the second quarter of 2020, we recorded an impairment of $8.3 million related to the closing of our Canadian drilling operations. In 2019, we identified 36 legacy non-APEX® rigs and related equipment that were abandoned. Based on the strong customer preference across the industry for super-spec drilling rigs, we believed the 36 rigs that were abandoned had limited commercial opportunity. We recorded a $173 million charge related to this abandonment.

We also periodically evaluate our pressure pumping assets for marketability based on the condition of inactive equipment, expenditures that would be necessary to bring the equipment to working condition and the expected demand for such equipment. The components of equipment that will no longer be marketed are evaluated, and those components with continuing utility will be used as parts to support active equipment. The remaining components of this equipment are abandoned. In the fourth quarter of 2021, we recorded a charge of $32.2 million related to the abandonment of approximately 0.2 million horsepower within our pressure pumping fleet. The majority of these units were frac pumps but also included pump down units. These units were abandoned due to changes in customer preferences for dual fuel, advancements in technology, and prohibitive reactivation costs. In 2019, we recorded a charge of $20.5 million for the write-down of pressure pumping equipment. There was no similar charge in 2020.

We also periodically evaluate our directional drilling assets. In the fourth quarter of 2021, we abandoned certain directional drilling equipment totaling $2.5 million and recorded a charge on our developed technology intangible asset of $11.4 million due to advances in technology that rendered those assets, and their related spare parts inventory, obsolete. During 2019, we recorded a charge of $8.4 million for the write-down of directional drilling equipment. There was no similar charge in 2020.

We review our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying amounts of certain assets may not be recovered over their estimated remaining useful lives (“triggering events”). In connection with this review, assets are grouped at the lowest level at which identifiable cash flows are largely independent of other asset groupings. We estimate future cash flows over the life of the respective assets or asset groupings in our assessment of impairment. These estimates of cash flows are based on historical cyclical trends in the industry as well as our expectations regarding the continuation of these trends in the future. Provisions for asset impairment are charged against income when estimated future cash flows, on an undiscounted basis, are less than the asset’s net book value. Any provision for impairment is measured at fair value.

Based on current commodity prices, our results of operations for the year ended December 31, 2021 and management’s expectations of operating results in future periods, we concluded that no triggering events occurred during the year ended December 31, 2021 with respect to our asset groups within our operating segments. Our expectations of future operating results were based on the assumption that activity levels in all of our reporting segments and our other operations will remain relatively stable or improve in response to relatively stable or increasing oil prices.

Due to the decline in the market price of our common stock and commodity prices in the first quarter of 2020, we lowered our expectations with respect to future activity levels in certain of our operating segments. We deemed it necessary to assess the recoverability of our contract drilling, pressure pumping, directional drilling and oilfield rentals asset groups as of March 31, 2020. We performed an analysis as required by ASC 360-10-35 to assess the recoverability of the asset groups within our contract drilling, pressure pumping, directional drilling and oilfield rentals operating segments as of March 31, 2020. With respect to these asset groups, future cash flows were estimated over the expected remaining life of the assets, and we determined that, on an undiscounted basis, expected cash flows exceeded the carrying value of the asset groups, and no impairment was indicated. Expected cash flows, on an undiscounted basis, exceeded the carrying values of the asset groups within the contract drilling, pressure pumping, directional drilling and oilfield rentals operating segments by approximately 15%, 22%, 3% and 9%, respectively.

For the assessment performed in the first quarter of 2020, the expected cash flows for our asset groups included revenue and operating expense growth rates. Also, the expected cash flows for the contract drilling, pressure pumping, directional drilling and oilfield rentals asset groups were based on the assumption that activity levels in all four segments would generally be lower than levels experienced in the second half of 2019 and the first quarter of 2020 and would begin to recover in 2022 in response to improved oil prices.

After the assessment we performed in the first quarter of 2020, we concluded that no triggering events occurred during the periods thereafter through December 31, 2020 with respect to our asset groups based on the recent results of operations leading up to that date, management’s expectations of operating results in future periods and the prevailing commodity prices at the time.

Due to the decline in the market price of our common stock and commodity prices, our results of operations for the quarter ended September 30, 2019 and management’s expectations of operating results in future periods, we lowered our expectations with respect to future activity levels in certain of our operating segments. We deemed it necessary to assess the recoverability of our contract drilling, pressure pumping, directional drilling and oilfield rentals asset groups as of September 30, 2019. We performed an analysis as required by ASC 360-10-35 to assess the recoverability of the asset groups within our contract drilling, pressure pumping, directional drilling and oilfield rentals operating segments as of September 30, 2019. With respect to these asset groups, future cash flows were estimated over the expected remaining life of the assets, and we determined that, on an undiscounted basis, expected cash flows exceeded the carrying value of the asset groups, and no impairment was indicated. Expected cash flows, on an undiscounted basis, exceeded the carrying values of the asset groups within the contract drilling, pressure pumping, directional drilling and oilfield rentals operating segments by approximately 35%, 54%, 23% and 7%, respectively.

For the assessment performed in 2019, the expected cash flows for our asset groups included revenue and operating expense growth rates. Also, the expected cash flows for the contract drilling, pressure pumping, directional drilling and oilfield rentals asset groups were based on the assumption that activity levels in all four segments would generally be lower than levels experienced in 2019 and would begin to recover in late 2020 or 2021 in response to improved oil prices.

We concluded that no triggering events occurred during the quarter ended December 31, 2019 with respect to our asset groups based on the recent results of operations leading up to that date, management’s expectations of operating results in future periods and the prevailing commodity prices at the time.