PROPERTIES AND EQUIPMENT

The following table presents the components of properties and equipment, net of accumulated depreciation, depletion, and amortization ("DD&A"):



	March 31, 2018			December 31, 2017
	(in thousands)
Properties and equipment, net:
Crude oil and natural gas properties
Proved	$	4,706,258		$	4,356,922
Unproved	1,055,774			1,097,317
Total crude oil and natural gas properties	5,762,032			5,454,239
Infrastructure, pipeline, and other	125,529			109,359
Land and buildings	12,679			10,960
Construction in progress	294,311			196,024
Properties and equipment, at cost	6,194,551			5,770,582
Accumulated DD&A	(1,963,294		)	(1,837,115		)
Properties and equipment, net	$	4,231,257		$	3,933,467

The following table presents impairment charges recorded for crude oil and natural gas properties:



	Three Months Ended March 31,
	2018		2017
	(in thousands)

Impairment of proved and unproved properties	$	33,130	$	2,102
Amortization of individually insignificant unproved properties	58		91
Impairment of crude oil and natural gas properties	$	33,188	$	2,193

During the three months ended March 31, 2018, we recorded impairment charges of $26.9 million, primarily related to certain unproved Delaware Basin leasehold positions that expired during the three months ended March 31, 2018.

Additionally, we corrected an error in our calculation of the unproved properties and goodwill impairment originally reported in the quarter ended September 30, 2017. The correction of the error resulted in an additional impairment charge of $6.3 million, recorded in the three months ended March 31, 2018, which we have included in the impairment of properties and equipment expense line in our condensed consolidated statement of operations. We evaluated the error under the guidance of Accounting Standards Codification 250, Accounting Changes and Error Corrections ("ASC 250"). Based on the guidance in ASC 250, we determined that the impact of the error did not have a material impact to our previously-issued financial statements or those of the period of correction.

Utica Shale Divestiture. In March 2018, we completed the sale of our Utica Shale properties (the "Utica Shale Divestiture") for net cash proceeds of approximately $39.0 million, subject to certain customary post-closing adjustments. We recorded a loss on sale of properties and equipment of $1.4 million for the three months ended March 31, 2018. The divestiture of the Utica Shale properties did not represent a strategic shift in our operations or have a significant impact on our operations or financial results; therefore, we did not account for it as a discontinued operation.

Classification of Assets as Held-for-Sale. Assets held-for-sale as of March 31, 2018 were $1.6 million for a field office facility. We subsequently sold the field office facility in April 2018 for $1.9 million and will record a gain on sale of properties and equipment of $0.3 million during the second quarter of 2018. Assets held-for-sale as of December 31, 2017 included $36.8 million and $3.3 million, representing our Utica Shale properties and field office facilities and a separate parcel of land, respectively.

The following table presents balance sheet data related to assets held-for-sale. Assets held-for-sale represents the assets that are expected to be sold, net of liabilities that are expected to be assumed by the purchasers:



	March 31, 2018		December 31, 2017
	(in thousands)
Assets
Properties and equipment, net	$	1,647	$	40,583
Total assets	$	1,647	$	40,583

Liabilities
Asset retirement obligation	$	—	$	499
Total liabilities	$	—	$	499

Assets held-for-sale, net	$	1,647	$	40,084

Suspended Well Costs. We have spud three wells in the Delaware Basin for which we are unable to make a final determination regarding whether proved reserves can be associated with the wells as of March 31, 2018 as the wells had not been completed as of that date. Therefore, we have classified the capitalized costs of the wells as suspended well costs as of March 31, 2018 while we continue to conduct completion and testing operations to determine the existence of proved reserves.

The following table presents the capitalized exploratory well cost pending determination of proved reserves and included in properties and equipment, net on the condensed consolidated balance sheets:



	March 31, 2018		December 31, 2017
	(in thousands, except for number of wells)

Beginning balance	$	15,448	$	—
Additions to capitalized exploratory well costs pending the determination of proved reserves	17,143		51,776
Reclassifications to proved properties	—		(36,328		)
Ending balance	$	32,591	$	15,448

Number of wells pending determination at period end	3		3

Exploration, geologic, and geophysical expense. Exploration, geologic, and geophysical expense of $2.6 million during the three months ended March 31, 2018 was primarily related to the purchase of seismic data related to unproved acreage and lease costs associated with certain delayed drilling in the Delaware Basin. Exploration, geologic, and geophysical expense of $1.0 million during the three months ended March 31, 2017 was primarily related to drilling pilot holes in the Delaware Basin.