Property, Plant and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property, plant and equipment consists of the following (in thousands):


	December 31,
	2019		2018
Oil and natural gas properties
Proved	$	1,484,359	$	1,269,091
Unproved	24,603		60,152
Total oil and natural gas properties	1,508,962		1,329,243
Less accumulated depreciation, depletion and impairment	(1,129,622)		(580,132)
Net oil and natural gas properties capitalized costs	379,340		749,111

Land	4,400		4,400
Electrical infrastructure	126,482		131,176
Non-oil and natural gas equipment	12,665		13,458
Buildings and structures	77,148		77,148
Financing Leases	2,109		—
Total	222,804		226,182
Less accumulated depreciation and amortization	(34,201)		(25,344)
Other property, plant and equipment, net	188,603		200,838
Total property, plant and equipment, net	$	567,943	$	949,949

The average rates used for depreciation and depletion of oil and natural gas properties were $12.28 per Boe in 2019, $10.32 per Boe in 2018 and $7.92 per Boe in 2017.

See Note 9 for discussion of impairment of other property, plant and equipment.

Costs Excluded from Amortization

The following table summarizes the costs, by year incurred, related to unproved properties, which were excluded from oil and natural gas properties subject to amortization at December 31, 2019 (in thousands):


			Year Cost Incurred
	Total		2019		2018		2017		2016 and Prior
Property acquisition	$	23,973	$	2,653	$	2,353	$	4,280	$	14,687
Exploration	630		10		16		564		40
Total costs incurred	$	24,603	$	2,663	$	2,369	$	4,844	$	14,727

For leases that do not have existing production that would otherwise extend the lease term, the Company estimates that any associated unproved costs will be evaluated and transferred to the amortization base of the full cost pool within a three to five year period from the original lease date. For leases that are held by production, the Company estimates that any associated unproved costs will be evaluated and transferred to the amortization base of the full cost pool within a 10-year period from the original lease date. In addition, the Company’s internal engineers evaluate all properties on a quarterly basis.