Unevaluated Property

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Unevaluated Property

Note 5. Unevaluated Property

A summary of the unevaluated property costs excluded from oil and natural gas properties being amortized at December 31, 2018, and the year in which the costs were incurred follows:

	December 31, 2018
	Costs Incurred During:
In thousands	2018		2017		2016		2015 and Prior		Total
Property acquisition costs	$	—	$	8,527	$	—	$	582,364	$	590,891
Exploration and development	9,849		6,948		20,673		189,890		227,360
Capitalized interest	36,510		30,762		25,220		85,957		178,449
Total	$	46,359	$	46,237	$	45,893	$	858,211	$	996,700

Our property acquisition costs for 2015 and prior were primarily related to the fair value allocated to the purchase of interests in the Cedar Creek Anticline (“CCA”) and Hartzog Draw, as well as CO₂ tertiary potential at Conroe Field. Exploration and development costs shown as unevaluated properties are primarily associated with our tertiary oil fields that are under development but did not have proved reserves at December 31, 2018.  The most significant development costs incurred during each period relate to development in preparation for the CO₂ floods at Grieve and Webster fields. We have not yet recognized proved tertiary reserves in these fields.

Costs are transferred into the amortization base on an ongoing basis as projects are evaluated and proved reserves established or impairment determined.  We review the excluded properties for impairment at least annually.  We currently estimate that evaluation of the majority of these properties and the inclusion of their costs in the amortization base is expected to be completed withinfivetotenyears.  Until we are able to determine whether there are any proved reserves attributable to the above costs, we are not able to assess the future impact on the amortization rate of the full cost pool.