NOTE 6. OIL AND NATURAL GAS PROPERTIES

Oil and natural gas properties consisted of the following as of December 31:

	2016			2015
Proved oil and natural gas properties:
Well and development costs	$	118,245		$	71,463
Accumulated depletion		(20,204	)		—
Total proved properties		98,041			71,463

Unproved oil and natural gas properties:
Oil and natural gas leaseholds		651,295			738,852
Accumulated valuation allowance		(507,198	)		(178,463	)
		144,097			560,389
Exploratory wells in process		836,747			1,727,181
Total unproved properties		980,844			2,287,570

Total oil and natural gas properties, net	$	1,078,885		$	2,359,033

Capitalized Exploratory Well Costs

The following tables reflect the net changes in and the cumulative costs of capitalized exploratory well costs (excluding any related leasehold costs):

	2016			2015			2014
Beginning of period	$	1,727,181		$	1,186,464		$	777,823
Additions to capitalized exploration
Exploratory well costs		499,985			630,395			522,892
Capitalized interest		99,541			87,683			51,208
Amounts charged to expense ⁽¹⁾		(1,489,960	)		(177,361	)		(165,459	)
End of period	$	836,747		$	1,727,181		$	1,186,464

⁽¹⁾	Amounts represent dry hole costs related to exploratory wells which did not encounter commercial hydrocarbons or where it was determined that sufficient progress was not being made.

	2016		2015
Cumulative costs:
Exploratory well costs	$	582,115	$	1,572,090
Capitalized interest		254,632		155,091
	$	836,747	$	1,727,181
Wells costs capitalized for a period greater than one year after completion after drilling (included in table above)	$	609,893	$	1,225,747

As of December 31, 2016, capitalized exploratory well costs that have been suspended longer than one year are associated with our Shenandoah, North Platte, Anchor, and Gabon discoveries. As of December 31, 2015, capitalized exploratory well costs that have been suspended longer that one year as associated with our Shenandoah, North Platte, Anchor, Gabon and Angolan discoveries. These well costs are suspended pending ongoing evaluation including, but not limited to, results of additional appraisal drilling, well–test analysis, additional geological and geophysical data and approval of a development plan. We believe these discoveries exhibit sufficient indications of hydrocarbons to justify potential development and are actively pursuing efforts to fully assess them. If additional information becomes available that raises substantial doubt as to the economic or operational viability of these discoveries, the associated costs will be expensed at that time.