Disclosures about oil and natural gas activities (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Oil And Gas Exploration And Production Industries Disclosures [Abstract]

Summary of changes in quantities of proved oil and natural gas reserves

Our oil and natural gas reserves are attributable solely to properties within the United States. A summary of the changes in our quantities of proved oil and natural gas reserves for the three years ended December 31, 2017 are as follows:

	Oil (MBbls)			Natural gas (MMcf)			Natural gas liquids (MBbls)			Total (MBoe)
Proved developed and undeveloped reserves
As of January 1, 2015		101,247			247,756			16,853			159,393
Purchase of minerals in place		38			1,120			46			271
Sales of minerals in place		(2,225	)		(3,656	)		(117	)		(2,951	)
Extensions and discoveries		3,651			13,759			1,096			7,040
Revisions (1)		(19,840	)		(61,973	)		(4,257	)		(34,426	)
Improved recoveries (2)		36,414			—			—			36,414
Production		(5,519	)		(18,788	)		(1,550	)		(10,200	)
Balance at December 31, 2015		113,766			178,218			12,071			155,541
Extensions and discoveries		4,037			18,085			1,499			8,550
Revisions (1)		(16,312	)		(44,965	)		(57	)		(23,864	)
Production		(4,870	)		(15,889	)		(1,408	)		(8,926	)
Balance at December 31, 2016		96,621			135,449			12,105			131,301
Sales of minerals in place		(74,918	)		(1,663	)		(46	)		(75,241	)
Extensions and discoveries		8,957			39,843			5,442			21,040
Revisions (1)		3,515			11,135			2,216			7,586
Production		(4,571	)		(14,598	)		(1,395	)		(8,399	)
Balance at December 31, 2017		29,604			170,166			18,322			76,287
Proved developed reserves:
January 1, 2015		54,862			158,265			11,787			93,027
December 31, 2015		40,300			132,323			9,169			71,524
December 31, 2016		28,590			108,800			9,352			56,076
December 31, 2017		18,301			123,451			11,858			50,734
Proved undeveloped reserves:
January 1, 2015		46,385			89,491			5,066			66,366
December 31, 2015		73,466			45,895			2,902			84,017
December 31, 2016		68,031			26,649			2,753			75,225
December 31, 2017		11,303			46,715			6,464			25,553

(1) The upward revision in 2017 was due to changes in pricing and costs. The downward revision in our reserves during 2016 was primarily due to removing proved undeveloped reserves that are not expected to be developed within the five-year time frame mandated by the SEC, revision in the base water flood decline curve at our North Burbank Unit, and the decline in SEC pricing. The downward revision in our reserves during 2015 was primarily due to the decline in SEC pricing which resulted in future extraction of certain reserves being uneconomic.

(2) Improved recoveries in 2015 resulted from the addition of reserves from remaining future phases of CO₂ injection at our North Burbank EOR unit.

Standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves

The standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves are as follows:

	Successor			Predecessor
	December 31,			December 31,
	2017			2016			2015
Future cash flows	$	2,331,940		$	4,635,481		$	6,327,363
Future production costs		(899,380	)		(1,998,001	)		(2,670,692	)
Future development and abandonment costs		(336,828	)		(1,147,390	)		(1,536,063	)
Future income tax provisions		—			—			(89,999	)
Net future cash flows		1,095,732			1,490,090			2,030,609
Less effect of 10% discount factor		(597,859	)		(961,309	)		(1,345,920	)
Standardized measure of discounted future net cash flows	$	497,873		$	528,781		$	684,689

Changes in standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves

The changes in the standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves are as follows:

	For the year ended December 31,
	2017			2016			2015
Beginning of year	$	528,781		$	684,689		$	1,894,700
Sale of oil and natural gas produced, net of production costs		(175,246	)		(141,732	)		(196,319	)
Net changes in prices and production costs		125,795			(296,299	)		(2,230,601	)
Extensions and discoveries		136,887			79,990			101,384
Improved recoveries		—			—			524,436
Changes in future development costs		(4,879	)		278,653			204,199
Development costs incurred during the period that reduced future    development costs		37,912			63,894			80,103
Revisions of previous quantity estimates (1)		68,428			(223,218	)		(495,794	)
Purchases and sales of reserves in place, net		(238,445	)		—			(47,079	)
Accretion of discount		24,267			68,545			237,134
Net change in income taxes		—			21,139			605,766
Changes in production rates and other		(5,627	)		(6,880	)		6,760
End of year	$	497,873		$	528,781		$	684,689

(1) Amounts in 2017 are primarily the result of increased volumes due to changes in pricing and costs. Amounts in 2016 are primarily the result of removing proved undeveloped reserves that are not expected to be developed within the five years, a revision in the base water flood decline curve at our North Burbank Unit and the decline in SEC pricing which resulted in future extraction of certain reserves being uneconomic. Amounts in 2015 are primarily the result of the decrease in SEC pricing, lower margins on existing reserves and a decrease in taxes as a result of the lower margins.

Prices Used In Determining Future Net Revenues Related To The Standardized Measure Of Discounted Future Cash Flows Table Text Block

The following prices for oil, natural gas, and natural gas liquids before field differentials were used in determining future net revenues related to the standardized measure calculation.

	2017		2016		2015
Oil (per Bbl)	$	51.34	$	42.75	$	50.28
Natural gas (per Mcf)	$	2.98	$	2.49	$	2.58
Natural gas liquids (per Bbl)	$	24.17	$	13.47	$	15.84