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

12 Months Ended

Dec. 31, 2018

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

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

A summary of the changes in our quantities of proved oil and natural gas reserves for the three years ended December 31, 2018 are as follows:

	Oil (MBbls)		Natural gas (MMcf)		Natural gas liquids (MBbls)		Total (MBoe)
Proved developed and undeveloped reserves
As of January 1, 2016	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
Sales of minerals in place	(2,422	)	(14,184	)	(1,374	)	(6,160	)
Extensions and discoveries	6,545		69,189		9,329		27,406
Revisions (1)	1,254		12,596		1,411		4,764
Production	(2,684	)	(17,549	)	(1,881	)	(7,490	)
Balance at December 31, 2018	32,297		220,218		25,807		94,807
Proved developed reserves:
January 1, 2016	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
December 31, 2018	18,051		135,425		14,846		55,468
Proved undeveloped reserves:
January 1, 2016	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
December 31, 2018	14,246		84,793		10,961		39,339

(1) The upward revision in 2018 was primarily due to changes in prices. The upward revision in 2017 was primarily 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.

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,
	2018			2017			2016
Future cash flows	$	3,255,771		$	2,331,940		$	4,635,481
Future production costs	(1,187,071		)	(899,380		)	(1,998,001		)
Future development and abandonment costs	(450,220		)	(336,828		)	(1,147,390		)
Future income tax provisions	—			—			—
Net future cash flows	1,618,480			1,095,732			1,490,090
Less effect of 10% discount factor	(932,114		)	(597,859		)	(961,309		)
Standardized measure of discounted future net cash flows	$	686,366		$	497,873		$	528,781

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,
	2018			2017			2016
Beginning of year	$	497,873		$	528,781		$	684,689
Sale of oil and natural gas produced, net of production costs	(175,199		)	(175,246		)	(141,732		)
Net changes in prices and production costs	95,430			125,795			(296,299		)
Extensions and discoveries	192,105			136,887			79,990
Improved recoveries	—			—			—
Changes in future development costs	(2,424		)	(4,879		)	278,653
Development costs incurred during the period that reduced future    development costs	6,277			37,912			63,894
Revisions of previous quantity estimates (1)	79,192			68,428			(223,218		)
Purchases and sales of reserves in place, net	(45,222		)	(238,445		)	—
Accretion of discount	36,386			24,267			68,545
Net change in income taxes	—			—			21,139
Changes in production rates and other	1,948			(5,627		)	(6,880		)
End of year	$	686,366		$	497,873		$	528,781

(1) Amount in 2018 are primarily the result of changes in pricing. 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.

Prices used In determining future net revenues related to the standardized measure of discounted future cash flows

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.

	2018		2017		2016
Oil (per Bbl)	$	65.56	$	51.34	$	42.75
Natural gas (per Mcf)	$	3.10	$	2.98	$	2.49
Natural gas liquids (per Bbl)	$	25.56	$	24.17	$	13.47