Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, NGLs and Natural Gas Reserves (Details)

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Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, NGLs and Natural Gas Reserves (Details)
Bcfe in Millions
 12 Months Ended
Dec. 31, 2018
MMBoe
Bcfe
MMBbls
Bcf
Dec. 31, 2017
MMBoe
Bcfe
MMBbls
Bcf
Dec. 31, 2016
MMBoe
Bcfe
MMBbls
Bcf
Reserve Quantities [Line Items]      
Revisions of previous estimates | MMBoe   6.2 14.2
Oil      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 34.4 32.9 35.5
Revisions of previous estimates 11.6 [1] 4.5 [2] 4.6 [3]
Extensions and discoveries 0.5 [4] 4.1 [5]  
Purchase of minerals in place [6] 1.5    
Sales of minerals in place [7] (2.2)    
Production (6.7) (7.1) (7.2)
Proved reserves, ending balance 39.1 34.4 32.9
Oil | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 26.1 26.6  
Proved reserves, ending balance 31.5 26.1 26.6
Oil | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 8.3 6.3  
Proved reserves, ending balance 7.6 [8] 8.3 6.3
NGLs      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 7.8 8.2 6.6
Revisions of previous estimates 2.8 [1] 0.7 [2] 3.1 [3]
Extensions and discoveries 0.3 [4] 0.3 [5]  
Purchase of minerals in place [6] 0.4    
Sales of minerals in place [7] (0.2)    
Production (1.3) (1.4) (1.5)
Proved reserves, ending balance 9.8 7.8 8.2
NGLs | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 7.2 7.6  
Proved reserves, ending balance 7.8 7.2 7.6
NGLs | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 0.6 0.6  
Proved reserves, ending balance 2.0 [8] 0.6 0.6
Natural Gas      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 192,200 197,800 205,400
Revisions of previous estimates | Bcf 40,400 [1] 25,800 [2] 32,100 [3]
Extensions and discoveries | Bcf 7,700 [4] 5,400 [5]  
Purchase of minerals in place | Bcf [6] 9,400    
Sales of minerals in place | Bcf [7] (7,200)    
Production | Bcf (32,000) (36,800) (39,700)
Proved reserves, ending balance | Bcf 210,500 192,200 197,800
Natural Gas | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 173,500 183,100  
Proved reserves, ending balance | Bcf 166,800 173,500 183,100
Natural Gas | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 18,700 14,700  
Proved reserves, ending balance | Bcf 43,700 [8] 18,700 14,700
Barrel Equivalent      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [9] 74.2 74.0 76.4
Revisions of previous estimates | MMBoe [9] 21.1 [1] 9.6 [2] 13.0 [3]
Extensions and discoveries | MMBoe [9] 2.1 [4] 5.2 [5]  
Purchase of minerals in place | MMBoe [6],[9] 3.4    
Sales of minerals in place | MMBoe [7],[9] (3.5)    
Production | MMBoe [9] (13.3) (14.6) (15.4)
Proved reserves, ending balance | MMBoe [9] 84.0 74.2 74.0
Barrel Equivalent | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [9] 62.2 64.7  
Proved reserves, ending balance | MMBoe [9] 67.0 62.2 64.7
Barrel Equivalent | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [9] 12.0 9.3  
Proved reserves, ending balance | MMBoe [9] 17.0 [8] 12.0 9.3
Natural Gas Equivalent      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [9] 445.3 444.0 458.1
Revisions of previous estimates | Bcfe [9] 126.7 [1] 57.4 [2] 78.1 [3]
Extensions and discoveries | Bcfe [9] 12.6 [4] 31.3 [5]  
Purchase of minerals in place | Bcfe [6],[9] 20.7    
Sales of minerals in place | Bcfe [7],[9] (21.2)    
Production | Bcfe [9] (80.0) (87.4) (92.2)
Proved reserves, ending balance | Bcfe [9] 504.1 445.3 444.0
Natural Gas Equivalent | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [9] 373.3 388.2  
Proved reserves, ending balance | Bcfe [9] 402.2 373.3 388.2
Natural Gas Equivalent | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [9] 72.0 55.8  
Proved reserves, ending balance | Bcfe [9] 101.9 [8] 72.0 55.8
[1] Primarily related to upward revisions of 13.8 MMBoe at our Mahogany field and of 5.4 MMBoe at our Ship Shoal 028 field. Additionally, increases of 2.3 MMBoe were due to price revisions.
[2] Primarily related to upward revisions of 6.2 MMBoe, which included upwards revisions of 1.1 MMBoe at our Mississippi Canyon 698 (Big Bend) field, 1.0 MMBoe at our Fairway field, 0.8 MMBoe at our Ewing Bank 910 field and 0.8 MMBoe at our Viosca Knoll 783 (Tahoe/SE Tahoe) field. Additionally, increases of 3.4 MMBoe were due to price revisions.
[3] Primarily related to upward revisions of 14.2 MMBoe, which included upward revisions of 3.8 MMBoe at our Virgo field, 1.5 MMBoe at our Fairway field, 1.3 MMBoe at our Mississippi Canyon 782 (Dantzler) field, and 1.2 MMBoe at our Main Pass 108 field. Partially offsetting were decreases for price revisions of 1.2 MMBoe.
[4] Primarily related to extensions and discoveries of 1.3 MMBoe at our Virgo field and 0.7 MMBoe at our Ewing Bank 910 field.
[5] Primarily related to extensions and discoveries at our Ship Shoal 349 (Mahogany) field of 3.5 MMBoe and at our Main Pass 286 field of 1.5 MMBoe.
[6] Primarily related to our Ship Shoal 028 field and our Green Canyon 859 field (Heidelberg).
[7] Primarily related to conveyance of interest in properties related to the JV Drilling Program.
[8] We believe that we will be able to develop all but 1.8 MMBoe (approximately 11%) of the total of 17.0 MMBoe reserves classified as proved undeveloped (“PUDs”) at December 31, 2018, within five years from the date such reserves were initially recorded. The lone exceptions are at the Mississippi Canyon 243 field (Matterhorn) and Virgo deepwater fields where future development drilling has been planned as sidetracks of existing wellbores due to conductor slot limitations and rig availability. Two sidetrack PUD locations, one in each field, will be delayed until an existing well is depleted and available to sidetrack. Based on the latest reserve report, these PUD locations are expected to be developed in 2021 and 2022, respectively.
[9] The conversion to barrels of oil equivalent and cubic feet equivalent were determined using the energy-equivalent ratio of six Mcf of natural gas to one barrel of crude oil, condensate or NGLs (totals may not compute due to rounding). The energy-equivalent ratio does not assume price equivalency, and the energy-equivalent prices for crude oil, NGLs and natural gas may differ significantly.