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)

v3.8.0.1
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, 2017
MMBoe
Bcfe
MMBbls
Bcf
Dec. 31, 2016
MMBoe
Bcfe
MMBbls
Bcf
Dec. 31, 2015
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 32.9 35.5 61.7
Revisions of previous estimates 4.5 [1] 4.6 [2] 4.8 [3]
Revisions related to sold properties [4]     (12.1)
Extensions and discoveries 4.1 [5]   2.4 [6]
Sales of reserves [7]     (13.5)
Production (7.1) (7.2) (7.8)
Proved reserves, ending balance 34.4 32.9 35.5
Oil | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 26.6 29.4  
Proved reserves, ending balance 26.1 26.6 29.4
Oil | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 6.3 6.1  
Proved reserves, ending balance 8.3 [8] 6.3 6.1
NGLs      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 8.2 6.6 15.8
Revisions of previous estimates 0.7 [1] 3.1 [2] (0.9) [3]
Revisions related to sold properties [4]     (4.8)
Extensions and discoveries 0.3 [5]   0.2 [6]
Sales of reserves [7]     (2.1)
Production (1.4) (1.5) (1.6)
Proved reserves, ending balance 7.8 8.2 6.6
NGLs | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 7.6 6.4  
Proved reserves, ending balance 7.2 7.6 6.4
NGLs | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 0.6 0.2  
Proved reserves, ending balance 0.6 [8] 0.6 0.2
Natural Gas      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 197,800 205,400 254,900
Revisions of previous estimates | Bcf 25,800 [1] 32,100 [2] 4,900 [3]
Revisions related to sold properties | Bcf [4]     (2,900)
Extensions and discoveries | Bcf 5,400 [5]   8,800 [6]
Purchase of minerals in place | Bcf [9]     6,100
Sales of reserves | Bcf [7]     (20,200)
Production | Bcf (36,800) (39,700) (46,200)
Proved reserves, ending balance | Bcf 192,200 197,800 205,400
Natural Gas | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 183,100 198,500  
Proved reserves, ending balance | Bcf 173,500 183,100 198,500
Natural Gas | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcf 14,700 6,900  
Proved reserves, ending balance | Bcf 18,700 [8] 14,700 6,900
Barrel Equivalent      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [10] 74.0 76.4 120.0
Revisions of previous estimates | MMBoe [10] 9.6 [1] 13.0 [2] 4.7 [3]
Revisions related to sold properties | MMBoe [4],[10]     (17.4)
Extensions and discoveries | MMBoe [10] 5.2 [5]   4.1 [6]
Purchase of minerals in place | MMBoe [9],[10]     1.0
Sales of reserves | MMBoe [7],[10]     (19.0)
Production | MMBoe [10] (14.6) (15.4) (17.0)
Proved reserves, ending balance | MMBoe [10] 74.2 74.0 76.4
Barrel Equivalent | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [10] 64.7 69.0  
Proved reserves, ending balance | MMBoe [10] 62.2 64.7 69.0
Barrel Equivalent | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | MMBoe [10] 9.3 7.4  
Proved reserves, ending balance | MMBoe [10] 12.0 [8] 9.3 7.4
Natural Gas Equivalent      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [10] 444.0 458.1 720.0
Revisions of previous estimates | Bcfe [10] 57.4 [1] 78.1 [2] 28.0 [3]
Revisions related to sold properties | Bcfe [4],[10]     (104.3)
Extensions and discoveries | Bcfe [10] 31.3 [5]   24.4 [6]
Purchase of minerals in place | Bcfe [9],[10]     6.1
Sales of reserves | Bcfe [7],[10]     (113.8)
Production | Bcfe [10] (87.4) (92.2) (102.3)
Proved reserves, ending balance | Bcfe [10] 445.3 444.0 458.1
Natural Gas Equivalent | Proved Developed Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [10] 388.2 413.5  
Proved reserves, ending balance | Bcfe [10] 373.3 388.2 413.5
Natural Gas Equivalent | Proved Undeveloped Reserves      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance | Bcfe [10] 55.8 44.6  
Proved reserves, ending balance | Bcfe [10] 72.0 [8] 55.8 44.6
[1] 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 (Virgo) field. Additionally, increases of 3.4 MMBoe were due to price revisions.
[2] Primarily related to upward revisions of 14.2 MMBoe, which included upward revisions of 3.8 MMBoe at our Viosca Knoll 823 (Tahoe/SE Tahoe) 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.
[3] Includes upwards revisions of 7.4 MMBoe at the Ship Shoal 349 field (Mahogany), 1.9 MMBoe at our Brazo A-133 field, 1.3 MMBoe at out Atwater 575 field, 1.3 MMBoe at out Mississippi Canyon 243 field (Matterhorn), 1.1 MMBoe at our Fairway Field, partially offset by downward revisions due to price of 10.7 MMBoe. The revision for price excludes the Yellow Rose field sold during 2015.
[4] Revisions related to the Yellow Rose field during 2015, which were primarily due to price reductions, up to the date of the sale in October 2015.
[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 due to increases at our Ewing Bank 910 field.
[7] Related primarily to the sale of the Yellow Rose field in October 2015, which had estimated reserves at the date of sale of 19.0 MMBoe.
[8] We believe that we will be able to develop all but 1.8 MMBoe (approximately 15%) of the total of 12.0 MMBoe reserves classified as proved undeveloped (“PUDs”) at December 31, 2017, within five years from the date such reserves were initially recorded. The lone exceptions are at the Mississippi Canyon 243 field (Matterhorn) where the field is being developed using a single floating tension leg platform requiring an extended sequential development plan. The platform cannot support a rig that would allow additional wells to be drilled, but can support a rig to allow sidetracking of wells. Two sidetrack PUD locations in this 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 2023.
[9] Primarily due to purchase of additional interest at our Brazos A-133 field.
[10] 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.