W&T Offshore, Inc. Annual report pursuant to Section 13 and 15(d)

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)

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

12 Months Ended

Dec. 31, 2014

MMBbls

Dec. 31, 2013

MMBbls

Dec. 31, 2012

MMBbls

Oil

Reserve Quantities [Line Items]

Proved reserves, beginning balance

58.5

54.8

51.4

Revisions of previous estimates

1.6

^[1]

(4.3)

^[2]

(1.1)

^[3]

Extensions and discoveries

7.3

^[4]

13.9

^[5]

8.2

^[6]

Purchase of minerals in place

1.5

^[7]

1.5

^[8]

2.5

^[9]

Sales of reserves

(0.4)

^[10]

(0.2)

^[11]

Production

(7.2)

(7.0)

(6.0)

Proved reserves, ending balance

61.7

58.5

54.8

Oil | Proved Developed Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

35.7

36.2

35.3

Oil | Proved Undeveloped Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

26.0

^[12]

22.3

19.5

NGLs

Reserve Quantities [Line Items]

Proved reserves, beginning balance

15.9

15.2

17.1

Revisions of previous estimates

0.1

^[1]

0.2

^[2]

(2.6)

^[3]

Extensions and discoveries

0.7

^[4]

2.6

^[5]

2.6

^[6]

Purchase of minerals in place

1.2

^[7]

0.2

^[9]

Production

(2.1)

Proved reserves, ending balance

15.8

15.9

15.2

NGLs | Proved Developed Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

10.7

11.1

11.0

NGLs | Proved Undeveloped Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

5.1

^[12]

4.8

4.2

Natural Gas

Reserve Quantities [Line Items]

Proved reserves, beginning balance

259,900

285,100

289,700

Revisions of previous estimates

14,300

^[1]

2,100

^[2]

(4,800)

^[3]

Extensions and discoveries

10,100

^[4]

22,000

^[5]

29,600

^[6]

Purchase of minerals in place

20,700

^[7]

4,400

^[8]

25,500

^[9]

Sales of reserves

(400)

^[10]

(1,100)

^[11]

Proved reserves, ending balance

254,900

259,900

285,100

Natural Gas | Proved Developed Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

221,100

232,700

243,500

Natural Gas | Proved Undeveloped Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

33,800

^[12]

27,200

41,600

Barrel Equivalent

Reserve Quantities [Line Items]

Proved reserves, beginning balance

117.7

^[13]

117.5

^[13]

116.9

^[13]

Revisions of previous estimates

4.1

^[1],[13]

(3.8)

^[13],[2]

(4.6)

^[13],[3]

Extensions and discoveries

9.7

^[13],[4]

20.2

^[13],[5]

15.7

^[13],[6]

Purchase of minerals in place

6.1

^[13],[7]

2.3

^[13],[8]

7.0

^[13],[9]

Sales of reserves

(0.5)

^[10],[13]

(0.4)

^[11],[13]

Production

(17.6)

^[13]

(18.0)

^[13]

(17.1)

^[13]

Proved reserves, ending balance

120.0

^[13]

117.7

^[13]

117.5

^[13]

Barrel Equivalent | Proved Developed Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

83.3

^[13]

86.1

^[13]

86.9

^[13]

Barrel Equivalent | Proved Undeveloped Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

36.7

^[12],[13]

31.6

^[13]

30.6

^[13]

Natural Gas Equivalent

Reserve Quantities [Line Items]

Proved reserves, beginning balance

705,900,000

^[13]

705,100,000

^[13]

701,100,000

^[13]

Revisions of previous estimates

25,300,000

^[1],[13]

(22,800,000)

^[13],[2]

(27,500,000)

^[13],[3]

Extensions and discoveries

58,100,000

^[13],[4]

121,000,000

^[13],[5]

94,500,000

^[13],[6]

Purchase of minerals in place

^[13],[7]

^[13],[8]

^[13],[9]

^[10],[13]

^[11],[13]

^[13]

^[13]

^[13]

Proved reserves, ending balance

720,000,000

^[13]

705,900,000

^[13]

705,100,000

^[13]

Natural Gas Equivalent | Proved Developed Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

499,700,000

^[13]

516,100,000

^[13]

521,200,000

^[13]

Natural Gas Equivalent | Proved Undeveloped Reserves

Reserve Quantities [Line Items]

Proved reserves, ending balance

220,300,000

^[12],[13]

189,800,000

^[13]

183,900,000

^[13]

[1]	Includes upwards revisions due to price of 0.3 MMBoe; positive revisions of 2.4 MMBoe at our Fairway field, 1.2 MMBoe at our Mississippi Canyon 800 field and 6.4 MMBoe at various fields; and negative revisions of 3.9 MMBoe at our Spraberry field and 2.4 MMBoe at various other fields.
[2]	Includes upward revision due to price of 1.9 MMBoe; negative revisions of 4.9 MMBoe at our Spraberry field for performance and technical changes, 2.3 MMBoe at our High Island 21/22 field for performance, 1.3 MMBoe at our Ship Shoal 349/359 field for performance; and positive performance revisions of 0.7 MMBoe at our Main Pass 98 field, 0.7 MMBoe at our South Timbalier 314, 0.6 MMBoe at our Main Pass 108 field and 0.5 MMBoe our South Timbalier 176 field.
[3]	Includes downward revisions due to price of 1.3 MMBoe and negative performance revisions of 3.0 MMBoe at our Spraberry field.
[4]	Includes extensions and discoveries of 4.1 MMBoe at our Spraberry field and 4.1 MMBoe at our Mississippi Canyon 782 field.
[5]	Includes extensions and discoveries of 12.6 MMBoe at our Spraberry field, 4.2 MMBoe at our Ship Shoal 349 field and 1.9 MMBoe at our Mississippi Canyon 698 field.
[6]	Includes extensions and discoveries of 11.6 MMBoe at our Spraberry field and extensions and discoveries of 2.7 MMBoe at our High Island 21/22 field.
[7]	Primarily due to acquiring additional ownership in the Fairway field and acquisition of the Woodside Properties.
[8]	Primarily due to the acquisition of the Callon Properties.
[9]	Due to the acquisition of the Newfield Properties.
[10]	Primarily due to the sales of our non-working interests in the Green Canyon 60 field, the Green Canyon 19 field and the West Delta area block 29.
[11]	Due to the sale of our interest in the South Timbalier 41 field.
[12]	We believe that we will be able to develop all but 1.4 MMBoe of the reserves classified as proved undeveloped (“PUDs”), or approximately 96%, out of the total of 36.7 MMBoe classified as PUDs at December 31, 2014, within five years from the date such reserves were initially recorded. The exception is 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. These PUDs were originally recorded in our reserves as of December 31, 2010. The development of the 1.4 MMBoe of PUDs will be delayed until an existing well is depleted and available to sidetrack. Based on the latest reserve report, a well is expected to be drilled to develop the Mississippi Canyon 243 field (Matterhorn) PUDs in 2020.
[13]	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 Bbl 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 oil, NGLs and natural gas may differ significantly.