v3.8.0.1

Disclosures About Oil and Gas Producing Activities (unaudited) (Tables) | 12 Months Ended
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Dec. 31, 2017
Extractive Industries [Abstract] |
Commodity Prices Inclusive of Adjustments for Quality and Location Used in Determining Future Net Revenues Related to Standardized Measure Calculation | The following table summarizes the prices used in the reserve estimates for 2017, 2016 and 2015. Commodity prices used for the reserve estimates, adjusted for basis differentials, grade and quality, are as follows:
|  | 2017 |  |  | 2016 |  |  | 2015 |
Oil (per Bbl) |  | $ | 51.34 |  |  | $ | 42.69 |  |  | $ | 50.16 |
Natural gas liquids (per Bbl) |  | $ | 18.67 |  |  | $ | 14.12 |  |  | $ | 15.13 |
Gas (per Mcf) |  | $ | 2.99 |  |  | $ | 2.47 |  |  | $ | 2.64 |
Summary of Changes in Quantities of Proved Oil, NGL and Natural Gas Reserves | The following table provides a summary of the changes of the total proved reserves for the years ended December 31, 2017, 2016 and 2015, as well as proved developed and proved undeveloped reserves at the beginning and end of each respective year.
Total Proved Reserves |  | Oil (MBbls) |  |  | NGLs (MBbls) |  |  | Natural Gas (MMcf) |  |  | Total (MBoe) |
Balance — January 1, 2015 |  |  | 55,338 |  |  |  | 40,907 |  |  |  | 300,020 |  |  |  | 146,248 |
Extensions and discoveries |  |  | 11,054 |  |  |  | 10,630 |  |  |  | 79,268 |  |  |  | 34,895 |
Production(1) |  |  | (1,882 | ) |  |  | (1,694 | ) |  |  | (13,262 | ) |  |  | (5,787 | )
Revisions to previous estimates |  |  | (10,014 | ) |  |  | (357 | ) |  |  | 9,962 |  |  |  | (8,710 | )
Balance — December 31, 2015 |  |  | 54,496 |  |  |  | 49,486 |  |  |  | 375,988 |  |  |  | 166,646 |
Extensions and discoveries |  |  | 6,529 |  |  |  | 4,564 |  |  |  | 33,347 |  |  |  | 16,651 |
Production(1) |  |  | (1,275 | ) |  |  | (1,529 | ) |  |  | (11,734 | ) |  |  | (4,759 | )
Revisions to previous estimates |  |  | (9,719 | ) |  |  | (4,887 | ) |  |  | (45,324 | ) |  |  | (22,161 | )
Balance — December 31, 2016 |  |  | 50,031 |  |  |  | 47,634 |  |  |  | 352,277 |  |  |  | 156,377 |
Extensions and discoveries |  |  | 10,546 |  |  |  | 9,975 |  |  |  | 76,710 |  |  |  | 33,307 |
Acquisition of minerals in place |  |  | 710 |  |  |  | 394 |  |  |  | 2,808 |  |  |  | 1,572 |
Production(1) |  |  | (1,107 | ) |  |  | (1,486 | ) |  |  | (11,148 | ) |  |  | (4,452 | )
Revisions to previous estimates |  |  | (10,120 | ) |  |  | 1,431 |  |  |  | 20,581 |  |  |  | (5,259 | )
Balance — December 31, 2017 |  |  | 50,060 |  |  |  | 57,948 |  |  |  | 441,228 |  |  |  | 181,545 |
(1) | Production included 1,530 MMcf, 1,330 MMcf and 1,319 MMcf related to field fuel in 2015, 2016 and 2017, respectively.
Total Proved Reserves |  | Oil (MBbls) |  |  | NGLs (MBbls) |  |  | Natural Gas (MMcf) |  |  | Total (MBoe) |
Proved Developed Reserves: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
January 1, 2015 |  |  | 17,978 |  |  |  | 19,082 |  |  |  | 138,961 |  |  |  | 60,220 |
December 31, 2015 |  |  | 15,667 |  |  |  | 20,414 |  |  |  | 154,652 |  |  |  | 61,856 |
December 31, 2016 |  |  | 13,466 |  |  |  | 20,375 |  |  |  | 150,208 |  |  |  | 58,875 |
December 31, 2017 |  |  | 13,853 |  |  |  | 23,180 |  |  |  | 176,201 |  |  |  | 66,399 |
Proved Undeveloped Reserves: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
January 1, 2015 |  |  | 37,360 |  |  |  | 21,825 |  |  |  | 161,059 |  |  |  | 86,028 |
December 31, 2015 |  |  | 38,829 |  |  |  | 29,072 |  |  |  | 221,335 |  |  |  | 104,790 |
December 31, 2016 |  |  | 36,565 |  |  |  | 27,259 |  |  |  | 202,069 |  |  |  | 97,502 |
December 31, 2017 |  |  | 36,207 |  |  |  | 34,768 |  |  |  | 265,028 |  |  |  | 115,146 |
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Natural Gas Reserves | The following table provides the standardized measure of discounted future net cash flows at December 31, 2017, 2016 and 2015 (in thousands):
|  | Years Ended December 31, |
|  | 2017 |  |  | 2016 |  |  | 2015 |
Future cash flows |  | $ | 4,451,665 |  |  | $ | 3,319,551 |  |  | $ | 4,097,568 |
Future production costs |  |  | (1,279,777 | ) |  |  | (1,054,211 | ) |  |  | (1,237,888 | )
Future development costs |  |  | (982,284 | ) |  |  | (829,926 | ) |  |  | (934,814 | )
Future income tax expense |  |  | (323,308 | ) |  |  | (132,834 | ) |  |  | (307,374 | )
Future net cash flows |  |  | 1,866,296 |  |  |  | 1,302,580 |  |  |  | 1,617,492 |
10% annual discount for estimated timing of cash flows |  |  | (1,405,265 | ) |  |  | (1,004,825 | ) |  |  | (1,157,097 | )
Standardized measure of discounted future net cash flows |  | $ | 461,031 |  |  | $ | 297,755 |  |  | $ | 460,395 |
Summary of 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 (in thousands):
|  | Years Ended December 31, |
|  | 2017 |  |  | 2016 |  |  | 2015 |
Balance, beginning of period |  | $ | 297,755 |  |  | $ | 460,395 |  |  | $ | 1,055,815 |
Net change in sales and transfer prices and in production (lifting) costs related to future production |  |  | 229,139 |  |  |  | (191,841 | ) |  |  | (1,405,864 | )
Changes in estimated future development costs |  |  | (72,439 | ) |  |  | 17,405 |  |  |  | 231,900 |
Sales and transfers of oil and gas produced during the period |  |  | (78,803 | ) |  |  | (62,835 | ) |  |  | (91,278 | )
Net change due to acquisition of minerals in place |  |  | 17,331 |  |  |  | — |  |  |  | — |
Net change due to extensions, discoveries and improved recovery |  |  | 49,377 |  |  |  | 13,988 |  |  |  | 156,783 |
Net change due to revisions in quantity estimates |  |  | (3,817 | ) |  |  | (25,236 | ) |  |  | (59,305 | )
Previously estimated development costs incurred during the period |  |  | 43,202 |  |  |  | 15,884 |  |  |  | 146,237 |
Accretion of discount |  |  | 30,789 |  |  |  | 46,040 |  |  |  | 105,582 |
Other |  |  | (1,677 | ) |  |  | (9,500 | ) |  |  | 6,915 |
Net change in income taxes |  |  | (49,826 | ) |  |  | 33,455 |  |  |  | 313,610 |
Standardized Measure of discounted future net cash flows |  | $ | 461,031 |  |  | $ | 297,755 |  |  | $ | 460,395 |

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- Definition Tabular disclosure of an enterprise's obligations to provide a fixed and determinable quantity of oil or gas in the near future under existing contracts or agreements. Information may include the principal sources of oil and gas to be relied upon and the total available amounts expected to be received from each principal source and from all sources combined; the total quantities of oil and gas which are subject to delivery commitments; and the steps taken to ensure available reserves and supplies are sufficient to meet such commitments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 1207 + Details
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