Magnolia also brought online a 2-well pad located approximately 20 miles outside the initial core area and were expected to be gassier than the average Giddings well in the core area. These wells had a 90-day average production rate of 543 Bbl/d of oil and 7.3 MMcf/d of natural gas per well, which were ahead of our expectations.
Updated Guidance
For 2021, Magnolia expects to spend approximately 50% to 60% of our adjusted EBITDAX for drilling and completing wells, which is consistent with our business model. Should product prices remain at current levels, we estimate our capital spending to be in the lower half of the expected range. The 2021 activity plan consists of operating a one rig program at Giddings, drilling multi-well pads primarily in our initial core area. In the Karnes area, we plan to complete 10 drilled but uncompleted wells (“DUCs”), most of which should be brought online during the first half of the year. Non-operated activity at Karnes is expected to increase compared to the 2020 levels. Our 2021 capital and activity plan is expected to deliver mid-single digit production growth on a year-over-year basis.
Looking at the first quarter of 2021, D&C capital should be approximately 50% of our adjusted EBITDAX, at elevated product prices. Operated activity will continue to focus on Giddings and, we expect to begin completing some of the Karnes DUCs in the latter part of the quarter. Production in the first quarter of 2021 is forecast to be relatively flat compared to fourth quarter levels, which incorporates a rough estimate of recent cold weather-related outages in the field. Oil price differentials are anticipated to be roughly a $3 per barrel discount to Magellan East Houston (“MEH”) during the first quarter.
2020 Oil and Gas Reserves Replacement and F&D Costs
Magnolia’s total proved developed reserves at year-end 2020 were 85.8 MMboe. The company added 30.4 MMboe of proved developed reserves during the year, excluding acquisitions and price related revisions and replacing 135% of 2020 production. Total costs incurred excluding property acquisition costs, exploration costs and asset retirement obligation costs were $194.9 million in 2020 resulting in organic proved developed F&D costs of $6.41 per boe.
Total 2020 proved reserves increased to 112.3 MMboe from 109.3 MMboe at year end 2019 and replaced 113% of 2020 production. Magnolia books only one year of proved undeveloped reserves and as a result, 76% of its 2020 proved reserves were developed.
Annual Report on Form 10-K
Magnolia's financial statements and related footnotes will be available in its Annual Report on Form 10-K for the year ended December 31, 2020, which is expected to be filed with the U.S. Securities and Exchange Commission (“SEC”) on February 23, 2021.
Conference Call and Webcast
Magnolia will host an investor conference call on Tuesday, February 23, 2021 at 10:00 a.m. Central (11:00 a.m. Eastern) to discuss these operating and financial results. Interested parties may join the webcast by visiting Magnolia's website at www.magnoliaoilgas.com/investors/events-and-presentations and clicking on the webcast link or by dialing 1-844-701-1059. A replay of the webcast will be posted on Magnolia's website following completion of the call.
About Magnolia Oil & Gas Corporation
Magnolia (MGY) is a publicly traded oil and gas exploration and production company with operations primarily in South Texas in the core of the Eagle Ford Shale and Austin Chalk formations. Magnolia focuses on generating value for shareholders through steady production growth, strong pre-tax margins, and free cash flow. For more information, visit www.magnoliaoilgas.com.
Cautionary Note Regarding Forward-Looking Statements
The information in this press release includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements, other than statements of present or historical fact included in this press release, regarding Magnolia’s strategy, future operations, financial position, estimated revenues and losses, projected costs, prospects, plans and objectives of management are forward looking statements. When used in this press release, the words could, should, will, may, believe, anticipate, intend, estimate, expect, project, the negative of such terms and other similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain such identifying words. These forward-looking statements are based on management’s current expectations and assumptions about future events and are based on currently available information as to the outcome and timing of future events. Except as otherwise required by applicable law, Magnolia disclaims any duty to update any forward-looking statements, all of which are expressly qualified by the statements in this section, to reflect events or circumstances after the date of this press release. Magnolia cautions you that these forward-looking statements are subject to all of the risks and uncertainties, most of which are difficult to predict and many of which are beyond the control of Magnolia, incident to the development, production, gathering and sale of oil, natural gas and natural gas liquids. In addition, Magnolia cautions you that the forward looking statements contained in this press release are subject to the following factors: (i) the length, scope and severity of the ongoing coronavirus disease 2019 (“COVID-19”) pandemic, including the effects of related public health concerns and the impact of continued actions taken by governmental authorities and other third parties in response to the pandemic and its impact on commodity prices, supply and demand considerations, and storage capacity; (ii) the outcome of any legal proceedings that may be instituted against Magnolia; (iii) Magnolia’s ability to realize the anticipated benefits of its acquisitions, which may be affected by, among other things, competition and the ability of Magnolia to grow and manage growth profitably; (iv) changes in applicable laws or regulations; and (v) the possibility that Magnolia may be adversely