SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 7)*

Access Midstream Partners, L.P.

(Name of Issuer)

Common Units Representing Limited Partner Interests, No Par Value

(Title of Class of Securities)

00434L109

(CUSIP Number)

Global Infrastructure Investors II, LLC

Attention: Joseph Blum

12 East 49th Street

New York, New York 10017

(212) 315-8100

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

March 14, 2014

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See § 240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

This Amendment No. 7 to Schedule 13D (“Amendment No. 7”) amends the Schedule 13D filed with the Securities and Exchange Commission on June 25, 2012, as previously amended (the “Schedule 13D”), relating to the Common Units representing limited partner interests (the “Common Units”) of Access Midstream Partners, L.P., a Delaware limited partnership (the “Issuer”) by each of the following persons (each a “Reporting Person” and collectively the “Reporting Persons”): Global Infrastructure Investors II, LLC (“Global Investors”), Global Infrastructure GP II, L.P. (“Global GP”), GIP II Eagle Acquisition Holdings GP, LLC (“Eagle GP”), GIP II Eagle Holdings Partnership, L.P. (“Eagle Holdings”), GIP II Hawk Holdings Partnership GP, LLC (“Hawk GP”), GIP II Hawk Holdings Partnership, L.P. (“GIP II-Hawk”), GIP II Eagle 2 Holding, L.P. (“Eagle 2”) and GIP II Hawk 2 Holding, L.P. (“Hawk 2”). Capitalized terms used herein without definition shall have the meanings set forth in the Schedule 13D.

Item 4 is hereby amended and supplemented by the following:

Access Midstream Ventures, L.L.C. (“AMV”) is the sole member of the Issuer’s general partner, Access Midstream Partners GP, L.L.C. (the “General Partner”), and has the right to appoint the General Partner’s entire board of directors (the “Board”). Pursuant to their direct and indirect ownership in AMV, certain of the Reporting Persons have the right to designate certain members to the board of managers of AMV and to the Board. The current designees to the Board by certain of the Reporting Persons include William J. Brilliant, James J. Cleary and William A. Woodburn, each of whom is an employee of Global Infrastructure Management, LLC. The current designees to the board of managers of AMV by certain of the Reporting Persons include Mr. Brilliant and Mr. Woodburn.

Effective February 19, 2014, pursuant to the terms of the First Amended and Restated Agreement of Limited Partnership of Access Midstream Partners, L.P., dated as of August 3, 2010 (as amended, the “Partnership Agreement”), GIP II-Hawk and Hawk 2 elected to convert 5,335,317 and 264,317 Subordinated Class C units (the “Class C Units”), respectively, into Common Units on a one-for-one basis (the “Conversion”) as provided in the Partnership Agreement.

On March 14, 2014, Eagle Holdings and Eagle 2 sold an aggregate of 9,200,000 Common Units to Barclays Capital Inc. (the “Underwriter”) at a price of $54.53 per Common Unit, in a registered offering (the “Secondary Offering”) pursuant to an Underwriting Agreement, dated as of March 11, 2014 (the “Underwriting Agreement”), by and among the General Partner, the Issuer, Access MLP Operating, L.L.C., Eagle Holdings, Eagle 2 and the Underwriter. The amount of Common Units sold in the Secondary Offering includes 1,200,000 Common Units which were sold pursuant to the exercise of the Underwriter’s overallotment option on March 11, 2014.

Pursuant to the Underwriting Agreement, Eagle Holdings and Eagle 2 have entered into lock-up agreements (the “Lock-up Agreements”) pursuant to which each of them have agreed with the Underwriter not to dispose of or hedge any Common Units or securities convertible into or exchangeable for Common Units during the period from March 11, 2014 continuing through and including the date 45 days after March 11, 2014, except with the prior written consent of the Underwriter.

The foregoing descriptions of the Underwriting Agreement and the Lock-up Agreements do not purport to be complete and are qualified in their entirety by reference to the Underwriting Agreement, which is filed as Exhibit 2 hereto, and the form of Lock-up Agreement, which is included as Exhibit F to the Underwriting Agreement, and are incorporated herein by reference.

Except as set forth above in this Item 4, as amended and supplemented, the Reporting Persons and Related Persons have no present plans or proposals which would result in or relate to any of the transactions described in subparagraphs (a) through (j) of Item 4 of Schedule 13D.

Item 5 is hereby amended and restated by the following:

(a) – (b)

The following sets forth, as of the date of this Schedule 13D, the aggregate number and percentage of Common Units beneficially owned by each of the Reporting Persons, as well as the number of Common Units as to which each Reporting Person has the sole power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition of.

Eagle Holdings holds 42,429,970 Common Units. Eagle GP is the general partner of Eagle Holdings and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by Eagle Holdings.

GIP II-Hawk holds 5,335,317 Common Units and 5,980,388 Class B Units. Hawk GP is the general partner of GIP II-Hawk and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by GIP II-Hawk.

Global GP is the managing member of each of Eagle GP and Hawk GP and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by Eagle GP and Hawk GP.

Eagle 2 holds 712,757 Common Units. Global GP is the general partner of the managing member of the general partner of Eagle 2 and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by Eagle 2.

Hawk 2 holds 264,317 Common Units and 296,273 Class B Units. Global GP is the general partner of the managing member of the general partner of Hawk 2 and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by Hawk 2.

Global Investors is the sole general partner of Global GP and, in such capacity, may be deemed to share beneficial ownership of the Common Units beneficially held by Global GP.

Eagle Holdings, Eagle GP, Eagle 2, GIP II-Hawk, Hawk GP, Hawk 2, Global GP and Global Investors may be deemed to be acting as a group in relation to their respective holdings in the Issuer but do not affirm the existence of any such group.

Except as set forth in this Item 5(a)-(b), each of the persons named in this Item 5(a)-(b) disclaims beneficial ownership of any Common Units owned beneficially or of record by any other person named in this Item 5(a)-(b).

(c) Item 4 above summarizes the Conversion and the Secondary Offering and is incorporated herein by reference.

Except for the Conversion and the Secondary Offering, none of the Reporting Persons or Related Persons has effected any transactions in the Common Units, the Class B Units or the Class C Units in the past sixty days.

(d) None.

(e) Not applicable.

Item 6 is hereby amended and supplemented by the following:

Item 4 above summarizes certain provisions of the Underwriting Agreement and the Lock-up Agreements and is incorporated herein by reference. A copy of the Underwriting Agreement, which includes the form of Lock-up Agreement as Exhibit F thereto, is attached as Exhibit 2 to this Amendment No. 7, and is incorporated by reference herein.

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: March 19, 2014