Document:

<PAGE>   1
                                                                   EXHIBIT 10.31

                             DEBT PURCHASE AGREEMENT

                  This Agreement ("Agreement") is entered into as of August 1,
2001, by and between NATIONAL ENERGY GROUP, INC., a Delaware corporation
("Purchaser"), and HIGH COAST LIMITED PARTNERSHIP, a Delaware limited
partnership ("Seller").

                  WHEREAS, Seller desires to redeem with Purchaser by selling to
Purchaser $8,363,000 in face amount of 10-3/4% notes due November 1, 2006 of
National Energy Corp., together with interest thereon accrued through August 1,
2001 (the "Debt") and Purchaser desires to redeem the Debt by purchasing the
Debt from Seller, subject to the provisions contained herein.

                  NOW, THEREFORE, in consideration of the mutual promises and
covenants contained in this Agreement, and intending to be legally bound by the
terms and conditions of this Agreement, the parties hereto hereby agree as
follows:

         1. Sale of Debt to Purchaser.

                  1.1. Sale and Purchase of Debt. Subject to the terms and
conditions of this Agreement, Seller hereby sells, assigns and delivers to
Purchaser and Purchaser hereby purchases from Seller, the Debt for an aggregate
purchase price of $5,59l,229.78 in cash (the "Purchase Price"), to be payable by
Purchaser to Seller via electronic wire transfer in immediately available funds
to the account of Seller in accordance with the wire instructions to be provided
by Seller to Purchaser contemporaneously with the delivery of the Debt.

         2. Representations and Warranties of Seller. In connection with the
purchase of the Debt, Seller hereby represents and warrants to Purchaser as
follows:

                  2.1. Title to Debt. Seller has good legal title to the Debt,
and has the full legal right, power and authority to sell, assign and transfer
complete ownership in the Debt to Purchaser, free and clear of all liens,
claims, restrictions, encumbrances, charges, options or rights of third parties
with respect thereto.

                  2.2. Brokers. No broker, finder or investment banker is
entitled to any brokerage, finder's or other fee or commission in connection
with the transactions contemplated by this Agreement based upon any arrangement
made by or on behalf of Seller.

                                       1

<PAGE>   2

         3. Representations and Warranties of Purchaser.

                  Purchaser represents and warrants to Seller as follows:

                  3.1. Brokers. No broker, finder or investment banker is
entitled to any brokerage, finder's or other fee or commission in connection
with the transactions contemplated by this Agreement based upon any arrangement
made by or on behalf of Purchaser.

         4. Indemnity.

                  4.1. Purchaser shall defend, indemnify and save and hold
harmless Seller from and against all liabilities, losses, claims, demands,
suits, costs, expenses and damages of every kind and character, including,
without limitation, attorneys' fees, court costs, and costs of investigation,
which arise from or in connection with in any way a breach by Purchaser of its
representations and warranties contained in this Agreement or other breach of
this Agreement by Purchaser.

                  4.2. Seller shall defend, indemnify and save and hold harmless
Purchaser from and against all liabilities, losses, claims, demands, suits,
costs, expenses and damages of every kind and character, including, without
limitation, attorneys' fees, court costs, and costs of investigation, which
arise from or in connection with in any way a breach by Seller of its
representations and warranties contained in this Agreement or other breach of
this Agreement by Seller.

         5. Miscellaneous.

                  5.1. Assignment; Successors and Assigns. The provisions of
this Agreement shall be binding upon, and inure to the benefit of, the
respective successors, assigns, heirs, executors and administrators of the
parties hereto.

                  5.2. Survival of Representations and Warranties. All
indemnities, covenants, representations and warranties contained herein shall
survive the execution and delivery of this Agreement and the Closing of the
transactions contemplated hereby.

                  5.3. Expenses. Each party to this Agreement shall bear its own
costs and expenses, including, but not limited to, attorneys' fees and expenses,
in connection with the closing of the transactions contemplated hereby.

                  5.4. Notices. All notices, requests, consents and other
communications under this Agreement shall be in writing and shall

                                       2
<PAGE>   3

be delivered by hand, by telecopier, by overnight mail or mailed by first class
certified or registered mail, return receipt requested, postage prepaid. Notices
provided in accordance with this Section 5.4 shall be deemed delivered upon
personal delivery, receipt by telecopy or overnight mail, or 48 hours after
deposit in the mail in accordance with the above.

                  5.5. Entire Agreement. This Agreement, together with the
instruments and other documents contemplated to be executed and delivered in
connection herewith, contains the entire agreement and understanding of the
parties hereto, and supersedes any prior agreements or understandings between or
among them, with respect to the subject matter hereof.

                  5.6. Amendments and Waivers. This Agreement may not be amended
or waived (either generally or in a particular instance and either retroactively
or prospectively) except by a written instrument signed by the party against
whom enforcement of such amendment, modification or waiver is sought. No waivers
of or exceptions to any term, condition or provision of this Agreement, in any
one or more instances, shall be deemed to be, or construed as, a further or
continuing waiver of any such term, condition or provision.

                  5.7. Counterparts. This Agreement may be executed in several
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                  5.8. Captions. The captions of the sections, subsections and
paragraphs of this Agreement have been added for convenience only and shall not
be deemed to be a part of this Agreement.

                  5.9. Governing Law. This Agreement shall be governed by and
interpreted and construed in accordance with the laws of the State of New York.

                  5.10 Further Assurances. Seller and Purchaser hereby agrees to
take such further action and execute and deliver such further documents and
instruments as may be necessary or appropriate to perfect the transactions,
assignments, transfers and conveyances contemplated in the Agreement.

                            [signature page follows]

                                       3
<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have executed and delivered
this Agreement as an instrument as of the date first above written.

                                               NATIONAL ENERGY GROUP, INC.

                                               By: /s/ BOB ALEXANDER
                                                  ------------------------------
                                                  Name: Bob Alexander
                                                       -------------------------
                                                  Title: President
                                                        ------------------------

                                               HIGH COAST LIMITED PARTNERSHIP
                                               BECKTON CORP., General Partner

                                               By: /s/ EDWARD E. MATTNER
                                                  ------------------------------
                                                  Name:  Edward E. Mattner
                                                  Title: Authorized Signatory

                   [Signature Page to Debt Purchase Agreement]

                                       4<PAGE>   1

                                                                    Exhibit 10.1

                     FIRST AMENDMENT TO EMPLOYMENT AGREEMENT

        THIS FIRST AMENDMENT TO EMPLOYMENT AGREEMENT is made and entered into as
of May 8, 2001, by and between by and between AVIDYN, Inc., a Delaware
corporation (the "Corporation"), and Joseph A. Hensley ("Employee").

                                 WITNESSETH:

        WHEREAS, the Corporation and Employee have entered into that certain
Employment Agreement dated March 5, 2001 (the "Agreement");

        WHEREAS, certain misstatements were made the Agreement and his bonus for
2001 has been set;

        NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained and other good and valuable consideration hereinafter recited,
the Corporation and Employee agree as follows:

        1. BONUS. The first sentence of Section 4(b) shall read in its entirety
as follows: "Employee will receive a bonus for calendar year 2001 of one and
one-half percent (1 1/2%) of the Corporation's operating income for the twelve
months ended December 31, 2001."

        2. OPTIONS. The second sentence of Section 4(c) shall read in its
entirety as follows: "Such options will vest at the rate of twenty percent (20%)
per year for five (5) years except that the vesting will accelerate (if not
already vested) as to 12,500, 25,000, 37,500 and 50,000 options in the event the
trading price reaches $7.19, $8.63, $10.06 and $11.50, respectively, as defined
in the stock option agreement."

        3. BINDING EFFECT. The Agreement is hereby ratified and confirmed and
shall remain and continue in full force and effect in accordance with its
original terms and provisions, except as specifically amended hereby.

        4. COUNTERPARTS. This Amendment may be executed in one or more
counterparts, each of which shall be deemed an original and all of which shall
constitute one document.

        5. CONFLICT OF LAWS. The laws of the State of Texas shall govern this
Amendment without giving effect to its conflict of law provisions.

        IN WITNESS WHEREOF, the parties have executed this First Amendment to
Employment Agreement as of the date first written above.

                                   AVIDYN, Inc.

                                   By:    /s/ J. Ward Hunt
                                      ---------------------------------
                                      J. Ward Hunt, Chairman of the Board

                                          /s/ Joseph A. Hensley
                                   ------------------------------------
                                   Joseph A. Hensley

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00028-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00028-of-00352.parquet"}]]