Exhibit 10.13

ASSIGNMENT

FOR AND IN CONSIDERATION for the payment by TURBECO, INC. (the “Buyer”) of a
purchase price of $12,500,000.00, B. L. PEREZ (the “Seller”) hereby assigns,
transfers, and conveys to the Buyer, all of his right, title, and interest with
respect to his membership interest in CAVO DRILLING MOTORS LTD., CO., a Texas
limited liability company (the “Company”).

The Seller hereby agrees to deliver to Buyer from time to time after closing any
documents or instruments necessary to vest in Buyer the ownership of the
membership interest in the Company assigned hereby, and/or to vest in the
Company ownership to its assets.

This Agreement constitutes the sole agreement of the parties with respect to the
subject matter and supersedes any prior understandings or written or oral
agreements between the parties respecting that subject matter.

IN WITNESS WHEREOF, the undersigned have executed this assignment on
November 15, 2007, to be effective as of November 1, 2007.

 

SELLER:

/s/ B. L. Perez

B. L. Perez

Accepted:

 

TURBECO, INC. By:  

/s/ Lisa Meier

  Lisa Meier, Chief Financial Officer