EOG's Huff and Puff

The following is provided by the The Rocky Mountain Oil Journal:

EOG Plans CO2 Huff N’ Puff Pilot Program In Parshall Field-Mountrail County North Dakota

Realizing that the flush production associated with the recently drilled wells in the Greater Parshall Field area will decline, EOG Resources (EOG), the largest producer within this field, is planning to initiate a CO2 Huff n’ Puff pilot program to determine the best method to recover as much oil as possible from the horizontal Bakken.

The company has requested from the North Dakota Industrial Commission an order granting authority to recomplete and use the Austin #1-02H well, located in the sw-se 2-154n-90w Mountrail County, ND, as a combined production/injection well for a Huff n’ Puff CO2 operation in the Parshall-Bakken Pool for an injectivity test period of up to three months; authorizing the flaring and/or venting of the waste gas produced from the well during the test period and such other relief as is appropriate. At the present, there is no Bakken well within the state that is employing this method for additional oil recovery.

The Austin #1-02H test well was completed in the latter part of 2007 for an IPF of 781 bopd, 285 mcfgpd and 29 bwpd from a single lateral leg interval 9,484’-14,435’. At the time of this completion, this producer extended the northern portion of Parshall Field by about nine miles. Cumulative production for this hole is 188,035 bo, 59.7 mmcfg and 3,925 bw. Since the completion of the #1-02H, EOG has drilled 18 more horizontal Bakken wells in this township with at least 12 more locations to drill.

Although the particulars of this huff-n-puff pilot program has yet to be revealed, the general concept includes the following:

What is it?

The name is derived from the children's story of the big bad wolf in Little Red Riding Hood. It was first applied to cyclic steam injection. The CO2 Huff n' Puff is the injection of carbon dioxide into a producing oil well (huff), followed by a production period when the well is flowed back (puff). This process can be repeated as often as deemed necessary.

How does it work?

• Some or all of the following mechanisms aid in the stimulation of oil production by the CO2 Huff n' Puff:
• Oil swelling, thereby reducing its viscosity and increasing its flow rate to the wellbore.
• Solution gas drive is imparted by the CO2 from its dissolving in the oil.
• Increase in relative permeability to oil by decreasing the interfacial tension. CO2 will quickly saturate formation water and displace it from the near wellbore area. This typically results in lower water production in the "Puff" part of the treatment.
• Vaporization of light crude ends and recovery of same from produced CO2 gas.
• Entrapment of CO2 gas by gas hysteresis- CO2 is trapped in the H&P zone preventing the H&P zone from being re-saturated by the oil coming from further out in the reservoir.

What is a typical CO2 Huff n' Puff candidate?

• The process is not lithology dependant- it can be applied to either sandstones or carbonates.
• It is most successful when pumped into pressure depleted reservoirs. Average CO2 utilization in a 65 well test in an Applachian reservoir with about 100 psi BHP was .97 mscf/bbl. of incremental oil.
• Wells in faulted or lenticular reservoirs where inter-well communication often does not occur are good candidates.
• A well that has been a good primary producer, that still has a high residual oil saturation, but may be pressure depleted.

Content courtesy of The Rocky Mountain Oil Journal