Document ID: EPA-HQ-OAR-2010-0505-4552
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2012-04-18T04:00Z

MEMORANDUM

DATE:	 	April 5, 2012

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SUBJECT:	NSPS Low Pressure Well Threshold: Summary and Impacts Estimates

In response to comments received on the proposed rule related to the technical infeasibility of gas capture from low pressure wells, the EPA evaluated alternative options and developed a pressure threshold in the final rule. This threshold is based on a simple equation operators can use to determine if the flowback pressure of a well is sufficient to overcome the pressure of the flow line, thus making gas capture through Reduced Emission Completions possible.  If the flowback gas of a well falls below the pressure threshold, combustion is allowed as an alternative.

Full details of the analysis to develop the pressure threshold and nation-wide impacts are available in the Determination of Minimum Flowback Pressure Memorandum. This document provides additional details on the impacts related to CBM wells

Further Details on the Low Pressure Threshold Impacts Analysis:

The data used in this analysis is 2008 data from HPDI, which contains detailed production and other related data on natural gas wells in the United States. Using this data set and other information to estimate the required equation input parameters, EPA applied the equation to each hydraulically fractured gas well completion in the data set to determine which completion would likely fall above or below the threshold. Based on this analysis, the key results are as follows:
   * 10% of hydraulically fractured wells nation-wide would fall below the pressure threshold in the rule and thus allowed to combust as an alternative to REC.
   * CBM represents about 85% of the total wells that are estimated to fall below the threshold; EPA's estimates show that the majority of CBM well completions in the dataset (almost 90%) would fall below the threshold.
CBM wells have been recognized by many commenters as having low VOC and should not be included in the rule. This analysis shows that even in the absence of a VOC threshold, the majority of these wells are likely not subject to the REC requirements.

Background: Overview of Final Rule Pressure Threshold Equation:

The final NSPS OOOO rule includes Equation 1 (below) for operators to determine if a well meets the threshold. Operators will input the reservoir pressure and vertical well depth (both of which are available at the time the well is perforated) for each gas well that is a hydraulic fracturing affected facility into Equation 1. This result of this equation will determine a calculated pressure of the gas immediately before it would be routed to the flow line, resulting in one of two cases: (1) the calculated line pressure is greater than the actual line pressure to be used by the operator, thus the gas capture using REC in combination with combustion is required, or (2) the calculated line pressure is less than or equal to the actual flow line pressure, combustion is allowed as an alternative. 

                         PL=0.445xPR-0.038xL+67.578
(Eq. 1)