### Storage Vessel Applicability Determination and End of Flowback

Issue # 1: Inclusion of the word “maximum” in the average daily throughput toward estimating potential to emit (PTE) in the storage vessels applicability determination is problematic. The term “maximum average daily” in §60.5365(e) was promulgated in the September 23 , 2013 final rule revising NSPS, Subpart OOOO, referred to as the first reconsideration rule of NSPS OOOO (NSPS OOOO 1.0). This language was a significant departure from the proposal and it was not derived from any of the comments in response to the propo sal. API recommended 1 that the storage vessel emissions should be calculated “Using the first thirty days of production in a model to define PTE from a storage vessel, rather than requiring use of maximum design capacity to calculate PTE in a model or

req uiring use of enforceable operational limitations to cap PTE.” API made this recommendation based on the fact that production wells decline over the life of the well and production flow is highest immediately after the well is initially placed in productio n. A
30

- day average, beginning at the start of production, is most representative (and conservative due to production decline) while accommodating the fluctuations in flow that often occur due to the three phase (produced water, liquid hydrocarbons and na tural gas) flow in the well bore. Accurate measurement can only occur after separation of the three phases.

Recommendation #1 .1 : Remove “maximum” from §60.5365(e).

“The potential for VOC emissions must be calculated using a generally accepted model or calculation methodology, based on the maximum average daily throughput
determined for a 30

- day period of production prior to the applicable emission
determination deadl ine specified in this section.”

There are many generally accepted models and calculation methods to calculate a storage vessel’s PTE . One example of volume measurement is accomplished by:

1. strapping the liquid level at the opening and closing of the measure ment period (i.e.

, beginning and end of the month),
2. calculating the storage volumes from those two level measurements , 3. subtracting the opening volume from the closing volume, and
4. adding in any truck delivery tickets shipped from the vessel during that period.

API envisioned dividing the first 30 days of production reported by the number of days the well was flowing (to correct for any well shut

- ins that may have occurred due to o perational
constraints ). This would allow the operator to rely on data that is currently collected and easy for EPA to validate.

1 See API comments, May 28, 2013, Docket ID No. EPA

- HQ

- OAR

- 2010

- 0505 , page 38, first bullet.There are two major concerns with attempting to calculate a “maximum average daily”

production from short

- term flow measuremen ts . First, volume measurements for shorter periods of time are not as accurate as the accounting methods used to report production
volumes to state regulatory agencies

. Accounting volumes are used for the payment calculations for royalties, taxes, etc. a nd the accounting methods have been adjusted over the years for accuracy. Operators sometimes keep track of production volume over shorter periods of time to track the wells health and production progress, but these are not typically

correct ed for criteri a such as water content and temperature. The second major concern
when relying on short term measurements is the occurrence of peak and low flows caused by a variety of operational issues s uch as:

1. When the well is first placed in production, the well often surges high flow for a variable period of time. Production rates calculated during this period will exaggerate monthly production.
2. Throughout the production life, the collection of liquids in th e well bore can cause significant drops in production for a period of time, especially during the initial production period. Production rates calculated during this period will underestimate monthly production.

C alculating the daily average using the first 30 calendar day s of production and dividing it by the days the well was flowing is the most accurate determination of the initial production rate. This production rate is significantly higher than other times d uring the life of the well
, due to the rapid well depletion that occurs following initial well production.

Recommendation # 1. 2 : EPA should not further specify what data is required to calculate the potential for VOC emissions as required by 60.5365(e). The data needed to calculate emissions is intimately link ed to the “generally accepted model or calculation methodology” selected to calculate the emissions. The data sampling and gathering protocols must match
the model for the calculation to be accura te. Any attempt to specify what data must be
collected and how that data is to be obtained would necessarily restrict which models or
calculation met hodology could be used. In t he “Response to Public Comments on Proposed Rule August 23, 2011 (76 FR 52738 )” on page 125 , EPA recognizes that restricting the methodologies used to calculate emissions would be both difficult and limit the use of new methodologies :

“ Response: We disagree that the EPA should specify which methodologies must be used to calculate VOC emissions. Different methodologies may be more appropriate than others for certain situations, and it would be very difficult to determine each possible situation an d determine the appropriate methodology for that situation. Additionally, such a prescriptive requirement would not allow as yet undeveloped methodologies to be used, or would require amending the rule whenever a newmethodology was released. For these rea sons, the final rule specifies that any

generally accepted methodology may be used to estimate emissions.”

Specifying what data must be collected and how that data is to be collected would sever e ly limit the “generally accepted methodology” that could be used. For example, specifying that a crude or condensate sample must be taken using a defined protocol would essentially prohibit the direct measurement of tank emissions.

Issue #2: API has recommended in previous discussions with EPA that the end of flo wback

can , in most cases
, be visibly determined by a non

- industry observer by what is happening at the well site surface. In our recommendations we have suggested that Subpart OOOO could stipulate that end of flowback occurs when a well is shut

- in and dis connected from flowback equipment, and flowback crews have left the site after being released. Any well flow that begins subsequent to observations indicating the end of flowback would be considered production. Examples of equipment onsite during flowback that will not typically
be observed when in production are:

 Temporary flowlines tied into the well put together by hammer unions and laid along the ground to flowback equipment and tankage.

 Temporary piping with hammer unions connecting separators, tankage, and
combustion device

.

 A skid mounted choke manifold used to regulate flowback and divert flow as
needed

.

 Portable separators to separate produced fluids and solids

.

 A portable flowback combustion device or flare

.

 Portable tankage such as a frac t ank.

When a well is put into production, the temporary flowlines, with hammer unions, connecting flowback equipment are typically removed and replaced with permanent threaded, flanged, or welded piping connecting the well to the permanent production equip ment such as heater treaters, separators, or collection system. The permanent flowlines are often buried, but in some cases are above ground laid on pipe racks. The presence of a flowback crew is the best indicator of being in flowback and not production
mode i n the rare instances where some of the above equipment continues to be used during initial production or where production facilities constructed previously are used for
flowback.

Recommendation # 2 : Use the examples provided above in the preamble of the final rule amendments to clarify the equipment changes when flowback ends and production begins to simplify the final rule requirements.