# Presentation: 687382

## EIA’s Weekly Underground Natural Gas Storage Program

**Federal Energy Regulatory Commission**
**Technical Conference**
**September 28, 2004**
**Elizabeth Campbell**
**Energy Information Administration (EIA)**
***Elizabeth.Campbell@eia.doe.gov***

**www.eia.doe.gov**

## Overview of Presentation

- Survey respondents and sample
- Survey content
- Collection methods
- Estimation
- Release of estimates

## EIA Underground Natural Gas Storage Surveys—Weekly and Monthly

| Survey | Number of Respondents | Number of Fields | Volume Coverage |
| --- | --- | --- | --- |
| Weekly, EIA-912 | 56 | 292 | 91-96% by region |
| Monthly, EIA-191
 | 120 | 395 | 100% |

**Notes:**
Reporters to the weekly Form EIA-912 are companies that operate U.S. underground storage facilities who have been selected by EIA to be in the weekly survey sample.
The basis of the sample is the monthly storage survey (EIA-191) which provides a list of active underground storage fields.
The monthly census or sampling frame now includes 395 storage fields of 3 types operated by 120 reporting units.
Currently EIA receives weekly survey reports from 56 reporting units accounting for 292 fields.  
Note use of the terms “respondents or reporting units.”  Some companies have asked to report separately for a portion of their fields, usually by region depending on their company structure.  In other cases more than one respondent is reporting for a field, representing their share of that operation.  We accommodate both types of requests.
The sample provides from 91 to 96% coverage for the regions – about 92-93 % for U.S. at time of sample selection and as checked recently for June 2004.
EIA collects data from a sample rather than a census to reduce respondent burden associated with a weekly survey.  Under the Paperwork Reduction Act, OMB reviews each proposed survey of more than 9 respondents prior to approval to evaluate it under several criteria.  One is to minimize overall burden to U.S. citizens and businesses.  OMB expects the use of samples for surveys of higher frequency (weekly compared to monthly) whenever a reasonably stable sampling frame such as a monthly census survey exists.  They also review the sampling design to see that it is efficient.  This is the basis of the collection authority EIA has now.
 Some of the 395 fields may not have working gas at a specific point in time; reasons include preparing for sale of a field to a new owner since working gas may or may not be part of the sale, having withdrawn working gas at the end of winter heating season, or because of maintenance work.  

## Terms for Natural Gas in Storage 

**Base Gas:****  **The volume of gas needed as a permanent
- inventory to maintain adequate reservoir pressures and deliverability rates throughout the withdrawal season.

**Terms for Natural Gas in Storage **

**Source: *****EIA-912 Weekly Underground Natural Gas Storage Report  Instructions.***

**Notes:**

Working and base gas are defined as shown here.  Working gas changes throughout the year.  Base gas can change depending on reservoir conditions and equipment.  LNG in storage is out of scope for both the monthly and weekly surveys.

## Weekly Storage Report Regions

**Weekly Storage Report Regions**

**Notes:**

This map shows the 3 regions for which data are requested. 

## Weekly Underground Natural Gas Storage Report Form EIA-912

**Notes:**
The survey form is simple – it requests a weekly report of working gas inventory (in MMcf) held in all underground storage fields operated by a survey respondent for each of three regions of the U.S. as of 9 a.m. Friday morning.
EIA does not require respondents to measure working gas inventory with any specific technology or method.  EIA does not request any information on injections or withdrawals.  
We do not know what measurement methods respondents are using.  We understand they might include meters tracking flows into or out of the fields, analysis of pressure readings, or a combination.
On occasion some respondents have stated that they could not provide exact estimates of 9 a.m. inventories for some weekly report periods for a variety of reasons.  EIA has asked them to provide their best estimates in a timely fashion and to submit revisions, if necessary, when they have better information.

## Overview of Operations

- Working gas volumes as of 9:00 a.m. on Friday; due by COB Monday
- Respondents report company volumes at a regional level; estimates allowed
- EIA edits data; quality comparisons provided to monthly surveys
- EIA provides secure work areas for processing

**Notes:**
Data are received by email at a secure EIA data receipt website or by FAX.
Data are due by COB Monday.  We have about 2/3 of the respondents by the due date.  The remainder come in on Tuesday or Wednesday.
Follow-up and problem resolution for individual respondents occur by email and phone.  It is very useful to have alternative methods as it provides backup when one method is not working for either EIA or the respondent.
Data are edited by the system each week to compare new information to the respondent’s report history.  Data anomalies are then compared to trends in the region and the respondent’s history on the monthly survey.  Each month a comparison of the monthly and weekly data reports of the respondent units is done.  We provide a comparison of the weekly survey estimates and the monthly survey results for each month on the EIA website.  The average absolute error for the 26 months is 1.2 percent of working gas stocks.
The survey is mandatory and response rates have been excellent. The volume-weighted response rate at the time of first release for the last 6 months has been 98.6 percent.
EIA allows respondents to provide estimates if they are unable to provide a more precise measurement for a given week.  If a respondent has not reported for the week, an inventory value for that reporting unit is imputed by EIA.

## Revision Policy for Respondents

- Revised data should be submitted whenever the measure of working gas for the prior week in any region has been revised by 500 million cubic feet or more.
- Respondents are requested to submit a revised form when that happens

**Notes:**
Respondents submit revision for a prior report period when the measure of working gas for the prior week in any region has been revised by 500 million cubic feet or more.  If a respondent report was late for the prior week, the late report is entered also.

## Revision Policy for the EIA Weekly Natural Gas Storage Report (WNGSR)

**Revisions shall be disseminated in the WNGSR according to the established schedule and shall occur when the effect of reported changes is at least seven billion cubic feet at either a regional or national level.**** **
- If a revision is made, changes to all regions shall be recorded.
- Changes shall only lead to a published revision when it exceeds the seven billion cubic feet threshold.
- Revisions shall not be disseminated on an unscheduled basis.
- EIA will include revisions in the estimates as part of the next release of the *Weekly Natural Gas Storage Report* on its web site.

**Notes:**
Revisions to the estimates are posted for the prior report period whenever the value of the changes in one or more region is 7 Bcf or more.  Revisions are posted as part of the Thursday morning report.  Revisions are not posted between these periods.
The policy on the size and timing of revisions is the result of a public comment period initiated through a Federal Register notice in summer 2002.  The policy was documented in a November 12, 2002 FR notice and is accessible on the website.  The policy was based on comments that data users believed everyone should know exactly at what time a revision might be posted and also did not want the market to either freeze up or experience unnecessary volatility between the announcement of a coming revision and the appearance of the actual revision.

## Estimation Formula

**where:**
**Y = Estimate of working gas for a region**
**A = Estimation factor in the given region**
**wwg = Weekly working gas in storage for sample operators in region for the collection week**
**n = Number of operators in the estimation companies group**
**m = Number of operators in the base group; hence the total number of operators in the sample group equals n + m **
**K = Volumes of working gas that exhibited little or no variation at a company level, for companies in the nonsampled group**

**Notes:**
Estimates are calculated separately for each region each week.  The U.S. total estimate is the sum of the regional estimates.
In the method used for estimation since October 30, 2003, the estimate for the region consists of a part which is the product of an estimation factor times the sum of some respondents reports, a part which is simply the sum of other respondents reports, and a constant factor for the region.
Weekly respondents in each region were divided into the two groups depending on analysis of whether or not they were good candidates for representing nonsampled companies.  Those which were are in the group with the estimation factor.  
The implied net change in U.S. inventories is not collected on the survey.  It is the calculated difference between the inventory measures for the current week and the prior week.  For this reason, the implied net change will capture the impact of withdrawals, injections, reclassifications of gas reported to EIA, and any revisions in estimates for the prior period.

## Weekly Natural Gas Storage Report

**Notes:**
This is a view of part of the weekly storage report.  Estimates are prepared 52 weeks a year.  There are no weeks off and we have produced the report through snowstorms and a hurricane when other government offices were closed.
The weekly estimates are available for free on the EIA website, usually between 10:30 and 10:40 a.m. on Thursday. Changes to that schedule, such as when a government holiday occurs on Thursday, are shown in the official schedule on the website in advance and a note is included in the WNGSR itself from 1-2 weeks ahead of the affected date. 
EIA puts the current weekly storage inventory numbers in context by presenting a number of other data points.  These include inventory values for the previous week, for the comparable week a year before, and for a 5-year average for the comparable week.  The development of a 5-year average requires a historical weekly database.  EIA also does a percentage difference from the 5-year average.

## Weekly Natural Gas Storage Report

**Notes:**
The storage report includes the estimates and quantitative comparison information, a  paragraph of text, and a graph of weekly estimates against historical information. Other features are available by clicking on web-links.  These include the schedule, the historical time series in Excel format, methodology documentation, and a paper on storage industry basics.  
We do not provide any other discussion of the week’s numbers with this product because we are following, to the extent possible, the OMB guidelines for principal federal economic indicators.  Under these guidelines, statistical agencies must delay discussion of the data series just released beyond simple comparisons to the historical record or technical explanations for one hour after the release.
We have a policy about the use of “robot” dialup programs to access the site, which we periodically review to avoid unnecessary system load and to maintain operational integrity.  We have talked in the past with some customers about this issue as their robots can have the same effect as a hacker attack.
I hope this has been useful for understanding operational underpinnings of the weekly storage estimates.  I would be happy to answer questions.

## www.eia.doe.gov

**www.eia.doe.gov**

**www.eia.doe.gov**