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Informational Letter IL 92-5

To: All Oil and Gas Operators

26 March 1992

REDUCED FLUID SAMPLING AND ANALYSIS FOR HYDROCARBON MISCIBLE FLOOD SCHEMES

Background

Board approvals for miscible flood schemes have clauses outlining sampling and analysis requirements for determining produced solvent and chase-gas volumes. The requirements for progress reports are also specified in the approvals. There is a wide variation in the sampling and analysis practices, and in the contents of the progress reports. Many operators have questioned the need for liquid-phase samples and four applications have been filed to reduce or waive sampling requirements in certain pools. To resolve these matters and to avoid an ad hoc solution, Board staff met with all miscible flood operators in December 1991 and January 1992, and subsequently received written comments from six operators. This letter summarizes the changes to, and implementation of, Board policy as a result of these applications and meetings.

Findings

During the meetings, there was some debate respecting the purpose of the sampling and analysis program. Some operators said the program was designed to provide information for evaluating scheme performance (i.e. hydrocarbon conservation). Other operators said it could only be used to forecast future recovery of the injected solvent and chase gas (i.e. resource appraisal). In view of the different opinions, the Board reaffirms its historical position that the purpose of the program is to quantify produced volumes of solvent and chase gas on an individual-well basis and is primarily intended as a performance evaluation tool.

Most operators agreed that current liquid sampling requirements are unnecessary in the majority of pools and costly relative to the additional information obtained. Operators generally stated that reliable produced volumes could be determined from less costly gas sampling. Given the widespread nature of this opinion, the Board will delete liquid sampling requirements from the miscible flood approvals. However, in those few pools wherein some liquid sampling is required to validate the compositional analysis method, operators are requested to involve Board staff in deciding the locations and frequency of wells to be surveyed.

The Board received almost unanimous feedback from operators that sampling of representative wells is not a reasonable method for determining breakthrough volumes at individual wells. The Board agrees with this "all-or-nothing" approach and will, therefore, no longer accept representative producer-well sampling as its minimum requirement.

One of the Board's major concerns is that the methods used by operators to determine breakthrough volumes have not been properly documented for a majority of the ongoing schemes. This leads to confusion, uncertainty, and increased monitoring costs.

Gas Sampling Requirements for Producing Wells

Gas samples shall be taken and analyzed quarterly for all producing wells:

(a) during any period with simultaneous production of solvent and chase gas, where no other method is available for estimating breakthrough volumes of each fluid, and

(b) throughout the life of any scheme where the total breakthrough volume cannot be estimated by excess gas production (GOR method discussed next).

Situations where the GOR method may not be reliable include

• schemes with an initial gas cap,
• schemes with prior gas injection, or
• schemes with measurement difficulties.

Situations where the GOR method is most likely to be reliable include

• high-pressure, lean-gas schemes with continuous solvent injection and no chase-gas injection phase,
• the solvent injection phase in most schemes, or
• the late chase-gas injection phase where very little solvent (< 10% of the total breakthrough fluid stream) is being produced.

Fluid Sampling Requirements for Injection Wells

The Board will continue to require that injected solvent and chase gas be sampled and analyzed on a monthly basis. Operators should note that this information should now be submitted with progress reports rather than on a monthly basis.

Reporting Requirements

Progress reports must include

(a) either an explanation of the method being used to determine solvent and chase-gas breakthrough volumes and compositions, with a detailed example calculation, or a reference to a previous report that outlines the method,

(b) either monthly and cumulative volumes of produced solvent and chase gas on an individual-well and scheme basis, or the allocation factors used to calculate the breakthrough volumes,

(c) monthly and cumulative compositions of produced solvent and chase gas summarized on a scheme basis, and, where appropriate, this information could also be summarized on a pattern, area, stage, or phase basis, and

(d) monthly and cumulative compositions of injected solvent and chase gas summarized on a scheme basis.

Implementation

The Board is proceeding to grant requests to delete liquid sampling requirements in the Judy Creek Beaverhill Lake A and B Pools operated by Esso Resources Canada Limited (Application No. 900645), in the Pembina Nisku schemes operated by Esso Resources Canada Limited (Application No. 901033), and in the Mitsue Gilwood A Pool operated by Chevron Canada Resources (Application No. 910787). For Application No. 911273 by Chevron Canada Resources, requesting approval to discontinue oil and gas sampling requirements in its eight Nisku schemes in the Bigoray, Brazeau River, Pembina, and WestPem Fields, the Board has

• approved discontinuation of liquid sampling requirements in all eight schemes,
• approved discontinuation of gas sampling requirements in the four high-pressure lean-gas floods (Pembina Nisku A, WestPem Nisku A, C and D Pools), but has
• retained the requirement of gas sampling and analysis in the four rich "Slug" schemes (Brazeau River Nisku B, Bigoray Nisku F, and Pembina Nisku D and F Pools).

Over the past year, the Board has deferred a number of miscible flood approval amendments pending completion of the current review. The Board will now proceed to revise these approvals to be consistent with the updated sampling, analysis, and reporting requirements. The Board notes that, in the case of the Judy Creek Beaverhill Lake A and B Pools (operated by Esso), the Swan Hills South Beaverhill Lake A and B Pool (operated by Amoco), and the Nipisi Gilwood A Pool (operated by Amoco), discontinuation of the "representative" well option could substantially increase sampling costs. Therefore, the Board will not impose the stricter requirements in these four schemes at this time. Instead, Board staff will be contacting Esso and Amoco in the near future to discuss the need for continued sampling.

The Board believes that the revised requirements will result in significant savings for operators without jeopardizing the purpose or value of the data gathered. Any application to further reduce or modify sampling requirements will be considered by the Board on a case-by-case basis.

The Board appreciates the operators' help in responding to this sampling issue in a comprehensive and timely manner. Any questions, comments, or concerns should be directed to Tom Keelan (297-8549) or Barry Christensen (297-4102).

[Original signed by]

R. A. Purvis, P.Eng.
Manager
Oil Department