Abstract

Ten percent of Alberta's gas reserve is associated with low quality reservoirs known as the Milk River, Medicine Hat, and Second White Specks formations. Although the quality of the reservoirs is low the quantity of production information has has its own quality which provides confidence in historical type curves. These curves have been interpreted to describe the various productive characteristics of remaining reserve and available producability.

Using the most recent information on productive rate, the cumulative production and the time oil production, two methods of type curve analysis will be compared. The problem of scaling the type curves to field measurements boils down to two equations in three variables. Our faith in our ability to plot a representative type curve provides the compatibility necessary to accomplish a meaningful scaling exercise.

The first method will be dealt with briefly and outlines a graphical procedure which interpolates the relationship between the current rate and the initial tested rate of the well to determine the reserve associated for the well and field.

The second and preferred method is more rigorously numerical. It involves averaging rate and cumulative derived indexes which provide a direct scaling factor for initial rare Will ultimate reserve.

Direct comparison of the the two methods is provided at the hypothetical and practical levels using actual field data. The various characteristics for each formation are tabled and Gil example of a computer spreadsheet is incorporated.

Introduction

The quality of a shallow gas well is typically described in terms of its current rate, the volume produced and how old the well is. If this were the only reliable information available, determining the effectiveness of field improvements from sweet spots in the field would be a difficult and time consuming chore. Precise determination of shallow gas reserve has only limited practical application, since individual circumstances raise questions of whether a wells performance is related lo completion, well specific circumstance, or field management. This empirically consistent method will improve the grading characteristics for performance and rate projections. The following procedure has merit regarding the repeat able prediction of reserves and consequently the well's short term and ultimate producability. Comparisons of varying field management standards can then be achieved from the start point of reasonable ultimate reserves expectations.

This procedure has broad use for the practical scaling of reserves on a well by well and field basis. It can also assist with consistency of production forecasting. The procedure is well suited to implementation through a simple spreadsheet which allows the summation of multiple wells and well groupings towards facility oplimiz3tion.

The traditional method of type Curve analysis incorporates some type or initial rate testing and then relates the initial rate lo the Warren curves. (The curves contained in the paper titled Southeastern Alberta Shallow Gas Pools Reserves and Performance Data by Andy Warren, Energy Resources Conservation Board). When inconsistencies are experienced, questions regarding the quality of the initial test procedures and other data are raised. Since the initial testing is characteristically reflective or the operator in terms of consistency, the reserve estimates arc deemed to be approximate.

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