لخّصلي

One of the fundamental principles utilized in engineering work is the law of conservation of matter.If one uses the straight-line method, then plotting and analysis are musts.The straight-line method was first recognized by van Everdingen, et al,' but for some reason, it was never fully exploited.The advantages and the elegance of this method can be more appreciated after a few cases are carefully treated and worked out by it.

One of the fundamental principles utilized in engineering work is the law of
conservation of matter. The application of this principle to hydrocarbon
reservoirs for quantitative deductions and prediction is termed "the material
balance method of reservoir analysis". While the construction of the material
balance equation (MBE)and the computations that go with its application are
difficult tasks, the criteria that a successful solution of the MBE should fulfill
have always been a problem facing the reservoir engineer.
True and complete criteria should embody necessary and sufficient conditions. The
criteria that the reservoir engineer uses possess a few necessary but not sufficient
conditions. Because of this, the answers obtained from the MBE are always open to
question. However, the degree of their acceptability should increase with the
increase in the number of the necessary conditions that they should satisfy.
Generally, the necessary conditions commonly used are (1) unspecified consistency
of the results and (2) the agreement between the MBE results and those
determined volumetrically.
This second criterion is usually overemphasized. The volumetrically determined
results are based on geological and petrophysical data of unknown accuracy.
In addition, the oil-in-place obtained by the MBE is the oil that contributes to the
pressure-production history, while the volumetrically calculated oil-in-place refers
to the total oil, part of which may not contribute to said history. Because of this
difference, the disagreement between the two answers might be of paramount
importance, and the concordance between them should not be overemphasized as
the measure of the correctness of either one. In this paper, a third necessary
condition of mathematical as well as physical significance is discussed. It isn't
subject to any geological or petrophysical interpretation, and as such, it is probably
the most important necessary condition. It consists essentially of rearranging the
MBE to result in an equation of the straight line. This straight-line method of the
MBE solution has invalidated a few long-time accepted concepts. For instance, it
has always been advocated that if a water drive exists, but one neglects to take it
into account in the MBE, the calculated oil-in-place should increase with time. The
straight-line method shows that in some cases, depending on the size of the
neglected aquifer, the calculated oil-in-place might decrease with time.
The straight-line method requires the plotting of the available group and another
variable group, with the variable group selection depending on the mechanism of
production under which the reservoir is producing. The most important aspect of
this method of solution is that it attaches significance to the sequence of the
plotted points, the direction in which they plot, and the shape of the resulting plot.
Thus, a dynamic meaning has been introduced into the picture in arriving at the
final answer. Since the emphasis of this method is placed on the interpretation of
the sequence of the points and the shape of the plot, one cannot completely
automate the whole sequence to obtain "the best value" as normally done in the
routine application of the MBE. If one uses the straight-line method, then plotting
and analysis are musts.
The straight-line method was first recognized by van Everdingen, et al,' but for
some reason, it was never fully exploited. The advantages and the elegance of this
method can be more appreciated after a few cases are carefully treated and
worked out by it.