Introduction In the past, other authors have studied the influence of a skin effect on the productivity of a well. This skin effect, expressed by the skin factor S, is considered to be caused by a thin layer of impaired permeability immediately around the wellbore and extending vertically over the whole productive interval penetrated by the well. The skin factor S is defined as follows. Based on this, the impairment in productivity caused by a skin can be expressed by the fractional loss in productivity I, which is the loss in productivity divided by the total unimpaired productivity. Statement of Problem The present paper deals with a different kind of productivity impairment. Consider a well in which part of the productive formation is blocked off completely, either by incomplete penetration or by exclusion of parts of the productive zone by blank casing. In Fig. 1 (A, B and C), three examples are shown. Fig. 1(A) shows the situation where a well only partially penetrates the formation. This often is done to combat the actual or imagined danger of bottom-water coning. Fig. 1(B) shows a well producing from only the central portion of a productive interval. This type of completion is sometimes used where both water and gas coning are a problem. Although the case of a well producing through perforated casing cannot be treated in a manner similar to the previous two cases (where radial flow in the horizontal plane is assumed), Fig. 1(C) shows several intervals open to production and qualitatively describes this case (as will be discussed later).
Published in Petroleum Transactions, AIME, Volume 201, 1954, pages 182–191. Abstract A method has been developed for calculating the average pressure in a bounded reservoir. The reservoir is first divided into the individual drainage volumes of each well, by using the criterion that at steady state each individual drainage volume is proportional to a well's production rate. The average pressure in each drainage volume is then calculated by a method developed in the report. By volumetrically averaging these individual drainage volume pressures, the average pressure in the entire reservoir is obtained. To calculate the average pressure in each drainage volume, a correction is applied to the ordinary extrapolated pressure, i.e., the pressure obtained by extrapolating to infinite time the linear portion of the graph of closed-in pressure versus log [?t/(t + ?t)], where ?t is the closed-in time and t the production time. The correction, which is a function of the production time, is presented in graphical form for different shapes of the drainage area (horizontal cross section of the drainage volume). Introduction It is important to be able to find the volumetric average pressure in a reservoir so that the size of the reservoir may be determined from material balance calculations. It is also desirable to be able to find the approximate distribution of pressure within a reservoir for detection of fluid movement. The purpose of this paper is to present a method for calculating both the average reservoir pressure and the approximate distribution of pressure within a bounded reservoir that is, a reservoir with no water drive. In reservoirs where the pressure builds up rapidly after wells are shut in, the determination of average pressure generally poses little problem, for one often need only average the final buildup pressures. It is when pressure buildup is slow that difficulties arise. For practical and economical reasons, the time allowable for closing in wells is limited. If at the maximum allowable closed-in time the pressure has not reached a constant value (and this is more often the case than is generally realized), calculation of average pressure presents difficulties.
Pressure information for use in material-balance calculations is obtained, where possible, from pressure build-up surveys in shut-in wells. Using proper extrapolation methods, static pressures are obtained which, by averaging, give the field static pressure.Often, particularly in fields with a large number of wells, only spot pressure readings are available. A graphical method is presented here which enables the determination of the corrections which must be applied to the spot readings to give an estimate of the static pressure. Although the static pressures thus obtained are not so reliable as those from build-up surveys, they are more nearly correct than the spot readings themselves for use in material-balance calculations.
To rank a variety of ventures in the order of their profitability, a yardstick is needed in which both the profit and the time at which this profit is realized are included. This paper describes methods for evaluating two of the more common yardsticks, i.e., the present day value or the total profit for a fixed interest rate and the internal rate of return. No attempt is made to present arguments in favor of either of these criteria. Based on a number of simplifying assumption, tables and graphs have been prepared with the aid of which the profitability of single incomes, constant incomes, and three types of declining incomes can be calculated for a wide range or interest rates. Two examples are given to explain the use of the graphs and tables. Introduction The total profit of a venture is by definition the difference between the total net income and the capital investment. Where, as is usually the case, the investor has a choice of ventures in which he can invest his money, he will need a single yardstick to rank these ventures according to their profitability. It is at once obvious that the total profit cannot always be a sufficient criterion: a smaller profit returned to its investor after a short time may be more desirable than a larger one, for which the investor has to wait a long time. A yardstick by which ventures can be ranked uniquely according to their degree or profitability must therefore incorporate the monetary value of the profits and the time at which they are returned to the investor. Several yardsticks are being used in the oil industry which more or less approach this criterion. In the present paper only two will be considered: the present day value (or deferred value) or the total profit, and the internal rate of return ["yield", "earning power", "rate of return," etc.]
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