This paper investigates the effects that rock and fluid properties impose on the production history of a well or lease as revealed by a decline curve. In particular, the effects on the constants of the exponential, hyperbolic, and harmonic decline curve equations are reported. An improved method is presented for analyzing production histories, with two field examples illustrating the method. Introduction The extrapolation of production decline curves to predict future oil production has a long history. The word "decline" is a misnomer; "decline curve" is a descriptive term for a graphical presentation of some aspect of the performance history of a well or lease. The graph may show a decline, an incline, or may remain flat. Through the years, the most commonly used decline curve, and the curve usually maintained by oil companies. is the production rate vs time curve plotted on semilog graph paper.The analysis of a decline curve provides two important items of information:the remaining oil and gas reserves to be expected, andthe remaining productive life of a well or lease. In addition, an explanation of any anomalies that appear on the graph is also useful. In recent years, it has been increasingly important to determine the combination of these items so that an accurate yearly estimate of future production can be made. This information is obtained by an analysis of the past performance as shown on the production rate vs time curve. The curve then is extrapolated into the future, and estimated future yearly production is taken from the extrapolated portion of the curve. Decline Curve Analysis Problems Three basic problems associated with the extrapolation process are connected with the historical development of decline curve analysis and have been considered basic assumptions since being defined by Arps. These assumptions are as follow.1. The extrapolation procedure is strictly empirical, and a mathematical expression of the curve based on physical considerations can be set up only for a few simple cases.2. Whatever causes governed the trend of a curve in the past will continue to govern its trend in the future in a uniform manner.3. The decline exponent b in the equations developed by Arps (Table 1) must have a value of 0.0 less than b less than 1.0.Because of empirical extrapolation, a decline curve usually will have a wide range of interpretations. The range of interpretations depends on the production stage of the property. If there is limited prior production history (i.e., a new well), there is a wider range of interpretations possible than for a well or property in the stripper stage of production. Also, each specific interpretation is a function of the experience, integrity, and objective of the evaluating engineer.Various controllable and uncontrollable influences or causes govern the production performance of a well or lease. Some of these influences are as follow. Controllable1. Prorated production.2. Remedial work on producing wells.3. Fluid or gas injection into the producing reservoir.4. Production problems, shutdowns, etc.5. Problems with scale, paraffin, etc.6. Limitations of producing equipment.7. Changes in operating personnel. JPT P. 1327^

De an of t he Gra duate Co lle ge 696363 ii ACKNOWLEDGMENTSThe writer wishes to express his appreciation to his wife and all members of his family for their kindness and consideration during this investigation. The courtesies and cooperation which have been extended by the entire faculty, staff, and students

The extrapolation of oil well production decline data 'intothe future has long been accomplished through the use of semi-log and log-log plots of the data. These conmonly used methods encompass a family of hyperbolic decline curves. The object of such extrapolations is to determine the future production capacity of the oil producing unit.

Publication Rights Reserved This paper was presented at the University of Oklahoma-SPE Production Research Symposium in Norman, Okla., April 29–30, 1963, and is considered the property of the Society of Petroleum Engineers. Permission to published is hereby restricted to an abstract of not more than 300 words, with no Illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Technology or the Executive Secretary. Such abstract should contain conspicuous acknowledgement of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request providing proper credit is given that publication and the original presentation of the paper. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract The measurement of pore space volumes in small cores is commonly accomplished by immersing the cores in a liquid, so that all air other than that contained within the pore space in the core can be readily expelled from the apparatus. Then, after sealing the apparatus, the pore volume can be measured by expanding the air which had been contained in the pores. Mercury is commonly used for this purpose. However, there are some objections to the use of mercury, one being that after such measurements are completed some mercury usually is left within the core so that it is not suitable for further experimental determinations of rock properties. This paper presents the experimental results obtained when using lubricating oil rather than mercury for immersing the cores in making the pore volume measurements. The common calibrated plunger type of apparatus was used. Tn testing one group of cores, the viscous nature of the Oil was the only different limiting the entry of oil into the pores. In testing a second group of cores, the cores were chilled and the pores were sealed by dipping the cores into wax-bearing oil so that wax congealed on their surface before they were immersed in oil in the porosimeter. Finally, the pore volumes of all cores used were measured by immersing the cores in mercury in the customary manner. Excellent agreement was obtained between the pore volumes measured by the two methods, particularly for the second group of cores, where the pores were sealed with wax when oil was used, as compared to the pore volumes measured when the same cores were later immersed in mercury. Introduction The work described in this paper was concerned primarily with the measurement of the volume of the interconnected pores within small core samples, as they exist under surface conditions in the laboratory. Tn general, when determining porosity, which is expressed as a fraction or percentage of the bulk volume, it is desirable to obtain a measure of the pore volume within the rock specimen. By definition the pore volume is the difference between the bulk volume and the volume of the solid mineral framework, and by mathematical relations the determination of any two of these quantities permits the calculation of the porosity. However, where the pore volume is essentially calculated as the difference between the bulk volume and mineral volume, relatively small percentage errors in either or both of these can result in larger errors in the calculated value of porosity. This condition becomes more severe as the pore fraction becomes smaller and consequently the values of bulk volume and mineral volume approach each other.