Due to the cost of extended pressure-drawdown or buildup well tests and the possibility of acquisition of additional information from well tests. the modern trend has been toward development of well-test anal ysi s methods pertinent for short-time data. "Short-time" data may be defined as pressure information obtained prior to the usual straight-line portion of a well test. For some time there has been a general belief that the factors affecting short-time data are too campI ex for meaningful interpretations. Among these factors are well bore storage. various skin effects such as perforations. partial penetration. fractures of various types. the effect of a finite formation thickness. and non-Darcy flow. A number of recent publications have dealt with short-time well-test analysis. The purpose of this pappr is to present a fundamental study of the importance of wellbore storage with a skin effect to short-time transi ent flow. Re suI ts indi cate that p roper interpretations of short-time well-test data can be made under favorable circumstances.Upon starting a test. well pressures appear controlled by well bore storage enti"e/y, and data cannot be interpreted to yield formation flow capacity or skin effect. Data can be interpreted to yield the wellbore storage constant. however. After an initial period. a transition from wellbore storage control to the usual straight line takes place. Data obtained during this period can be interpreted to obtain formation flow capacity and skin effect in certain cases. One important result is that the steady-state skin effect concept is invalid at very short times. Another important result is that the time required to reach the usual straight line is normally not affected significantly by a finite skin effect.

This pa~r was selected for presentabcm by an SPE Prcgram Committee following rev!aw of Imformat!on W"tai"ed M a" abstract $&mifted by tha authm(s) Co"te"ts of the pap,gr, aa presentad, have not baen reviewed by the Swety of Patroleum Engmaers and ara subject to mrrecbon by the author(s) The material, as presented, does not necessarily reflect any poslbon of the Society of Petroleum Engineers, Its offIcars, or membrs Papers presented at SPE meetmgs are sublect to publl=bon rev!aw by Edltorlal Committees of the Smtety of Petroleum Engineers Electromc reproduction, d!stribubon, or storage of any part of this papar for wmmem!al pu~ses w!thl the wrttten wnsant of the Society of Petrolaum Engineers IS prohrbltad Perm!sslon to raprcdum Im print is rastrlcled to an abstract of not more than 300 words. !llustrabons may not be cop!ed The abstract must contain Wnsplcuous nowledgment of where and by whom the pa~r was presented Wr!te L!brarlan, SPE, P O Box 8338w, Rtiardson.~75083-38%, U. S A, fax 01-972.952-9435Abstract This paper presents new production decline curves for analyzing well production data from radial and vertically fractured oil and gas wells, These curves have been developed by combining Decline curve and Type curve analysis concepts to result in a practical tool which we feel can more easily estimate the gas (or oil ) in place as well as to estimate reservoir permeability, skin effect, fracture length and conductivity, etc. Accuracy of this new method has been verified with numerical simulations and the methods have been used to perform analyses using production data from several different kinds of gas wells. Field and simulated examples are included to demonstrate the applicability and versatility of this technology.Decline curve analysis methods, in a variety of forms, have been used in the petroleum industry for more than fifiy years to analyze production data and forecast reserves. Type curve analysis methods have become popular, during the last thirty years, to analyze pressure transient test (e.g. buildup, draw-down) data.result is the development of these new production decline type curves.These new production decline type curves represent an advancement over previous work because a clearer distinction can be made between transient and boundary dominated flow periods.The new curves also contain derivative finctions, similar to those used in the pressure transient literature to aid in the matching process. These production decline curves are, to our knowledge, the first to be published in this format specifically for hydraulically fractured wells of both infinite and finite conductivity. Finally, these new curves have been extended to utilize cumulative production data in addition to commonly used rate decline data.

In recent years, there has been a great interest in the "slug test"11), which involves the instantaneous removal of a specific quantity of fluid from a wellbore and measurement of the resulting pressure-time response. Although a skin effect term was introduced by Jaeger, most recent studies have not considered a skin effect in analyzing slug test data. A new approach to conventional well-test analysis by Earlougher and Kersch was used to prepare type curves for the slug tech which include the skin effect.This study includes: results presented in both tabular and graphical form to aid application, a new material on the radius investigated and the time of duration of slug test, and the presentation of field example illustrating the application and important limitations of the method, as well as limitations of conventional DST analyses. The main application of the slug test method is in the analysis of pressure data for cases wherein the fluid influx into the drill pipe tends to kill the flow (sometimes even before the tester valve is closed). On the other hand, many field test have been observed wherein the phenomena of critical (acoustic velocity) flow destroys the application of the method. The slug test, as currently developed, does not consider critical flow. Introduction THE (@HART from the upper (not blanked-off,) pressure gauge n a conventional DST is often illustrated is ihowrl in Figure 1-a. The pressure trace increases as the tester is lowered into the mud Column and the mud-column pressure is measured prior to opening the tool (see point A). Opening the tester valve causes a sharp drop in pressure to point B, the start of the first flow period. From point B to C, the pressure increases linearly, indicating a constant-rate flow as the li(juid level rises in the drill string. Point C repre-sents the start of the first shut-in, and line C-D is the first shut-in pressure buildup. Point D represents the first closed-in pressure (CIP). The tester vaIN,e is then opened and the second flow is shown by line _ E-F, again representing a constant-rate flow period bv vit-tue of the linear increase in pressure with time. This Indicates that the liquid level is increasing at .1 f-onSt@Lnt rate, and the storage volume within the drill pipe is a constant per foot of length of drill pipe. Often a sharp bend is evident in line E-F when the (irill -@ollar is filled and the liquid begins to rise in fhe di-ill pipe, which has a larger inner diameter than the di-ill collar. Finally, line F-G represents the secon(i Shut-in, and iS L@sually analyzed by means of a Horner presstire-buildlip graph.Th(!re are, of course, many legitimate deviations from the DST chart shown in Figure I-a (see Black"), Figure 1-b shows an anomaly that is com-mon in the testing of water wells, but which also oc-curs in certain oil-well tests. Point A' indicates mud-('ollimti pressure, a--, in Figure I-a, but the flow I)erioct, B'C', is quite different from B-C ( Fig. I-a). 'Fhe pre;slire trtce is not linear with time. A deel@Ining ;lope is shown, indica...

Currently, type curve analysis methods are being commonly used in conjunction with the conventional methods to obtain better interpretation of well test data. Although the majority of published type curves are based on pressure drawdown solutions, they are often applied indiscriminately to analyze both pressure drawdown and buildup data. Moreover, the limitations of drawdown type curves, to analyze pressure buildup data collected after short producing times, are not well understood by the practicing engineers. This may often result in an erroneous interpretation of such buildup tests. While analyzing buildup data by the conventional semi-log method, the Horner method takes into account the effect of producing time. On the other hand, for type curve analysis of the same set of buildup data, it is customary to ignore producing time effects and utilize the existing drawdown type curves. This causes discrepancies in results obtained by the Horner method and type curve methods. Although a few buildup type curves which account for the effect of producing times have appeared in the petroleum literature, they are either limited in scope or somewhat difficult to use.In view of the preceding, a novel but simple method has been developed which eliminates the dependence on producing time effects and allows the user to utilize the existing drawdown type curves for analyzing pressure buildup data. This method may also be used to analyze two-rate, multiple-rate and other kinds of tests by type curve methods as well as the conventional methods. The method appears to work for both unfractured and fractured wells. Wellbore effects such as storage and/or damage may be taken into account except in certain cases.The purpose of this paper is to present the new method and demonstrate its utility and application by means of example problems.References and illustrations at end of paper.

This pa~r was selected for presentabcm by an SPE Prcgram Committee following rev!aw of Imformat!on W"tai"ed M a" abstract $&mifted by tha authm(s) Co"te"ts of the pap,gr, aa presentad, have not baen reviewed by the Swety of Patroleum Engmaers and ara subject to mrrecbon by the author(s) The material, as presented, does not necessarily reflect any poslbon of the Society of Petroleum Engineers, Its offIcars, or membrs Papers presented at SPE meetmgs are sublect to publl=bon rev!aw by Edltorlal Committees of the Smtety of Petroleum Engineers Electromc reproduction, d!stribubon, or storage of any part of this papar for wmmem!al pu~ses w!thl the wrttten wnsant of the Society of Petrolaum Engineers IS prohrbltad Perm!sslon to raprcdum Im print is rastrlcled to an abstract of not more than 300 words. !llustrabons may not be cop!ed The abstract must contain Wnsplcuous nowledgment of where and by whom the pa~r was presented Wr!te L!brarlan,