Some Practical Considerations in the Analysis of Pressure Data

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Abstract
A number of recent studies have brought about an increased understanding of pressure behavior using log-log graphs. This paper presents field examples pressure behavior using log-log graphs. This paper presents field examples not previously discussed in the literature and compares the applicability of type curves with conventional semilog techniques. Introduction Every year a substantial amount of new material on pressure analysis of wells appears in the literature. pressure analysis of wells appears in the literature. This "information explosion" is mainly restricted to the development of new solutions requiring a considerable amount of sophisticated mathematical ability. Except for a few publications, the use of these solutions for analyzing well-test data is not well documented. Thus, the engineer is faced with the problem of efficiently organizing new material. The first objective of this paper is to document use of some of the new information that has appeared in the literature by considering its application to field examples. The advantages of using the newer log-log type curve in conjunction with older semilog techniques will be presented. presented. The second objective is to present new solutions regarding the effects of wellbore storage and skin on pressure behavior of vertically fractured wells. Very little pressure behavior of vertically fractured wells. Very little information is available in the literature regarding the effects of these two parameters on pressure behavior. In some instances, data can be analyzed erroneously if these two factors are not taken into account. Field examples of wellbore storage and skin effects in fractured wells are presented. presented. An interesting feature of modem well-test analysis is the ability to handle short-time data. The term "short-time" refers to data taken before the traditional straight-line portion of the pressure trace commonly used in the analysis of oil and gas well performance. It includes effects of wellbore storage, damage, perforations, partial penetration, and well stimulation such as fracturing or penetration, and well stimulation such as fracturing or acidizing. During the past 25 years a number of methods aimed at interpreting data before the start of the conventional straight line have been presented; however, wide usage of short-time data on a routine basis has come into vogue only recently. The main tool in the interpretation of these data is the log-log type-curve matching procedure. Log-log type-curve procedures, however, are not procedure. Log-log type-curve procedures, however, are not limited to analysis of short-time data. As shown in Refs6, 7. and 8, long-time analyses such as the detection of faults, interference between wells, decline curves, etc., also may be handled using the log-log graphical techniques, provided the appropriate master type curve is available. Analysis of Pressure Data in Fractured Wells In oilfield practice, one encounters many kinds of fracture systems. They include (1) wells intersecting natural fractures, (2) hydraulically fractured wells with fractures of infinite conductivity (propped fractures), (3) hydraulically fractured wells with finite flow-conductivity fractures, and (4) wells producing from naturally fractured or jointed systems but not directly intersecting the high-permeability, secondary porosity system. In addition, fractures may be vertical, horizontal, or inclined. This discussion is restricted to Cases 1 and 2. Only vertical fractures are considered. As mentioned in the Introduction, analyses of pressure transient data in vertically fractured systems are subject to distortion by wellbore storage and skin effects. JPT P. 1256

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