One of the dimensionless reservoir parameter which can be used to characterize reservoir is the diffusivity coefficient. Diffusivity coefficient is a ratio of medium's capacity for transmissibility of fluid to its capacity for strong or releasing fluid; diffusivity provides a quantitative measure for the rate of response during transient fluid flow. It is a parameter that is derived from the analysis of well test data. The objective of this work was to determine diffusivity coefficient for the Asmari sedimentary layer in an Iranian Southern oil fields. To achieve this objective, initially all available information such as petrophysical data, PVT data, production data and pressure build up data of the completed wells in Asmari formation were collected. Twenty one build up tests data were analyzed by using Pan System Software using appropriate model for each well to estimate the parameters such as permeability, skin factor, well bore storage, average reservoir pressure and so on. A correlation between productivity index and the diffusivity coefficient for the Asmari formation has been obtained. The proposed correlation is very useful for determination of reservoir permeability for the situations where enough well tests data are not available.
The first step for reservoir studies is the reservoir identification from the reservoir engineering view. One of the greatest problems facing the petroleum engineering is that of characterizing physical nature of the subterranean reservoir from which the crude oil is produced. The significance, which can be put on the results of sophisticated numerical simulations of reservoir performance, is entirely dependent on the quality of reservoir description inherent in the model (11, 12, and 13). There are several ways by which it is possible to gain information about the reservoir characteristics, there are:
Seismic and associated geological studies.
Information obtained during the well drilling; this comprises:
the analysis of cutting and coring and
the interpretation of various logs.
pressure testing of wells and
Analysis of reservoir performance, e,g. through history matching.
Note that in the reservoir development stage only item 1, 2 and 3 are applicable and important engineering decisions will be made on the basis of rather spars and sometimes conflicting evidence (1, 2, 3,6,7,8 and 9). As one needs different medical experiments to get aware of his health, to study the reservoir better and tack its performance into account, the reservoir must be tested by different well tests. In the order word as a medical experiment determine the person's illness, the well testing also determine the condition of well, with respect to its performance.
The pressure behavior of an oil or gas well is both a normally measurable and a very useful entity. In the context of pressure testing it is the pressure at the bottom of the well adjacent to the producing formation, referred to as the bottom hole pressure (BHP), which is of significance. The pressure analysis of wells essentially concerns the dynamic relation between the producing rate, the BHP and the average reservoir pressure in the vicinity of the well under consideration.