The purpose of well stimulation is to increase the contact area of the wellbore in the reservoir to maximise production rates. This is achieved through fractures penetrating the reservoir. These fractures tend to show either infinite conductivity with double lines half slope or finite conductivity with quarter slope on the log-log plot of pressure change versus elapsed time depending on the permeability and other parameters of the formation. These flow behaviors are clear indications of a stimulated well. However, observations in some post frac tests where a single slope line is reported indicate non-fractured well response.
The objective of this paper is to investigate the unusual flow behavior associated with fractured well tests following a proppant frac job. To author’s knowledge, this behavior has been referred to briefly in a limited number of publications with no clear explanation. The aim of this study is to address this problem in detail and suggest that this behavior is due to a variety of reasons assuming the frac job has targeted the reservoir interval of interest. The controlling factors are fracture lengths, fracture conductivity, the damage caused by the fracture operation including choke fracture effect and less importantly, fracture face skin and non-Darcy effect in the case of gas wells.
The study utilizes 3-D numerical simulation black oil and compositional models comprising of single and multi- layered reservoirs. Study results show that the investigated problem is likely to be associated with damaged fractures of short lengths and low fracture conductivity values. Knowledge obtained from the study is applied to the analysis of well tests from actual fractured wells. The importance of this paper is that understanding the behavior of fractured wells is important to operator and service companies.