Understanding Wellbore Storage Effects to Interpret Buildup Pressure Data from Hydraulic Fractured Vertical Wells in Low-Permeability Reservoirs

摘要

Pressure transient tests have been widely used to characterize hydrocarbon reservoirs,not only because they can provide reliable estimations of reservoir pressure but they also help understand reservoir geometry and well productivity.For this study,real-time buildup tests were performed to analyze the success of fracturing procedures carried out in vertical wells to improve their productivity,previously affected by the commonly low-permeability nature of the reservoir target. Understanding when infinite-acting radial flow(IARF)occurs during a buildup test is crucial because it directly affects the estimation of reservoir and well parameters such as reservoir pressure,effective permeability,and the skin factor;the primary output typically obtained from pressure test analysis. However,when strong wellbore storage effects occur,the pressure data can be misinterpreted and incorrect property estimation results may be produced,leading to a false perception of the treatment effectiveness. The main objective of the study is to show how to develop a realistic interpretation of actual real-time pressure data when there are phase segregation phenomena taking place in the wellbore,which can be wrongly associated to a reservoir response.Performing dynamic and static pressure gradient tests in the wellbore,before and after the buildup test,is very useful in validating the results.