Transient Pressure Behaviour in Fractured Reservoirs

Abstract

This paper was presented as part of the student paper contest associated with the European Petroleum Conference. Abstract This paper gives an overview over the different aspects of transient pressure behaviour in fractured reservoirs. Basically fractured reservoirs can be divided into two different groups. The first consists of reservoirs of single porosity which have been fractured artificially, the second group consists of reservoirs which contain a network of natural fractures and which have been additionally fractured artificially(double porosity fractured reservoir). Further it is possible to make a difference based on the radial dimensions and the boundary conditions of a reservoir. Therefore the systems of infinite and finite reservoirs will also be discussed. These four cases will be presented separately. The different flow regimes will be discussed and also the parameters which influence the pressure behaviour. Further the interpretation of the pressure tests will be discussed by using the type curves which correspond with the results of the flow regimes description. Finally a short brief of the simulation of the two main different fractured reservoirs on a numerical reservoir simulator will be given. Introduction To enhance the productivity of wells which were damaged or were completed in tight formations, hydraulic fracturing (called "HF" in the following text) is a common and often used technique. Hydraulic fracturing as well as acidicing have been used with great success in many reservoirs with low natural permeability. It was realised very early that a HF influences the flow behaviour of a well extremely, so that common pressure test analyses techniques may cause errors. Thus the transient flow behaviour of fractured reservoirs became an important topic. The different analyses of the pressure tests do not only describe the status quo of the flow behaviour after the treatment but describe also the form of the HF. The interpretation of the tests is very important for the production strategy and even for the design of a new HF.