Analysis of Wireline Interval Pressure Transient Test Data From Multi-Layered Reservoir Systems
Authors: Tang Chuin Cherng , Onur Mustafa 
Published: March 2015

Abstract
This study examines the methodology of the packer-probe wireline formation tests (WFT) to interpret and analyse the pressure transient data acquired at the packer and probes along the wellbore for single layer and multi-layered systems. Such tests are often called WFT interval pressure transient tests or simply WFT IPTTs. IPTTs offer some advantages over the conventional (extended) well tests in terms of cost, time, and providing important properties such as horizontal and vertical permeability over a scale larger than cores but smaller than that of extended well tests. In this project, the same methodology applied to a packer-probe WFT in single layer system will be applied to various multi-layered systems to investigate the feasibility and validity of using the single-layer analysis methodology for the WFT IPTTs conducted in multi-layered systems because only a few of researchers have considered interpretation of packer-probe interval pressure-transient tests in multi-layered systems. Thus, one of the main objectives in this study is in detail to access the methodology used for analyzing a single layer system and apply the same to multi-layered systems. Various averaging formulas of horizontal and vertical permeabilities will be used to represent a multi-layered system. The validity of the representation is tested through pressure response matching. The results show that an "equivalent" single-layer analysis based arithmetic averages of the horizontal and vertical permeability can be used to analyze the IPTTs acquired in multi-layered systems provided that the heterogeneity is not large (i.e., Dykstra-Parsons coefficient is less than 0.4 for spherical flow analysis and is less than 0.06 for radial-flow analysis).

Introduction
Wireline formation testing is a part of pressure transient testing methods. It is an evolution of DST, Drill Stem Test. DST usage is limited to the hole condition and the cost of repetitive runs of DST for formation evaluation. Thus, wireline formation tester is often used for formation evaluation work. This method is usually performed in an open-hole using a cable-operated formation tester with sampling module ability which is anchored down-hole while the communication is established by several pressure and sampling probes. The first tool was introduced in the 1950's concentrated on fluid sampling. RFT (Repeat Formation Tester) is then introduced to add capability of the tool to repeatedly measure formation pressure in a single run into the well (Ireland et al. 1992). Since 1962, common applications of wireline formation tester are:to obtain formation pressure and reservoir pressure gradient,to determine reservoir fluid contacts,to obtain fluid samples for formation fluid characterization,to estimate reservoir permeability and skin, andto characterize reservoir.
According to (Schlumberger, 2006), pressure transient tests are conducted at all stages in the life of a reservoir; exploration, development, production and injection. During exploration stage, tests are conducted to obtain fluid samples and static pressures of all permeable layers of interest. These pressures can be used to obtain formation fluid gradient to identify fluid contact in the reservoir. During development stage, the emphasis is on static reservoir pressures, which are used to confirm fluid contacts and fluid density gradients. On that basis, the different hydraulic compartments of the reservoir will be determined and tied into geological model. During production stage, tests are for reservoir monitoring and productivity tests to access to need for stimulation.