A Technique for Measuring Permeability Anisotropy and Recovering PVT Samples in a Heavy Oil Reservoir in North West Siberia

Abstract

Wireline formation testers provide the measurements for the determination of formation pressure gradient, in-situ effective oil mobility profile, in-situ downhole fluids analysis (DFA) as well as taken PVT samples and maintaining them in single phase condition for lab analysis, interval pressure transient testing (IPTT) for characterizing of permeability anisotropy and in-situ minimum horizontal stress estimations. Pressure and fluid samples are obtained by setting a rubber packer and small diameter probe. The packer hydraulically isolates a small part of the formation from the hydrostatic pressure, while the probe enables communication between the tool and formation. This conventional technique is well suited for thick and permeable formations. However, for difficult conditions such as laminated formations or formations with low matrix permeability and formations saturated with high viscosity fluids or fractured limestones, application of a single probe technique is limited. Under these conditions, the small packer may not be able to isolate the zone, may miss a thin zone or in a formation with very low permeability and/or high fluid viscosity the contact area with the packer may be too small to let the fluid flow. To help overcome this, technique of Wireline Formation Tester (WFT) with dual packer module is used. This wireline conveyed straddle packer has the capability of hydraulically isolating a minimum of one meter of formation. The dual packer can be set repeatedly at different locations on a single trip in the well. Using these modules, pressures, real-time formation fluid identification, PVT samples, permeability and flow rate estimations can all be evaluated in detail. Within the vast Russian oil and gas fields environment with different geology, and wellbore and fluids conditions, the technique of combining probe and dual packer modules in one string and running the tool on TLC (tough logging conditions) has been applied successfully to a thinly reservoirs, formations with low permeability and unconsolidated formations saturated by high viscosity fluids (heavy oils). In this paper, application of interval pressure transient testing done during formation fluid cleaning up from mud filtrate and during downhole fluid identification is described. The main objective of using the formation tester was to take downhole representative PVT samples of high viscosity fluid in a high invasion wellbore environment in three exploration wells of a new remote field. Use of dual packer for PVT sampling and single probe and vertical observation probe together provided possibility to estimate permeability anisotropy, in spite of difficult and challenging acquisition (operations were done from Geophisika Logging unit due to the field remoteness) and wellbore conditions (well bore stability and high mud filtrate invasion). Introduction There are large reserves and resources of heavy oil present on the Eastern European (Russian) and Siberian platforms, where at least 700 billion bbl is present. Heavy oil and natural bitumen reserves and resources of the Siberian platform comprise one of the three largest accumulations in the world, the other two being the Western Canada basin and the Eastern Venezuela basin 1. Understanding the nature of reservoir fluids is essential for the optimization of completion, facilities design and reservoir production strategies. Gas oil ratios, saturation pressures and viscosities are among the fluid parameters that determine the economic viability of a field development. Downhole fluid analysis (DFA) is a powerful technique to help identify compositional grading and frequently missed compartmentalization of the developed reservoirs. Formation fluid sampling earlier in the life of a well ensures that necessary information is available for reservoir completion planning and decision-making. This is in particular important in heavy oil environment, where a flow assurance is a major concern.