Interference Pressure Transient Test for Permeability Anisotropy Evaluation in Shallow Unconsolidated Reservoir Undergoing EOR Polymer Flood Pilot

Abstract

A shallow, unconsolidated, sour heavy oil reservoir in North Kuwait is under primary production. Due to rapid decline in reservoir pressure, a development scenario was selected consisting of 10 years of water injection secondary recovery followed by enhanced oil recovery (EOR) polymer flood for which a pilot is being implemented. This pilot will provide vital information to establish feasibility for full-field implementation and in this paper, we describe the application of Interference Pressure Transient Test (IPTT) and stress testing. IPTT is utilized for proper understanding of the vertical permeability and permeability anisotropy (Kv/Kh) which are key for evaluating heavy oil sweep efficiency under injection. Stress testing will provide essential information about the cap rock integrity to monitor that water and polymer flooding is contained across the required reservoir. A combination of IPTT and stress testing utilizing the Wireline Formation Testing (WFT) tool and laboratory core analysis were the basis of a selected method for vertical permeability and permeability anisotropy determination. Laboratory measurement for permeability anisotropy has its own challenge due to unconsolidated nature of the formation. IPTT under such conditions can provide reliable and fast measurements, which can also help to calibrate the laboratory measurements later. Four EOR pilot vertical injectors wells were drilled in a symmetric 5-spot pattern, with a central vertical producer. Distance between the injectors is 60 meters, whereas each injector is at 50 meters spacing from the central producer. IPTT was carried out in all four EOR pilot wells, whereas this study involves only three of the injectors. Three-probe configuration along with advanced three-dimensional probe provided comprehensive evaluation for the sand and shaly reservoir intervals. It was observed that main sand body under consideration showed Kv/Kh ranging between 0.05 to 0.15. Some of the main shaly intervals were observed to be either fully isolating the sub-layers or have some vertical communication. It should be noted that downhole fluid analysis and sampling was conducted in one of the wells utilizing WFT. The obtained fluid properties were included in the IPTT analysis for more accurate results. The acquired data from three pilot wells were used to update the reservoir simulation models to have a more representative sweep efficiency evaluation utilizing polymer flooding for the planned EOR. It provides an efficient way to derive the vertical permeability and permeability anisotropy in the challenging unconsolidated formation. This paper adds to the literature of case studies where vertical permeability and permeability anisotropy have been obtained in the challenging environment of unconsolidated formation. It demonstrates how accurate planning combined with advanced technology and innovative workflow yielded the required input data for the dynamic reservoir simulation model.

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