The Fracture Characterization and Assessment of Gas Potential with Advanced Formation Tester in Low Permeability Fractured Carbonate Reservoir

Abstract

Abstract Carbonate reservoirs can exhibit heterogeneity in terms of porosity, permeability, fractures, vugs and wettability. This heterogeneity affects well performance, completion and reservoir management development decisions. Although extensive logs are run for the petrophysical evaluations in these formations, the use of advanced wireline formation testers (WFTs) can greatly aid in reservoir description. WFT not only can identify hydrocarbon bearing formations but also plays a vital role in fracture characterization and calibration of fracture models. Advanced petrophysical logs were used to identify potential pay intervals, while high resolution image logs to delineate fractured zones and static fracture parameters, such as dip, azimuth and aperture. It has been shown that fracture dynamic properties, such as conductivity, can be quantified via pressure transient analysis using wireline formation tester in addition to fluid analysis. In this paper, WFT data was used to understand the pressure behavior of naturally fractured reservoir containing a network of discrete finite-conductivity fractures. The study presents results obtained from advanced logging suite that was run to characterize complex low porosity and low permeability carbonate reservoir where natural fractures provide primary pathways of fluid flow. Advanced wireline formation tester with straddle packer and fluid analyzer were used to test potential intervals. Two out of several intervals were enabled to flow, identifying mobile gas. The pressure transient response confirmed the complexity of reservoir and dominant contribution to flow regimes from fractures in these two intervals. Dynamic fracture properties were characterized through pressure transient analysis and were integrated into fracture model. On the other hand, flow could not be established in number of other intervals indicating tight matrix and no flow contribution from fractures, leading to calibration of geological models. The novelty of approach is the use of wireline formation tester not only to measure formation pressure and acquire downhole samples but to characterize dynamic fracture properties to calibrate fracture model.