Well logging interpretation methodology for carbonate formation fracture system properties determination

Marek Stadtműller

doi:10.1007/s11600-019-00351-w

Abstract

The article presents the methodology for the qualitative determination of fracture zones in the profiles of carbonate formations, based on the complex fracture analysis (CFA) method. Three additive fracture ranges were distinguished, characterized by successively increasing aperture and fracture length values, operatively named micro, meso and macro. Furthermore, the quantitative characterization of fractures with different apertures was done. The methodology of laboratory data integration, fracture porosity and fracture permeability measurements performed on thin section and polished section was described as part of the quantitative well logging data interpretation procedure which uses the FPI (fracture porosity index) parameter. The research was performed in the Lower Carboniferous limestone formation that builds the Paleozoic basement of the Carpathian orogeny. An original software dedicated to the analysis of the wellbore images, obtained with the XRMI Halliburton scanner, was used to identify the presence of macro-fractures, determine their aperture and estimate fractures porosity and permeability in the profile of the analyzed rock formation. As a result of the work, postulates regarding the methodology for collecting research material were formulated, in particular: the scope of different laboratory core samples measurements and well log types. The principles of the optimal methodology for identifying fractured zones and quantitative evaluation of petrophysical parameters of recognized fracture systems were defined.

Highlights

Carbonate formations are generally characterized by a very complex porosity system containing primary porosity and secondary porosity system which consists of discontinuities with various apertures from micro-scale, below 0.1 mm through meso, above 0.1 mm to macro, which can be visible without microscope
Zones with increased concentration of fissures correspond with the anomalies recorded on individual well logging curves, especially URAN, SPHI and DPHI, and in these intervals we observe a significant increase in borehole diameter
Summing up the performed research and obtained results, the following postulates regarding the optimization of the procedure for the interpretation of well logs data using laboratory measurements to identify and parameterize the fractured formation with double porosity can be formulated:

Summary

Introduction

Carbonate formations are generally characterized by a very complex porosity system containing primary porosity (matrix porosity) and secondary porosity system which consists of discontinuities with various apertures from micro-scale, below 0.1 mm through meso, above 0.1 mm to macro, which can be visible without microscope. The secondary porosity includes all forms of caverns, vugs and voids in rock of various origins. Such rocks are called “double porosity rocks” (Archie 1952; Lucia 1999). The general approach to qualitative fracture analysis is the methodology of complex fractures analysis (CFA) proposed by (Sowiżdżal and Stadtműller 2010). This approach assumes the use of well log data as a specific indicator of the presence of fractures that are interpreted simultaneously and allow to divide the analyzed formation into: fracture zones, partially fractured zones and zones without the presence of discontinuities. The secondary porosity prediction must be based on laboratory tests conducted on the representative

Methods

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Discussion

Conclusion