| Abstract | Fractured granite basement reservoirs were discovered in 1987 in Cuu Long basin, Vietnam. Although there have been a number studies on this special type of reservoir, in general, researches are still limited at best and not yet systematically done throughout.
Here, in this study the micro flow behavior of fractured granite reservoirs will be investigated using wireline logging and well test data analysis.
First of all, a summary of fractured granite basement reservoirs in Vietnam was made. Previous researches on fracture behavior on well log and well test curves and methods to analyze these data were reviewed. In this research, fractured porosity was calculated by using the Pirson’s method as well as using density curve. From well log interpretation, one can detect the fractures and calculate the combine fracture porosity (both macro and micro fractures). By integration with well test analysis using the Bourdet derivative method, it was possible to distinguish between flow from micro fracture and macro fracture.
Well logging data from 5 wells of block A were collected and interpreted by using Techlog software. The results included lithological zoning, total porosity and fracture porosity. Lithological zoning are divided by using log curves, composite logs, PLT interpretation and mud loss which includes weathered zone, tight zone and fractured zone. With weathered granite zone, the range of total porosity is from 0.05 to 0.11, fracture porosity is between 0.006 and 0.016. In fractured zone, the range of total porosity is from 0.01 to 0.17, the fracture porosity is between 0.004 and 0.07.
Similarly, well test data from 5 wells of block A were collected and analyzed by using Ecrin software. The outputs contain permeability, skin, wellbore storage, inter-porosity flow coefficient, storage ratio values. The permeability (k) runs from 1.42 mD to 3,170 mD, wellbore storage (C) is from 0.0009 to 0.0655 bbl/psi, skin is from -0.3 to -7.66, storage capacity (ω) is from 0.0032 to 0.15, inter-porosity (λ) is from 1.32E-10 to 3.49E-7 .The inter-porosity flow coefficient and storage ratio values indicate the ability of flow, fracture density and storage of fracture respectively. These values may present the appearance of micro flow. |