Abstract
The volume of shale (Vsh) is a critical parameter in petrophysical analysis that enables the accurate estimation of other petrophysical parameters like effective porosity, saturation and Net-to-Gross. This is an important step in characterization of reservoirs as well as valuation of hydrocarbon potentials. GR (Gamma Ray), Neutron and Density as well as Potassium, Uranium and Thorium logs were adopted to estimate and analyze Vsh for sand 4 reservoir interval across five wells using the empirical (GR-linear and non-linear) and Neutron-Density methods. Results show that Vsh estimated by the different methods varied from 0.24 - 0.39 for the GR linear method (highest), 0.12 - 0.24 for the Larionov method (intermediate), and 0.04 - 0.28 for the Neutron-Density method (lowest). Although the Neutron-Density method gives the lowest values of volume of shale, this does not translate to the most accurate and reliable results. This may be attributed to the non-singularity in measurements and varying sensitivities of the well logs used in this method as well as the complexities of the wellbore condition. The GR non-linear (Larionov) method provides consistent and comparable volume of shale estimations with the neutron-density method than the linear GR method and consequently, the non-linear GR method is recommended for estimation of Vsh in the studied field.
Highlights
IntroductionThere exist different methods of estimating volume of shale (Vsh) of a reservoir from well logs, which has been extensively discussed in literature [2] [3] [4] [5]
Well-logs are important downhole measurements in exploration geophysics
The GR non-linear (Larionov) method provides consistent and comparable volume of shale estimations with the neutron-density method than the linear GR method and the non-linear GR method is recommended for estimation of Vsh in the studied field
Summary
There exist different methods of estimating Vsh of a reservoir from well logs, which has been extensively discussed in literature [2] [3] [4] [5] These are the GR, neutron-density, sonic, nuclear magnetic resonance (NMR), neural nets and machine learning methods. The empirical (linear and non-linear) method is the most frequently used Vsh estimators based on the calculation of Gamma-Ray Index (GRI) from GR log [6]. These methods are generally affected by the type and distribution of shale and minimum trace of radioactive materials in the reservoir matrix, which may lead to an overestimation of Vsh in the studied reservoir interval [7] [8]
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