Improved water saturation estimation in shaly sandstone through variable cementation factor

Estimation of water saturation, Sw, in shaly sandstone is an intricate process. The surface conduction of clay minerals adds up to the electrolyte conduction in the pore spaces, thus generating high formation conductivity that overshadows the hydrocarbon effect. In each resistivity-based water saturation model, the key parameter is formation factor, F, which is typically derived from Archie’s Law. Referring to a log–log plot between formation factor and porosity, cementation factor reflects the slope of the straight line abiding Archie’s Law. In the case of shaly sandstone, derivation based on Archie’s Law in combination with Waxman–Smits equation leads to higher cementation factor, m*. In the shaly parts of the reservoir, high m* is counterbalanced by clay conductivity. Nonetheless, high m* used in clean parts increases Sw estimation. In this study, the variable cementation factor equation is introduced into the standard correlation of Sw versus Resistivity Index, RI, to develop a water saturation model with shaly sandstone parameters. Data retrieved from two fields that yielded mean arctangent absolute percentage error (MAAPE) were analysed to determine the difference between calculated and measured data within the 0.01–0.15 range for variable cementation factor method. The conventional method yielded maximum MAAPE at 0.46.

An Exact Expression for the Effective Bulk Modulus for Acoustic Wave Propagation in Cylindrical Patchy-Saturation Rocks

Hydrocarbon reservoirs often contain partially gas-saturated rocks that have attracted the attention of exploration geophysicists and geologists for many years. Wave-induced fluid flow (WIFF) is an effective mechanism to quantify seismic wave dispersion and attenuation in partially gas-saturated rocks. In this study, we focus on the local fluid flow induced by variations in fluids in different regions and present a new model that describes seismic wave propagation in partially gas-saturated rocks, namely, the cylindrical patchy-saturation model. Because the seismic wave velocity and attenuation oscillate at high frequencies, it is not ideal for studying dispersion and attenuation caused by WIFF. To avoid the high-frequency oscillation in the cylindrical patchy-saturated model, we use an approximation to the Newman function instead of the full Newman function to calculate the effective bulk modulus. We then calculate the P-wave velocity and attenuation of the proposed model and interpret the lab-measured data. The proposed model is an alternative patchy-saturation model that can explain the problem of high-frequency oscillation and low-frequency attenuation.

The Prostate Saturation Point after Testosterone Replacement Therapy in Testosterone Deficiency Patient

Background: The effect of testosterone on the prostate gland is an unresolved question. The prostate saturation model is a recent hypothesis explaining that the stimulation of prostate tissue by testosterone is limited to a certain level of testosterone due to the limited number of androgen receptors. However, data from the Thai patients related to this issue are still lacking and need to be explored. Objective: To investigate prostate changes after testosterone replacement therapy (TRT). Materials and Methods: A retrospective study including testosterone-deficient patients who had TRT between 2011 and 2017 at Ramathibodi Hospital was conducted. The change in prostate-specific antigen (PSA) levels before and after TRT, or after a 1-year observation, was measured and analyzed as the primary objective. As a secondary objective, the authors measured and evaluated normal PSA velocity (PSAV) in the patients after TRT. Results: One hundred eleven testosterone deficient patients were included for analysis. The mean age was 62 years old. The baseline testosterone level and PSA level at the beginning were 247 ng/dL and 1.16 ng/mL, respectively. After undergoing TRT for one year, the results showed that the testosterone and the PSA levels were 307 ng/dL and 1.46 ng/mL, respectively. In addition, the subgroup analysis illustrated that patients who had low baseline testosterone levels such as 247 ng/dL or less, had significant increase of PSA level after treatment. However, when the baseline testosterone level was more than 247 ng/dL, the PSA levels were steady after treatment. For the secondary-objective results, the PSAV of the testosterone deficiency patients after TRT was 0.3 ng/mL/year. Conclusion: The evidence clearly indicates that TRT significantly increased the serum testosterone level. However, it had a limited effect on PSA change. The present study results supported the hypothesis of the prostate saturation model. The authors believe that a testosterone level of 247 ng/dL can saturate all androgen receptors in the prostate gland and no longer increase prostate stimulation. Keywords: Prostate-specific antigen; Prostate cancer; Testosterone replacement Therapy; Prostate saturation

An improved saturation evaluation method of Chang 8 tight sandstone reservoir in Longdong West area of Ordos Basin, China

This study focus on saturation evaluation of Chang 8 tight sandstone reservoir in Longdong West area of Ordos Basin, China. An improved saturation calculation method was proposed based on the equivalent rock capillary bundle theory. Firstly, according to characteristics of reservoir pore structure and rock conductivity, the conductive space of reservoir rock is equivalent to the parallel conductive of micro capillary bundle representing the micro pores and the coarse capillary bundle representing the macro pores. Then, the variable cementation index(m) saturation model was deduced by using Poiseuille flow equation and Darcy's law. During the calculation of model parameters, the T2 spectrum data of nuclear magnetic resonance (NMR) was used to calculate the equivalent radius of reservoir micro pores and macro pores, which ensured the ability of model popularization and application. Finally, the proposed saturation calculation method is applied to reservoir evaluation of the study area, and compared with the classical Archie saturation model. The application effect shows that the calculated saturation from the proposed variable m model is much closer to the sealed coring data than that from classical Archie model, and the average relative error of saturation calculated by the variable m model is within 7%, which proves that the proposed saturation calculation method is applicable and effective.

Transient rhyolite melt extraction to produce a shallow granitic pluton

Rhyolitic melt that fuels explosive eruptions often originates in the upper crust via extraction from crystal-rich sources, implying an evolutionary link between volcanism and residual plutonism. However, the time scales over which these systems evolve are mainly understood through erupted deposits, limiting confirmation of this connection. Exhumed plutons that preserve a record of high-silica melt segregation provide a critical subvolcanic perspective on rhyolite generation, permitting comparison between time scales of long-term assembly and transient melt extraction events. Here, U-Pb zircon petrochronology and 40Ar/39Ar thermochronology constrain silicic melt segregation and residual cumulate formation in a ~7 to 6 Ma, shallow (3 to 7 km depth) Andean pluton. Thermo-petrological simulations linked to a zircon saturation model map spatiotemporal melt flux distributions. Our findings suggest that ~50 km3 of rhyolitic melt was extracted in ~130 ka, transient pluton assembly that indicates the thermal viability of advanced magma differentiation in the upper crust.

A model for multicomponent diffusive bubble growth in magmas

<p>Bubble growth is one of the key processes that govern the degassing of magmatic systems and drive volcanic eruptions. Typically, the gas exsolution process begins with the nucleation of bubbles in an oversaturated melt and continues with bubble growth. Bubbles grow by mass diffusion, when the silicate melt is oversaturated in volatiles, and by mechanical expansion as a response to pressure decrease. The viscosity of the surrounding melt and the surface tension oppose a resistance to bubble growth and control the mechanical disequilibrium between the bubbles and the melt itself. The combination of the Rayleigh-Plesset equation with a diffusion equation represents a common approach to describe diffusive bubble growth. A number of models have been developed for describing bubble growth dynamics in magmas, most of them accounting for a single volatile specie. Nevertheless, the multicomponent nature of magmatic volatiles has long been recognised to play a major role in controlling magmatic exsolution process. Here we present a model describing bubble growth in magmas in the presence of multiple volatile species through a fully non-ideal multicomponent saturation model.  Numerical simulations show the role of the different species (e.g., water and carbon dioxide) in the dynamics of diffusive bubble growth for different melt compositions. The new model is implemented in the MagmaFOAM library,  a dedicated computational tool to solve multiphase flows characterizing magmatic systems that extends the open-source library OpenFOAM. Within the MagmaFOAM framework it is possible to combine the bubble growth model with fluid solvers in order to fully capture the multi-scale nature of liquid and gas phases in magmatic systems.</p>