Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

Porosity-based models for estimating the mechanical properties of self-compacting concrete with coarse and fine recycled concrete aggregate

Abstract: Predicting the mechanical properties of Self-Compacting Concrete (SCC) containing Recycled Concrete Aggregate (RCA) generally depends, in great part, on the RCA fraction in use. In this study, predictive equations for estimating SCC mechanical properties are developed through SCC porosity indices, so they are applicable to any RCA fraction and amount that may be used. A total of ten SCC mixes were prepared, nine of which containing different proportions of coarse and/or fine RCA (0%, 50% or 100% for both fractions), and the tenth mixed with 100% coarse and fine RCA, and RCA powder 0–1 mm. The following properties were evaluated: compressive strength, modulus of elasticity, splitting tensile strength, flexural strength, and effective porosity as measured with the capillary-water-absorption test. Negative effects on the above properties were recorded for increasing contents of both RCA fractions. The application of simple regression models yielded porosity-based estimations of the mechanical properties of the SCC with an accuracy margin of ±20%, regardless of the RCA fraction and amount. The results of the multiple regression models with compressive strength as a secondary predictive variable presented even greater robustness with accuracy margins of ±10% and almost no significant effect of accidental porosity variations on prediction accuracy. Furthermore, porosity predictions using the 24-h effective water also yielded accurate estimations of all the above mechanical properties. Finally, comparisons with the results of other studies validated the reliability of the models and their accuracy, especially the minimum expected values at a 95% confidence level, at all times lower than the experimental results.

Assessment of Residual Hydrocarbon Saturation with the Combined Quantitative Interpretation of Resistivity and Nuclear Logs

Abstract: Estimation of residual hydrocarbon saturation remains an outstanding challenge in formation evaluation and core analysis. Standard interpretation methods for nuclear-resistivity logs cannot distinguish between mobile and residual hydrocarbon saturation. In extreme cases, fluid pumpout or production testing are the only options to ascertain whether the reservoir's in-situ hydrocarbon is mobile. We develop a new method to distinguish mobile from residual hydrocarbon and to quantify residual hydrocarbon saturation. The method combines modeling of resistivity and nuclear logs with the physics of mud-filtrate invasion to quantify the effect of residual hydrocarbon saturation on both nuclear and resistivity logs. This strategy explicitly takes into account the different volumes of investigation of resistivity and nuclear measurements and does not assume that the near-borehole region is flushed to the level of residual hydrocarbon saturation. The method begins with an initial multi-layer petrophysical model which is constructed via standard procedures of well-log interpretation and core measurements. Thereafter, we simulate the physics of mud-filtrate invasion and the corresponding resistivity, density, and neutron logs. Initial estimates of residual hydrocarbon saturation and parametric relative permeability are refined until achieving a good agreement between simulated and measured neutron and density logs. Next, we refine initial estimates of water saturation, porosity, and permeability until securing a good match between numerically simulated and measured resistivity logs. The method of interpretation considers two specific options for implementation: (1) quantification of the influence of residual hydrocarbon saturation on the radial distribution of fluid saturation due to invasion, and (2) appraisal of invasion effects on the vertical distribution of fluid saturation within a flow unit that exhibits both hydrocarbon and water saturation in capillary equilibrium. Application examples are described for the cases of tight-gas sand reservoirs invaded with water-base mud (WBM) and oil-bearing reservoirs invaded with oil-base mud (OBM). In the case of tight-gas sands, our method explains the marginal productivity of deeply invaded beds that exhibit cross-over between density and neutron logs. For a 15-porosity unit formation, when the residual gas saturation increases by 10 saturation units, the cross-over between neutron and density logs increases by 2.4 porosity units. Interpretation results indicate measurable sensitivity of nuclear logs to residual hydrocarbon saturation in cases of deep WBM invasion due to immiscibility between invaded and in-situ fluids. However, the accuracy of the method decreases with increasing values of both hydrocarbon pore volume and hydrocarbon density. In the case of OBM invasion, reliable estimations of residual hydrocarbon saturation are possible with relative density differences above 15 percent between mud filtrate and in-situ hydrocarbon.

Hydrophilic and strength-softening characteristics of calcareous shale in deep mines

Abstract: To better understand the mechanism of the strength weakening process of soft rocks in deep mines after interacting with water, a self-developed experimental system, Intelligent Testing System for Water Absorption in Deep Soft Rocks (ITSWADSR), is employed to analyze the hydrophilic behavior of deep calcareous shale sampled from Daqiang coal mine. Experimental results demonstrate that the relation between water absorption and time can be expressed by power functions, and the soakage rate decreases while the soakage increases with time. In order to quantitatively calculate the weight coefficients of the influential factors for water absorbing capacity of rocks, a series of testing methods are adopted, including scanning electron microscope (SEM), X-ray diffraction and mercury injection test. It is demonstrated that the effective porosity has a positive correlation with the water absorbing capacity of rocks and the contents of illite and illite/smectite. The initial water content presents a negative correlation with the water absorption capacity of rocks. According to the absolute value of weight coefficients of various influential factors, the order of magnitude from high to low is captured: initial water content, illite, illite/smectite formation (S = 5%), and the effective porosity. After water absorption tests, uniaxial compressive strength (UCS) tests were performed on rock specimens allowing a linear relationship between the UCS and the water content of rock to be established, indicating that the strength of calcareous shale decreases linearly with the increasing water content.