Effective porosity

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

Study of threshold gradient for compacted clays based on effective aperture

Abstract: Compacted clay liner plays a crucial role in preventing leakage and migration of pollutants. Clay often appears in Non-Darcy phenomenon, one of which is characterized by having the threshold gradient. The threshold gradients exhibited by different clays are usually quite different. The reason for the discrepancy is currently unknown. To solve this problem, the mineral compositions of two clays were selected for test. The tests included threshold gradient, aperture and the pore water content. The test results showed that kaolin-based Clay A had no threshold gradient, whereas illite and Montmorillonite-based Clay B presented the threshold gradient that decreased with the increase of the porosity. For the samples mixed with Clay A and Clay B, the values of the threshold gradient increased with increasing the content of Clay B in the mixed samples. The reason is that the porosity and mineral content can affect the bound water content. If the value of pF is greater than 3.8, the bound water is gelatinous “immobile water”. Based on the water retention curves, the effective porosity can be obtained by subtracting the volume occupied by “immobile water” from the void of the soil particles. Then the modified effective aperture can be obtained by Hangen-Poiseuille law. The modified effective aperture will decrease with the decrease in the porosity and the increase of the content of illite and montmorillonite. This is the key reason why the different clays have different values of the threshold gradients.

Evolution and Models of Shale Porosity During Burial Process

Abstract: Through the analyses of shale porosity data from core test and logging interpretation,this paper demonstrates the shale porosity evolution trend and points out the difference of porosity evolution between normal compaction and under-compaction.Three reasons which caused difference in porosity evolution are discussed:(1)For the high quality shale during oil generation peak,the over-pressure which was generated during hydrocarbon generation slows down porosity decline rate,which is the main factor explaining why shale remains relatively high porosity at middle-deep depth.Over 5%of porosity increment was contributed by over-pressure.(2)For the high quality shale during middle-late gas generation period,nano-pores originated in hydrocarbon generation processes is another important factor causing the increment of porosity in organic-rich shale,which contributes 1.8%in average to the porosity evolution in shale.(3)The organic acid dissolution affects less to shale porosity increment.Based on the conclusions above,we have built three-stage normal compaction model,under-compaction model and nano-pore originating in organic matter correction model,analyzed the key parameters of the model and proposed a template for estimation of the face pore ratio in organic matter.

Methods for estimating petrophysical parameters from well logs in tight oil reservoirs: a case study

Abstract: Estimating petrophysical parameters from well logs plays a significant role in the exploration and development of tight oil resources, but faces challenges. What's more, the methods for petrophysical parameters from well logs are paid little attention at present. In this paper, the typical tight oil reservoirs of Northwest China are used as an example. Based on the characteristics of mineralogy and fluids in the study field, the rock is assumed into five components which are clays, quartz and feldspar, carbonates, kerogen and pore fluids (porosity). The sum of kerogen content and porosity is defined as the apparent porosity. Then, two porosity log response equations are established. Once the clay content is determined by an individual method, the quartz and feldspar content, carbonate content and apparent porosity are calculated through the established equations. The kerogen content is the difference of the apparent porosity and porosity from nuclear magnetic resonance (NMR) logs. This paper also presents a new approach that combines the complex refractive index method (CRIM) and pseudo Archie method to compute saturation from dielectric logs, which avoids selection for the dielectric constants of each of the minerals. The effectiveness and reliability of these methods are verified by the successful application in the study of the target tight oil play in Northwest China.

A simple model for describing variation of permeability with porosity for unconsolidated sands

Abstract: There is some experimental evidence that the relationship between permeability and porosity is not always linear sime-logarithmic. Different theoretical models that relate the permeability, porosity and particle size are reviewed and discussed. The Kozeny-Carman relationship is extended to model the flow of fluid between soil particles and flow of fluid around soil particles. It is demonstrated why for low porosities the relation between permeability and porosity is linear semi-logarithmic but at high porosities it becomes non-linear. Experimental data for heavy oil bearing sands has been characterized using this non-linear (quadratic) model.