Discrepancy between measured dynamic poroelastic parameters and predicted values from Wyllie’s equation for water-saturated Istebna sandstone

Abstract

The drilling-related geomechanics requires a better understanding of the encountered formation properties such as poroelastic parameters. This paper shows set of laboratory results of the dynamic Young’s modulus, Poisson’s ratio, and Biot’s coefficient for dry and water-saturated Istebna sandstone samples under a series of confining pressure conditions at two different temperatures. The predicted results from Wyllie’s equation were compared to the measured ones in order to show the effect of saturation on the rock weakening. A negative correlation has been identified between Poisson’s ratio, Biot’s coefficient and confining pressure, while a positive correlation between confining pressure and Young’s modulus. The predicted dynamic poroelastic rock properties using the P-wave value from Wyllie’s equation are different from measured ones. It shows the important influence of water saturation on rock strength, which is confirmed by unconfined compressive strength measurement. Linear equations have been fitted for the laboratory data and are useful for the analysis of coupled stress and pore pressure effects in geomechanical problems. Such results are useful for many drilling applications especially in evaluation of such cases as wellbore instability and many other drilling problems.

Empirical Correlations between the Hydraulic Properties Obtained from the Geoelectrical Methods and Water Well Data of Arak Aquifer

“…Regarding the hydraulic conductivity, Figure 13 demonstrates the close relationship between both hydraulic conductivity calculated from the water wells and VES technique. The corresponding empirical correlation can be written as: = 0.02 ( ) + 0.08 + 5.24 (17) where and are the hydraulic conductivity gained from the water wells and VES technique, respectively. Similar to the porosity, as the hydraulic conductivity of the rock increases, the value of the hydraulic conductivity estimated by the VES technique becomes closer to the water wells' results.…”

“…k Well = 0.02 (k VES ) 2 + 0.08 k VES + 5.24 (17) where k Well and k VES are the hydraulic conductivity gained from the water wells and VES technique, respectively. Similar to the porosity, as the hydraulic conductivity of the rock increases, the value of the hydraulic conductivity estimated by the VES technique becomes closer to the water wells' results.…”

“…In situ stresses surrounding the porous rocks are referred to as the most effective factors in the fluid movement underground [14][15][16]. According to the poroelasticity theory, water extraction through the water wells affects the in situ stress by reduction in pore volume, and fractures' closure [17,18]. Reversely, change of in situ stress influences on the pore deformations and may cause land subsidence, seismic activities and even water well blockage [19].…”

Empirical Formula for Dynamic Biot Coefficient of Sandstone Samples from South-West of Poland

“…Refs. [20][21][22][23][24] expressed that temperature can dramatically change the fluid motion and sample deformations. The reason is that the temperature changes the rheological properties of the fluid such as viscosity.…”

Understanding Slovakian Gas Well Performance and Capability through ArcGIS System Mapping

“…The wells must be situated in suitable rock-bearing environments, e.g., in sandstones Because of its structure, sandstone allows the accumulation of hydrocarbons such as oi and natural gas. For drilling applications in the evaluation of cases such as borehole in stability and many other drilling problems, it is necessary to analyze the effects of bound tension and pore pressure in the bearing rocks [3,4].…”