Abstract
The laboratory experiments on samples from Kirthar fold belt of lower Indus basin Sindh Pakistan were carried out to investigate the effect of gas slippage under varying conditions of pore pressures and overburden stress. The samples were dried in an oven at temperature of 600C and were randomly selected for measurement of permeability and porosity. Permeability was measured using nitrogen gas, while the porosity measurements were made using helium gas expansion porosimeter. The bulk volume was determined by measuring sample diameter and length with caliper. The permeability results suggest that gas slippage increases as if low pore pressures are used, which leads to higher measured permeability than intrinsic permeability of samples. An attempt was also made to estimate the permeability using existing correlations and found that there is large scatter in predicted permeability and measured data. This large amount of scatter in the predicted permeability values concludes that unless absolutely necessary, such correlations should not be used where accurate absolute permeability values are needed. Moreover, the permeability and porosity were plotted together to develop a relation between two properties; the power law fitting of the data well explains the relation between permeability and effective porosity.
Highlights
Tight rock formations are important in many ways either to produce the gas, oil, to meet the energy needs or to store the CO2 and nuclear wastes into underground earth, as these rocks exhibits extremely low permeability [1,2]
It is essential to characterise the flow of gas within such tight rock formation having very small pore throats and the changes, which might occur within their permeability due to pore pressures and overburden stresses changes that need to be examined
EXPERIMENTAL RESULTS AND DISCUSSIONS The slippage corrected gas permeability of Kirthar fold belt tight sands were conducted under range of overburden stress and varying pore pressures
Summary
Tight rock formations are important in many ways either to produce the gas, oil, to meet the energy needs or to store the CO2 and nuclear wastes into underground earth, as these rocks exhibits extremely low permeability [1,2]. The permeability measurements conducted at low pore pressures need to be corrected to take into account of gas slippage effects to obtain accurate permeability values.in a low permeability porous medium, the pores with their diameter equal to mean free path of the gas molecules further enhances the gas flow within pore walls i.e. the slippage flow of gas molecules resulting in increased rate of flow of the gas as well as the apparent permeability [5]. In petroleum industry single permeability measurement is conducted at a low gas pore pressures, and corrected for Klinkenberg effect to get the gas slippage factor values. To check the validity of such assumption a comprehensive study has been conducted and results are reported
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