Effect of Vibration on Rock and Fluid Properties : On Seeking the Vibroseismic Technology Mechanisms

Abstract

ABSTRACT This paper is a laboratory study to investigate changes in rock and fluid properties in accordance with the most important vibroseismic parameters, i.e., frequency and amplitude.Experiment are conducted to obtain porosity, permeability, capillary pressure, end point of relative permeability, residual oil saturation which represent rock properties and oil viscosity whcih represent fluid properties.The results of thelaboratory study on synthetic cores indicate that vibration stimulation can improve the porosity (f) up to 15.3 % and the absolute permeability (kabs) up to 2.2 %, decrease the residual oil saturation (Sor) upto 53.6 %, decrease theirreducible water saturation (Swirr) up to 25 % (decrease the capillary pressure), increase the end point of oil relative permeability (kro) up to 73 %, and increase the end point of water relative permeability (krw) up to 76 %. This study also shows that there is an optimum frequency and amplitude that yield the most significant effect. The results show that frequency of 10 Hz and the maximum amplitude yield the maximum changes in these rock properties. Experiments on sandstone-field sample cores yield that the original porosity of 4.84 % - 26.73 % and absolute permeability of 231.46 mD - 1113.59 mD can be increased in percentage as a high as 53.9 % with an average of 36.6 % from the original porosity, and as high as 54.1 % with an average of 59.4 % from the original permeability. Moreover, the original residual oil saturation varying from 0.15 % - 0.57 % can be decreased up to 68 % with an average of 66.1 %. On carbonate cores, the results are not as encouraging as for sandstones'. The resulted optimum frequencies are 15 Hz and 10 Hz for reducing the residual oil saturation, and porosity/permeability, respectively. The differences between the residual oil saturation before and after the vibration vary from 14.18% up to 54.14% at this optimum frequency. The porosity changes vary from -18% up to 42 % (cek), and permeability changes vary from -28% up to 29 % (cek angkanya).This means that the vibration could not improve or even damage the rock properties if we do not apply the correct optimum frequency. In oil viscosity investigation, for the samples that has viscosity of 0,66 cp and 1.1 cp at 1000 psig, the viscosity measurement is conducted at temperature of 70oC, 85oC and 95oC for 1000 psig, 1500 psig, 2000 psig, 2500 psig and 3000 psig.For the lower viscosity sample at temperature of 70oC, the viscosity reduction at optimum frequencyand maximum amplitude is proven to be increasing with the increasing pressure, it varies from 19,38% up to 22,6%. However, for temperature 85 oC, the viscosity reduction is about 30%, and for temperature of 95oC is about 15%. The highest viscoty sample yield viscosity reduction at temperature of 85oC ranging from 27 - 28%. The laboratory study results on the field core prove the success of the vibration stimulation technology with caution in selecting the optimum frequency, and hopefully, it may give contribution knowledge on the mechanisms of the vibroseismic technology.