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Damage Factor in Stress Induced Evolution of Pearmeability Anisotropy: A Possible Future Implication in Petroleum Exploration

R.K. Dubey
Department of Applied Geology, Indian School of Mines University, Dhanbad-826 004, India E-mail : [email protected]

The exploitation of hydrocarbon from the petroleum oil and gas field commonly resulting the flow of petroleum and redistribution of oil and gas pressures causing redistribution of in-situ stress, ultimately resulting in deformation of oil containing and associated seal of cape strata. Moreover such deformation induced change the permeability by evolution of new permeability anisotropy resulted the a site and conduits for further migration of oil and gas from the working sites and strata. Because of development of new mechanical permeability anisotropy the accumulated oil and gases starts escaping from the original oil bearing beds and trap and resulted migration of hydrocarbon towards low stress zone through the newly formed permeability secondary anisotropy causing the possible deviation in design of oil recovery system and pressure draw down like technical and working problems. In addition, in some acquit and severe migration situation the exploration geologist may be bound to start exploration work in associated area on the basis of termination distance of secondary migration of petroleum.

The present paper attempt the problems through creating analogous situation for the same in laboratory to analyze the evolution of stress induced permeability anisotropy with help of concept of damage factor (DE), which one of the aspect of geomechanics and geotechniques. For the purpose the cubical samples of dimension 5x5x5 cm 3 were cored in perpendicular direction to thin bedding and lamination present in sandstone of Upper Kalmar Group, Vindhyan Supergroup collected from Vindhum Fall, Mirzapur, Uttar Pradesh, India due to compositionally homogeneous and geomechanically isotropic in nature. The inherent damage factor (IDF) were measured on cubic samples with help of ultrasonic concrete tester in both parallel to bedding and perpendicular to bedding and anisotropy was calculated as 0.985, which is approximately more closure to 1 (isotropic). The transmission velocity of P-wave in fresh samples is measures along with physical properties and petrological details of samples only in fresh samples. Further, the cubical in fresh and dry condition and samples saturated with water and petroleum were deformed under incremental stress environment on Servo-controlled Material Testing System (MTS) for study of deformation behavior of sandstone and determination of damage factor with help of measurement of transmission velocity of P-wave by using Ultrasonic Concrete Tester. On the basis of stress-strain behavior and concept of damage factor the development of new permeability anisotropy were measured assessed the state of stress induced mechanical permeability anisotropy in case of dry and fresh samples of sandstone and samples saturated with water and petroleum.

The results of investigation reveals that the dry samples in the initial stage of deformation of exhibits decrease in damage factor and approaching towards negative value may be due to closing and collapsing of inherent pore space voids, cracks and fractures, thereafter the damage value is very low and constant for minor increment in stress condition. At higher stress level the change stress –strain behavior shows sharp enhancement in damage with progressive increase in value. The sample saturated with water exhibits higher damage factor in comparison to dry samples before experimentation may be due to filled inherent pore spaces, voids and cracks. The deformation of samples saturated with water under drained condition pertain development of damage factor form initial stage of deformation and the damage factor enhances with high rate even at lower stress levels may be development of pore stress under stressing. However, in case of samples saturated with petroleum pertains development of higher rate in damage factor started from initial stage of deformation and reaches very high value only on low value of stress.

The application of damage factor (DF) concept to analyze the stress induced permeability anisotropy in geological formation resulted from exploitation of petroleum (oil) and change in interface equilibrium between gases, oil and water, oil and gas pressure and flow of petroleum may be applicable as a techno-economic tool for future explorations and prospecting hydrocarbon in area associated with petroleum recovery sites.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery