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A platform for research: civil engineering, architecture and urbanism
Experience with Hydraulic Fracturing Tests for Stress Measurements in the WIPP
Hydraulic fracturing tests around the WIPP in the Salado salt formation near Carlsbad, New Mexico, demonstrated that the virgin in situ stress state is isotropic and that the stress magnitude corresponds to the weight of the overburden. It was also determined, however, that hydraulic fracturing in rock salt does not render stress measurements directly because all characteristic test pressures are strongly influenced by creep. In this study, the correlation between fracturing pressures and in situ stresses was made by means of finite element analyses and by means of in situ observations of all hydraulically induced fracture patterns. Because of creep, it also appears that the shapes of the pressure-time records in rock salt will be very different from the normal shapes of hydraulic fracturing records in competent hard rock. In particular, (1) stable pressure-time signatures with no distinct change from breakdown to driving pressures are obtained under isotropic far-field loading, (2) instantaneous shut-in pressures are likely to be obscured by fracture pinching, and (3) pressure-time signatures will change with delay time between drilling and hydraulic fracturing for approximately the first 50 days. After that time, a relatively long window appears to open up during which the predicted stress fields around the drillhole are approximately constant. The present results should apply qualitatively to hydraulic fracturing at other sites. However, local differences such as brinehead pressures should be taken into account. (ERA citation 11:030753)
Experience with Hydraulic Fracturing Tests for Stress Measurements in the WIPP
Hydraulic fracturing tests around the WIPP in the Salado salt formation near Carlsbad, New Mexico, demonstrated that the virgin in situ stress state is isotropic and that the stress magnitude corresponds to the weight of the overburden. It was also determined, however, that hydraulic fracturing in rock salt does not render stress measurements directly because all characteristic test pressures are strongly influenced by creep. In this study, the correlation between fracturing pressures and in situ stresses was made by means of finite element analyses and by means of in situ observations of all hydraulically induced fracture patterns. Because of creep, it also appears that the shapes of the pressure-time records in rock salt will be very different from the normal shapes of hydraulic fracturing records in competent hard rock. In particular, (1) stable pressure-time signatures with no distinct change from breakdown to driving pressures are obtained under isotropic far-field loading, (2) instantaneous shut-in pressures are likely to be obscured by fracture pinching, and (3) pressure-time signatures will change with delay time between drilling and hydraulic fracturing for approximately the first 50 days. After that time, a relatively long window appears to open up during which the predicted stress fields around the drillhole are approximately constant. The present results should apply qualitatively to hydraulic fracturing at other sites. However, local differences such as brinehead pressures should be taken into account. (ERA citation 11:030753)
Experience with Hydraulic Fracturing Tests for Stress Measurements in the WIPP
W. R. Wawersik (author) / C. M. Stone (author)
1986
21 pages
Report
No indication
English
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