In Situ Stress Measurements in Inclined Holes in the North Sea: Application to Enhanced Oil Recovery

摘要

Eighteen in situ stress measurements were made in two 3.5 km deep wells in a reservoir located in the Viking Graben region of the North Sea. The wellbores were inclined 60 exp 0 and 70 exp 0 from the vertical. The principal in situ stress directions and magnitudes were determined by the anelastic strain recovery method. The principal stress directions were determined directly from measurements of the principal strain recovery directions of oriented core immediately after it was retrieved from the wellbore. The principal stress magnitudes were calculated from the principal strain recovery magnitudes, overburden stress, and elastic properties of the rock using a creep recovery model. The reliability and accuracy of the strain recovery method has been documented in several vertical holes by direct comparison with open hole hydraulic fracture stress measurements. In the two inclined holes in the North Sea, the maximum principal stress was the overburden, and the average ratios of the maximum and minimum horizontal stresses to the overburden were 0.93 and 0.78, respectively. The azimuth of the maximum horizontal stress (and hydraulic fracture) was N72 exp 0 W +- 21 exp 0 . The measured stress orientations are consistent with a geologic and tectonic model of the region. The calculated stress magnitudes indicate that potential hydraulic fractures created during the EOR program will be vertical and have a well defined azimuth because the overburden is the maximum stress and there is sufficient difference between the two principal horizontal stresses. The high ratio of the minimum stress to overburden indicates that high injection pressures will be required during stimulation, and this should be included in the stimulation design to optimize fracture length. Fracture length will depend upon the permeability of the formation, water quality, the total injected volume, and injection pressures. (ERA citation 10:038749)