Abstract
Hydraulic fracturing has become a common completion treatment or stimulation treatment for horizontal wells; however, effectiveness of these treatments, in terms of improved production, is difficult to predict. One reason for uncertain production results is poor fracture initiation in the reservoir, which can be caused by drilling-induced damage or a formation's natural resistance to breakage.
Several approaches have been attempted to solve this problem and provide a better return on completion investment. One approach that has achieved strong initial results is the use of dipole sonic logs to determine closure stress. From closure stress, formation breakdown pressures can be determined, which are used to design more effective treatments and place them more efficiently in the well and reservoir, where breakdown pressures are lower. This paper presents research to validate this approach.
Two wells were selected in the same area and geologic setting. The first was completed using standard processes for this asset. A dipole sonic log was run in the horizontal wellbore before beginning the completion. Results from the sonic log were compared to the fracture treatments after the fact.
In a second vertical pilot well, information was acquired, including elemental capture, dipole sonic, and nuclear magnetic resonance, with the objective of determining rock texture, vertical and horizontal rock mechanical properties, effective porosity, and permeability. A dipole sonic was then run through the horizontal section of this second well to determine anisotropy. This knowledge was used to select perforation and stage points in the horizontal well and design fracture treatments.
Two additional reservoirs are included in this paper where dipole sonic logs were run only in the horizontal cased hole but reference nearby pilot holes. Results from all cases were positive; therefore, it is believed that this technique can be useful in any reservoir.
