Since its introduction in the petroleum industry, hydraulic fracturing has been one of the primary engineering tools for reservoir stimulation and well productivity enhancement. Creating a conductive channel in a reservoir to increase hydrocarbon recovery is a complex operation involving a variety of aspects including geology, petrophysics, production engineering, geomechanics, and fluid mechanics. Designing a treatment to achieve the desired fracture dimensions and orientation is intimately connected with rock mechanics.
A mechanical earth model was built in support of a hydraulic fracturing treatment performed on the Achimov formation in the West Salym oil field, Western Siberia, operated by Salym Petroleum Development. This deep and laminated formation is suspected to lie above water-bearing layers, which makes its stimulation technically challenging.
The study involved various petrotechnical skills. First, the modeling of the rock mechanical properties required standard wellbore measurements and acoustic logging. The calibration of the minimum horizontal stress profile was achieved by post-closure analysis of the minifracture performed before the main fracturing treatment, and by interpretation of temperature logs. Then, the fracture growth was simulated using hydraulic fracturing software. Analysis of the main treatment was augmented with bottomhole pressure (BHP) recorded by a memory gauge installed in the wellbore. The simulated BHP could thus be compared with and matched to the measured BHP in order to calibrate the fracture model. Finally, fracture mapping by the differential cased hole sonic anisotropy technique allowed for verification of the obtained geometry and the suspected orientation. This unique combination of measurements and analyses enabled a thorough evaluation of fracture parameters that can be extended to neighboring wells.
Geomechanics modeling has proven to be an invaluable tool in the struggle to understand and predict fracture growth, as well as to optimize fracturing treatments. The accuracy of the preliminary fracture design helped to define the best solution very early. By employing the described approach, remarkable knowledge was gained on the local state of stress, which will have a positive impact on reservoir management and field development planning.
