The Synergy of Geological and Technological Aspects is the Key to Successful Fracturing of the Source Rocks
Authors: Ostapchuk Marina , Kuznetsov Vadim , Antonenko Aleksandr , Konchenko Andrey , Vereschagin Sergei , Terleeva Ekaterina , Demin Vladimir 
Published: October 2016

This paper describes the results of an integrated approach to selecting the optimal interval of horizontal well drilling followed by hydraulic fracturing as part of a pilot project of developing unconventional hydrocarbon reserves in the oil-source rock of Bazhenov suite in the southern licensed territory of the Priobskoye field. The battery of research included a lithological identification based on composition and presence of movable hydrocarbons in voids, permeability and porosity assessment, as well as assessment of mechanical properties and stress profile with intent to develop a reservoir fracturing model that would guarantee the best coverage of potentially producing interval of the section.

Bazhenov suite rocks have a fairly complex and vertically unsteady mineralogical composition, and their voids are characterized by a complex structure. Research results helped build a lithological model that allows capturing the intervals of occurrence of rocks with void structure, which demonstrates presence of movable oil. The presence of movable oil was also confirmed by the integrated petrophysical model that allowed a quantitative assessment of porosity and permeability of identified potentially producing intervals.

Identification of anisotropic dynamic moduli of elasticity using the cross-dipole full-wave acoustic logging (FWAL) in the open hole, as well as identification of elastic and structural behavior based on core samples helped develop single-well models of mechanical properties. Their further adjustment to core data using hydraulic fracture control results and reiterated FWAL helped formulate several scenarios of the fracturing process.

The key method of identifying structural and compositional complexes in the well section is clustering based on two well logging techniques, i.e. pulsed neutron gamma logging and nuclear magnetic logging. While developing the integrated petrophysical model of Bazhenov suite oil-source rocks, we saw demand for a practical classification that could offer the most comprehensive description of clusters identified by logging. This classification of rocks was developed on the basis of rock composition data obtained during lithological and geochemical tests of core samples. Voids description was based on the results of petrographic analysis and NML data, which helped identify voids with potential fluid flow for two structural and compositional complexes of Bazhenov suite rocks.

Bazhenov suite interval in the southern licensed territory (SLT) of the Priobskoye field is characterized by high fracturing gradients, which means a hydraulic fracture cannot be contained in absence of vertical stratification and anisotropy.

A lithological and petrophysical model augmented by the mechanical properties simulation results was employed to assess vertical fracture growth, which helped formulate the best design of hydraulic fracturing to contain the fracture within the potentially producing interval and ensure the longest half-length of the fracture and the largest stimulated reservoir volume.

A comprehensive approach to assessing section properties that identify both presence of movable hydrocarbons and potential for successful hydraulic fracturing helped find the interval of hydraulic fracture initiation that best supports high production rates. The study demonstrates that containment of fracture in a potentially producing interval is one of the key drivers and a controlling factor of successful hydraulic fracturing operation.