ИСТИНА

Geophysical Well Logging (GWL) is an important source of information about stress-strain state of the upper Earth's crust. Nowadays there are many methods of mechanical and stress properties estimation around the wellbore are developed and implemented. However, quantitative estimation of maximum horizontal stress (SH) is still quite problematic. This paper is dedicated to reduction of uncertainty on the stage of SH estimation by means of additional information of rock structure from special GWL: full-waveform logging (FWAL) and wellbore imagers (WBI). Straight consequence of this specification is geomechanical model reliability increasing and clearer understanding of naturally fractured reservoirs. This paper was done for oilfield located on the south of Pannonian basin. Productive intervals are associated with crystalline schists of Paleozoic age. These rocks are very dense, have relatively high britlleness and many natural fractures, which are the main drivers for oil production. In this case, geomechanical parameters are closely related with petrophysical properties. The work is based on complex interpretation of conventional and special GWL, which resulted in natural fractures identification and characterization. As one of the possible approaches of qualitative fracture permeability prediction Rock Physics was used. After classification of all fractures on induced and natural, permeable and impermeable it is possible to specify 2 important geomechanical parameters: azimuth of SH and its magnitude. The last parameter is one of the most complicated for quantitative analysis and there is still no direct or general method of estimation. At the same time, by minimization of error around this value, we can achieve several applied benefits: reduction of costs due to optimal well trajectory, mitigation of risks related to wellbore failure, increasing of hydraulic fracturing efficiency etc. Analysis of relationship between stress state of the fracture and its flow properties allowed to estimate the possible range of SH values. Together with calibrated magnitude of minimum horizontal stress (Sh) this approach was used to prepare the complete analysis of main stresses on the examined field.