The Analysis of Critically Stressed Fractures with Reconstruction of Tectonic Stresses for Ranging the Area by Production Rates via Example of Riphean Carbonate Fractured Reservoir

Abstract

In this study, the geomechanical analysis of the Riphean fractured carbonate resevior of East Siberia is provided. The research of fissuring and its further deformation mechanism is necessary both for drilling risk assessment (prediction of fluid losses zones due to intensive natural fracturing) and for ranging of perspective drilling zone in terms of its productivity. For described reservoir it is supposed, that natural fractures are the main driver of wells productivity. Reservoir rock is characterized by low average matrix porosity (lower than 3%), which does not influence wells productivity. As for fractures system, according to production logging (spectral noise survey), wide-bend acoustic logging (Stoneley wave interpretation), formation imager (resistivity and acoustic), drilling data (fluid losses) it was concluded that not all fractures are permeable. Comparison of fracture characteristics from different surveys shows that working intervals according to SNL mismatch with permeable intervals from Stoneley wave interpretation and do not fit with maximum fracture density intervals from formation imager. The analysis showed mismatching of productive intervals from Stoneley wave interpretation and SNL results and absence of direct correlation between fracturing and productive intervals for both methods. This can be explained by low amount of working fractures: less than the half of horizontal section works. Moreover, the risk of drilling throught "dry" zone, where no permeable fractures exist, was confirmed by several unsuccessfull wells. On the base of geological and morphological fracture features such as intensity, dip angle, orientation there is no ability to subdivide dry and permeable fractures. That is why for better reservoir understanding the mechanism of fracture occurance, development and activation is analysed. Application of geomechanical modeling for fractures assessment and subsequent forecast of productive zones is rather nontrivial and complex task that required abandoning the traditional approach of creating a geomechanical model in which the main emphasis is on a wellbore stability calculation.