Quantitative prediction of multiperiod fracture distributions in the Cambrian-Ordovician buried hill within the Futai Oilfield, Jiyang Depression, East China

Abstract

In the Futai carbonate oilfield of the Jiyang Depression, Bohai Bay Basin, oil enrichment is significantly related to fracture development during the oil production process. In this research, by methods of core observation and image logging interpretation, the tectonic fractures’ characteristics were distinguished. Numerically, through the elastoplastic mechanics method of finite element (FE) simulation, the three-dimensional (3-D) paleotectonic stress field (two key fracture-generating periods) and the current stress field in the Futai buried hill were quantitatively simulated. The equations between fracture parameters and tectonic stresses were deduced to predict the fracture distribution and development in various periods. Simultaneously, through the mechanical superposition algorithm, the fracture parameters under the present conditions were simulated by modifying the current stress field from preexisting fractures. The results indicated that: (1) The Yanshanian maximum principal stress ranged from −85 MPa to −435 MPa in the NWN-SES (344°) (343°–164°) direction. (2) The Himalayan minimum principal stress ranged from 5 to 30 MPa in the NWN–SES direction. (3) The fracture formation during the Yanshanian and Himalayan orogeny was primarily influenced by the regional stress field in the Jiyang Depression or the secondary stress field derived from the Tanlu fault zone, followed by the lithology. The current fracture porosity was primarily controlled by fold, followed by the large faults oriented by N–S direction and then by the secondary faults oriented by E-W direction. With successful calculations, the developed 3-D FE geomechanical modeling and fracture parameter calculation method holds great promise for characterizing fractures in other carbonate reservoirs.