Abstract: The Xing'anling group's tuffaceous sedimentary rock and the Budate group's epimetamorphic rock in Hailaer oilfield belong to low porosity and extra-low permeability reservoir, being characterized by poor physical property, low natural productivity and sensitive hydraulic fracturing effectiveness. A thorough understanding of the current ground stress of the reservoirs can help to determine such parameters as occurrence, length and width of fractures in fracturing design, reducing blindness of hydraulic fracturing operation. Analysis of the existed stress calculation model considering both tectonic stress and thermal stress is made in combination with real well logging data from this oilfield, and the ground stress interpretations of Bei-28, Bei-16 and Su-131 blocks are given, obtaining the stress profiles and the lithomechanics parameters along depth, and mathematical models for stress calculations in different blocks. The calculated vertical and plane stress distribution rules indicate that Xing'anling group's sedimentary reservoir is in lower ground stress and preferable linear distribution feature in different depths, while Budate group's epimetamorphic reservoir appears in big difference of stress, with unclean the linear distribution rule. Applying wave velocity's anisotropy, viscous remanence method, the wellbore caving method and thermal strain recovery method, it is determined that the maximal plane major stress direction ranges from 99° to 107° and the minimal plane major stress direction is from 9°and 17°.

Key words: Hailaer oilfield, ground stress, well logs, lithomechanics parameter