The treatments in petroleum engineering are greatly affected by the value and heterogeneity of tectonic stress, which has direct influence on the distribution of horizontal principal stress. For example, the borehole wall sloughing in drilling and the unbroken reservoir in fracturing will hinder the construction program and add the construction cost. Therefore, basing on the mechanics analysis of linear elastic rock, the formula is established among the maximum and minimum horizontal stress with the tectonic stress coefficient, considering that horizontal principal stress is made up of the overburden gravitational stress component and the tectonic stress component. Then, the tectonic stress coefficient in the direction of the maximum and minimum principal stress can be calculated on the base of the rock mechanical experiment parameters and fracturing work data. According to the tectonic stress coefficient calculated by this method, the horizontal stress is computed in two wells which are located in the same tectonic zone of Santanghu Basin in Tuha oil field. It is indicated that the field data and the computational result fit well and the error is small. Hence, the tectonic stress coefficient could be used in stress analysis and fracturing design for other wells in the same regime. Also, the analysis method may be applied in other oil and gas field.
In-situ stress is the interior stress of crustal rocks and plays an important role in exploration and development of oil and gas fields (Cipolla C L 1994), which forms the basicwork data for field development plan, fracturing design, reservoir fracture prediction, wellbore stability analysis, oil and gas rich region forecasting and so on. Due to the influence of geological tectonism, horizontal principal stress contains the tectonic stress component except for the overburden gravitational stress component(Wills D G & Biot MA 1977,Walls J D 1991).