Study On Calculation Method Of Collision Probability In Dense Wellbores Drilling

With the increasingly complex underground geological conditions faced in oil and gas development,the well pattern is gradually infiltrated,infill wells,cluster wells and multi-branch wells have been widely used.While these technologies have improved the productivity of oilfields,they also resulted in the distance between adjacent wells increasingly smaller,the importance of anti-collision design and optimization of wellbore trajectories pre-drilling,anti-collision monitoring and collision probability calculation in drilling program has also been growing.In the process of drilling or after well completion,it is necessary to use survey tools to measure the related parameters of the current wellbore for the aim of anti-collision monitoring,trajectory control and follow-up evaluation.So far,in the field of dense wells anti-collision design and monitoring in actual drilling program,traditional adjacent wells distance scanning and separation coefficient method are mainly used to evaluate the collision risk of adjacent wells.As these methods are too simplified for complex engineering situations,they can not accurately reflect the collision risk between adjacent wells and can not meet the requirements of dense wells anti-collision monitoring.For magnetic and gyroscopic survey tools,this paper studied the sources and properties of various error terms appearing in survey operation and their influence on borehole position coordinates,proposed a new collision probability calculation method which uses Monte Carlo method to simulate the generation of each error term in wellbore survey operation,calculates the wellbore position under the given values of error terms and make a judgement whether wellbores collide with each other,and gets the collision probability of these adjacent wellbores after a lot of computer tests mentioned above,the correctness of this method is verified by comparing the position distribution range of the survey stations obtained by the above statistical simulation method with the uncertainty range obtained by the ISCWSA error ellipsoid model.Finally,the variation trend of borehole uncertainty range with well depth in different types of survey operations was also studied.This paper also made the significance analysis of the error terms affecting the uncertainty range of wellbores in different types of survey operations,which laid a firm foundation for the future research on how to reduce the uncertainty range of wellbore position and the collision risk between adjacent wellbores.The collision risk of wellbores usually exists in the vertical section and the first build up section.The result of this paper shows that the calculation results obtained by the method proposed in this paper are accurate enough after tens of thousands of Monte Carlo simulations,and the calculation time is short enough for this method to be used under the current drilling engineering conditions,it can provide a reference for the design or analysis of dense wellbore trajectory anti-collision.