Research Of Calculation Method Of Formation Pressure In Piedmont Belt

Formation pressure is an important engineering geological parameter,which closely links to the exploitation and development of hydrocarbon resources.Accurate estimation and analysis of pore pressure benefits to optimize drilling design,ensure drilling safety and improving drilling proficiency.Through fully survey research in this paper,the state of the field of pore pressure estimation technology is summarized.Also,main reasons impacting pore pressure calculation precision are analyzed.Context and technical route are proposed according to the current difficulties.Currently,there are various formation mechanisms for abnormally high pore pressure.However,not a valid discriminant approach had been proposed to determine the overpressure formation mechanism.Thus,it lacks a solid basis in model selection for pore pressure estimation.In this paper,one method to discriminate the forming mechanisms of abnormally high pressure is presented according to the different logging response of the formation’s loading and unloading procedure and the geological characteristics of typical structure in tectonic compression environments.This method enables us to precisely judge the mechanism of under-compaction,tectonic compression and fluid expansion.This paper summarized the different methods to predict formation pressure regularly.At the meantime,it predicted ten wells’ formation pressure in the North of Qaidam Basin with regular method.It shows that this area exist high pore pressure and the results were predicted with Eaton method are lower than measured generally.For tectonic compression mechanism,Corrected Mean Stress Method is proposed on the basis of three-dimensional compaction theory.This method considers the impaction of the vertical principal stress and two lateral horizontal principal stresses to formation compaction,which overcomes the drawbacks of single-dimensional compaction model and significantly improves the precision of formation pressure calculation.At the meantime,it predicted ten wells’ formation pressure in the North of Qaidam with this method.The inaccuracy of formation pressure calculated with this method is less than ten percent generally,and the results are able to meet the demand of engineering.