Analysis Of Influencing Factors Of The High Sulfur Content Of The Geological Environment Of Reasonable Pressure Difference Of Over-balanced Drilling

Sour gas reservoir occupies approximately twenty-five percent of the whole gas resources in our country. Owing to hydrogen sulfide may often overflow from bottom hole, it is difficult to the whole drilling in geological environment with high hydrogen sulfide. it is one of key questions that bottom pressure is efficiently controlled and security drilling is performed to decide the hole bottom differential pressure during overbalance drilling . The method of overbalance drilling is generally applied to gas well with hydrogen sulfide and the differential pressure is decided according to character of mud , performance need of pulling out of the well, the gas move rules in mud, and etc. Effect factor of the hole bottom is studied and it is important.This article concretely elaborates the harm of H₂S, analyzes the cause of formation and feature of geography environment of it, brings forward the anticipate ways in the specific condition, studies the effect which H₂S enforce on the pseudoreduced pressure, the pseudoreduced temperature, density and viscosity. The article erects the model about gas-liquid's two-phase flow while H₂S invades theannulus by applying the rheology, the fluid mechanics and the invaded gas's high-temperature and high pressure physical property. The two phase model is setup and programs are compiled in Matlab6.5 for it.The model is applied to calculate the pressure of bottom hole with including the hydrogen sulfide and no including and the result with the hydrogen sulfide is higher. The effect on bottom hole pressure including the mud density , the mud viscosity , wellhead back pressure , delivery volume , the rate of gas cut bottom hole are calculated and the result shows that mud density and wellhead back pressure for the effect on bottom hole pressure is largest, rate of gas cut is larger than mud viscosity and delivery volume . It is obvious for operating condition of drilling working to affect the hole bottom pressure and flowing pressure in well. This article has mainly studies effect of the cycle with stopping drilling , the speed of trips , fluctuation pressure, and etc.According to civil industry standard, the safe additional pressure of mud is applied to balance the decreasing pressure because of swabbing pressure and static pressure during pulling out of the well. In order to prevent overflow ,a additional pressure should be added to balance them. Through study ,the rules of hole bottom pressure and dynamical pressure affected by gas invasion with hydrogen sulfide should be recognized and applied ,and the result is reasonable ,during deciding the density of the mud.