Study On Near-wellbore And Wellbore Integrated Simulation On Production Performance In High Sulfur Gas Reservoirs

The high-sulfur gas reservoir fluid contains non-hydrocarbon gases such as H2S and CO2,and there is elemental sulfur dissolved in.The presence of water and acid gases effects the fluid properties of hydrocarbon reservoirs.Along with the recovery of gas reservoir,the fall of pressure reduces elemental sulfur solubility,if the gas reservoir temperature is higher than the freezing point of elemental sulfur under this pressure and temperature,sulfur will precipitate in liquid form which makes the gas flow become the complicated gas-water-liquid sulfur phase fluid.Liquid sulfur deposit in the near-well-bore pore and pore and throat of the formation will lead to the decline of reservoir porosity and permeability.The elemental sulfur contained in the wellbore fluid will affect the calculating of temperature and pressure distributions in well-bore.Fluid seepage in the reservoir and flow in the wellbore is a continuous process and interacts with each other.In order to more accurately predict the production dynamics of high-sulfur gas reservoirs,this paper divides the high-sulfur gas reservoir production system into two subsystems which contains reservoir seepage and flows in the well bore.Mathematical model of reservoir gas-water-liquid sulfur seepage and wellbore flow model is established respectively,and taking the bottom hole flow pressure,sulfur solubility and gas well production as the boundary conditions,dynamic simulation of integrated production of wellbore and near-wellbore reservoir of high-sulfur gas reservoir.With the goal of integrated research on near-well reservoir and wellbore,the main achievements of this paper are as follows:(1)Aimed at the exist of acidic gas and water and make deviation factor,density,viscosity corrections.Analyze the way in which elemental sulfur dissolves and precipitates and the sulfur deposition impact on reservoir properties and wellbore flow.Coming to conclusions that acid gas physical properties change with pressure,the water in the gas mainly affects the viscosity of the gas.Sulfur deposits are mainly carried out in physical form.When the gas reservoir temperature is higher than the freezing point of elemental sulfur under this pressure and temperature,sulfur will precipitate in liquid form will make influences on reservoir physical properties,well bore pressure and temperature distribution.(2)Established a matrix-fracture mathematical model which could describe the gas-water-liquid sulfur seepage in the near-wellbore zones of high-sulfur gas reservoirs,solve the equation.By comparison with actual production wells data to verify the model correctness.The results show that water production,gas production,and initial sulfur content have a greatly impact on bottom hole pressure.(3)Aimed at fluid flow characteristics of wells in high-sulfur gas wells,a model was built which can calculate wellbore pressure and temperature for single gas phase,gas-water-liquid sulfer phase,gas-water-solid sulfer phase,and do pressure-temperature coupling calculation.By comparing the calculation results with the commercial software Pipesim in the condition of the gas reservoir has no sulfur,the result shows the correctness of the model.Analysis shows sulfur is precipitated in the gas,gas production,initial H2S content has a greatly impact on wellbore pressure but has little influences on wellbore temperature.(4)Analysis of the necessity of integration calculation of formation wellbore,using flowing bottomhole pressure and reservior production as a boundary condition,continuous solution with continuous solution the gas reservoir and wellbore to realize integrated production dynamic analysis.(5)Integrated simulation through practical examples,the results show the reservoir calculation of the bottom hole flow pressure equal to the wellbore calculation of the bottom hole flow pressure which proves that the integrated simulation of this paper is correct,the presence of water and sulfur has an impact on the simulation.Study on the presence of sulfur,the results show that sulfur is precipitated in liquid form,and complex gas-liquid sulfur seepage occurs in the near well reservoir and wellbore.Simulation of integrated reservoir and wellbore shows gas production,water production,initial sulfur content has a greatly impact on gas well production time,bottom hole flow pressure and wellbore pressure distribution,but has a little impact on temperature distribution.A small amount of H2S existence has little impact on gas reservoir production.