Research On Productivity Prediction And Water Invasion Law Of Horizontal Wells In High Sulfur Fracture Bottom Water Gas Reservoirs

High-sulfur fracture bottom water gas reservoirs are widely distributed throughout the world,such as the Canadian Waterton gas field,the Sichuan Yuanba gas field,and the Sichuan Puguang gas field.In the process of exploiting this kind of gas reservoirs,the formation pressure decreases,the fractures tends to close,the porosity and permeability is reduced due to sulfur deposition,and the bottom water will invade the gas reservoir through the fracture.The existing gas reservoir seepage theory does not fully consider the influence of these factors,which leads to inaccurate productivity prediction and unclear water invasion law of high-sulfur fracture bottom water gas reservoirs.It is of great practical significance to carry out the research on productivity prediction and water invasion law of horizontal wells in high sulfur fracture bottom water gas reservoirs for productivity evaluation and development plan design of such reservoirs.Based on the analysis of geological characteristics and development characteristics of high-sulfur fracture bottom water gas reservoirs,the sulfur deposition prediction of horizontal wells in fractured gas reservoirs is carried out,the productivity prediction formula of horizontal wells in high sulfur bottom water gas reservoirs is derived,and the influencing factors of productivity are analyzed.Using fluid mechanics and seepage mechanics,a three-dimensional gas-water two-phase seepage model for high-sulfur fracture bottom water gas reservoirs,considering bottom water invasion,fracture sulfur deposition and stress sensitivity,is established.A numerical simulation program is compiled by MATLAB software,and the reliability of the model is verified.On this basis,the effects of sulfur deposition,production,water parameters and the ratio of fracture to matrix permeability on productivity and water invasion are analyzed.The main achievements of this paper are as follows:1.Sulfur deposition mainly occurs within 2m of the wellbore.The longer the production time and closer to the wellbore,the higher the sulfur saturation;the smaller the initial porosity,the more serious the sulfur deposition damage;the smaller the fracture opening and the shorter the length of the fracture,the easier the sulfur deposition to block the flow passage;the higher of the production,the faster the sulfur deposition,so reasonable production can effectively prevent the occurrence of sulfur plugging.2.During stable production period.horizontal well productivity is mainly affected by gas reservoir pressure,well parameters,formation parameters and water production,while sulfur deposition and stress sensitivity have little effect,but the influence of sulfur deposition and stress sensitivity should not be neglected in later production period.Therefore,it is necessary to take into account the influence of various factors,and adjusting the development plan in time can prolong the stable production time of gas wells3.A mathematical model of horizontal well seepage in high-sulfur fracture bottom water gas reservoirs is established,in which sulfur deposition in fractures near wellbore,bottom water invasion and stress sensitivity are taken into account.The numerical simulation program is compiled by using MATLAB,and the simulation calculation is carried out using domestic high sulfur gas reservoir data.The reliability of the model is verified by comparing with the mechanism model established by ECLIPSE.4.Based on the seepage mathematical model and the mechanism model established,the simulation results show that:(1)The size of water body mainly affects the stable production time and the rising rate of water-gas ratio after water breakthrough.The larger the water body of gas reservoir,the shorter the stable production time,the larger the cumulative water production,the faster the water-gas ratio rises.(2)Sulfur deposition reduces the seepage space near the wellbore,increases the skin factor of gas wells,reduces the stable production time of gas wells and slows down the rise of water-gas ratio,which indicates that sulfur deposition can reduce the flow of gas and water phase at the same time.(3)The ratio of fracture to matrix permeability has a great influence on the stable production time,water breakthrough time and the rising speed of water-gas ratio.The bigger the ratio of fracture to matrix permeability is,the easier bottom water invade into gas reservoir through fracture,resulting in shorter stable production time of gas wells,earlier water breakthrough time,faster rise of water-gas ratio and more cumulative water production.(4)The size of production has a great influence on the stable production time and water breakthrough time of gas wells.The larger the production,the shorter the stable production time of gas wells,the earlier the water breakthrough time,the faster the water-gas ratio rises,and the larger the cumulative water production.However,too small of the production is not conducive to fund recovery,so it is necessary to control the production reasonably.