Analysis Of The Effect Of Sulfur Deposition On Gas Deliverbility

Since the growing demand for natural gas, exploitation of sour gas reservoir has become an important topic. Yuanba field is another important field following Puguang gas field exploited by Sinopec,the exploration of which will contribute a lot to the supply of natural gas as well as the sustainable development of economy in Sichuan, Chongqing and the Yangze River region. The deposition of elemental sulfur is one of the most difficult problems faced during sour gas reservoirs mining. As the mining process goes on,the elemental sulfur will decrease along with the reduction of temperature and pressure.Elemental sulfur will accumulate to be liquid or solid phase in the stratum leading to clog of pore space through which the gas flows as well as the decrease of porosity and permeability. The productivity will be negatively affected and in some worse situations the production will be shut down. In order to ensure efficiency,safety and rationality during exploitation of the wells,it is necessary to carry out a further comprehensive research about the internal relation between deposition of sulfur and productivity of the well. The research will provide technical support and theoretical guidance to the initial mining and subsequent exploitation of Yuanba gas field.Changxing Formation of yuanba gas field has the characteristics of deep burial with high level both in temperature and pressure,high content of the hydrogen sulfide, partial water seepage, crack–pore structure,controlled by the reef body. Based on the knowledge of geological characteristics and previous studies consist of geological data, productivity reports,PVT experimental data and other information in the area,I calculate and analyze the sulfur phase,fluid physical parameters,sulfur solubility. The results show that if sulfur deposition happen since Yuanba Changxing the aggression of sulfur will be in a liquid phase. For Yuanba Changxing gas reservoir I got the corresponding deviation factor, the viscosity and solubility calculation empirical formula using conventional methods and with the help of VB programming I calculated non-hydrocarbon corrected deviation factor and viscosity. I did a series of comparative analysis of the error in the experimental values to optimize computing methods. The formula to calculate solubility is a correction of classic Chrastil empirical relationships based on actual experimental data of YuanbaChangxing gas field while using piecewise calculation for the density of the turning point. Finally I came up with an empirical formula of solubility for yuanbaChangxing gas reservoirs which significantly improves accuracy of calculation.Darcy and non-Darcy sulfur deposition forecasting model are widely used to predict sulfur deposition.Compared with Darcy flow model,Non-Darcy flow modeltakes the influence of non-Darcy flow velocity and density into consideration which leads to a higher sulfur saturation more and ultimately in line with actual production.The model is able to predict sulfur saturation in certain produce time and a certain radial distance,which is of great guiding significance to decidethe timing and location of sulfur elimination. The prediction results disclose that near wellbore area is more prone to sulfur deposition,the shorter the radial distance from the wellbore,the longer production time, the more serious the sulfur deposition. Base on sensitivity analysisabout distribution of sulfur saturation, such as porosity, permeability, effective thickness,yield and so on.It reveals that the sulfur saturation increase in proportion of production while in inverse proportion of porosity,permeability,effective thickness, which will result in lager occurrence probability of sulfur deposition. Separately using the two districts composite productivity equation and Schedule skin sulfur deposition coefficient method to predict the impact of sulfur deposition on productivity.As a result,it shows that sulfur deposition causes the increase of well skin and decrease of gas production capacity. If the sulfur deposition is resolved,the gas productivity will increase. However, due to the geological characteristics of the region and the damagecaused by liquid sulfur the formation damage and deposition of sulfur capacity will not be serious in early production stage in YuanbaChangxing gas field.Considering that Yuanba Changxing gas reservoir is a sour gas reservoir with high reserve, it is better to drill small number of wells on the premise of high productivity. And horizontal wells and highly deviated wells are highly recommended. On the basis of conventional horizontal well productivity equation this report added the effectsof fractures and sulfur deposition, established fractured sulfur horizontal well productivity equation,and analyzed the impact of sulfur saturation, fracture permeability,horizontal length for the flow well productivity.The conclusion is the greater the degree of sulfur saturation is,the lower well productivity is; If fracture permeability is larger,the length of the horizontal section is longer, the productivity of sulfur fractured horizontal wells will increase. It is of great importance to guide a reasonable allocation of the production, acid fracturing,horizontal drilling and so on.