A Reaserch On Reservoir Geomechanic Features Of A Gas Storage In Xinjiang After Natural Depletion

The building and operation of underground gas storage after reservoir depletionis a comprehensive technique. In this paper, on the basis of conventional geologicalresearch, the study including stress-strain characteristics and seepage characteristicswhich effect gas storage rebuilt is carried out. Using FMI well logging data, in-situstress of the work area has quantitative evaluated, pore pressure, collapse pressure,and fracture pressure profile of reservoir has constructed. On the basis of physicalproperty analysis in well logging interpretation, using the well test analysis wascarried out in order to understand the physical characteristics changes alongdevelopment with the change of pore pressure, and further quantitatively determinesthe permeability change, which effects the injection&production capacity while gasstorage operating. Using stress coupling numerical simulator to forecast the porepressure change according to the injection scheme, the stress change caused by porepressure will not damage the faults stability and crack also won’t appear under thecondition of the recommend scheme.This research also introduce a new simulation technology which integratedreservoir model, well model, and surface gathering model together to predict theproduction performance for gas storage. This integrated application is the domesticfirst time for gas storage. This integrated model coupling the gas reservoirengineering problems and the physical problems such as stress and strain relationscaused by development process together to carry out simulation and forecast of theKPI of gas storage, this paper focuses on analyzing the variation of pore pressure ingas storage operation, crack, water invasion, load of gas storage capacity and theKPI of gas storage operation.Main conclusion:Long-term depletion influence physical properties of researvoir and reduce wellproductivity because of permeability decreased. SH_MAXof in-situ stress direction isN23°. The gas bearing layer’s pore pressure is lower to13.7MPa, the fracturepressure is57MPa. In order to prevent break through two main fault zone and cap,the critical reservoir pressure should be less than69.16MPa, the cap breakthrough pressure is49MPa. Recommendations can be on the premise of meet therequirements of gas storage load regulation, to ensure the safety of the reservoirin-situ stress during operation and no cracks appearence.This Gas storage is in better control of edge-bottom water effect on the current.Water influx cause reservoir damage in this area therefore, gas injection to drive theedge-bottom water to expand the capacity of gas storage shall not apply in this area.When work volume of the gas storage is45.1×10⁸m³, reservoir capacity is upto127.7×10⁸m³, which greater than the design capacity of107×10⁸m³. Gasreservoir pressure is up to30.38MPa, which less than the design pressure of34MPa.Further simulation results show that when gas reservoir pressure rise to34MPa, theupper limit storage capacity will be145×10⁸m³.The upper productivity is2535×10⁴m³/d, the lower gas production is252×10⁴m³/d. The upper productivity of each well is from35×10⁴m³/d to314×10⁴m³/d。Through this study, the stress numerical model of the work area is established;the quantitative research of reservoir physical properties change and its impact onproduction capacity of gas storage is researched.The integration of numerical simulation methods has been introduced forsimulate the key production index of gas storage operation. The study also providesa strong technical support for gas storage operation scheduling research. Theintegrated model also can be a monitor for safe operation to ensure the long-termoperation of the gas storage.