底水气藏水侵规律数值模拟研究:以元坝长兴组气藏为例

Numerical simulation of water intrusion in wet gas reservoirs:A case study of the Changxing gas reservoir in Yuanba

有水气藏开发过程中,边底水的侵入严重影响气井产能,但是目前对底水气藏水侵规律缺乏深层次认识。为此,基于元坝长兴组气藏2类产水气井生产特征,结合气藏实际地质特征、水体性质及气-水界面关系,分别设计直井和水平井水侵机理数值模拟模型,重点分析采气速度、水体大小、致密层连通性及避水高度等因素对生产及水侵影响规律。研究结果表明:(1)采气速度是影响水侵的主要因素,水体一定,采速越高,水侵越快,气井稳产期越短,水平井在一定程度上能有效抑制水侵;(2)水体大小是影响水侵重要因素,水体倍数越大,水侵越严重,气井稳产期越短;(3)致密性夹层能在一定程度上抑制水侵,渗透性夹层(Kiz=100%Kz)对应的底水锥进速度最快,稳产期最短;(4)随着避水高度的增加,水气比上升变缓,气井见水时间变晚。结论认为:对于底水气藏,保持合理的生产压差或优化配产是控制底水快速锥进的关键;若储层中天然致密层无效,则可通过建立较低垂向连通性的人工隔夹层(致密夹层)抑制底水锥进;同时,钻井设计或后期补射孔时,需兼顾射开程度和避水高度对生产的影响。本文研究成果以期为底水气藏高效开发提供理论指导。

The intrusion of edge and bottom waters in water drive gas reservoirs can severely impact the production capacity of gas wells;however,the law of water intrusion in wet gas reservoirs is not well understood.To fill this knowledge gap,the production characteristics of vertical and horizontal wells drilled through the Changxing Formation in the Yuanba gas field is investigated in combination with regional geological conditions,water properties and gas-water interfacial relationship to establish a mechanistic model of water intrusion via numerical simulation,and the influencing factors of gas production and water intrusion such as gas production speed,water body size,tight layer connectivity and height of water avoidance are analyzed.The results show that(1)the gas production speed is the main influencing factor of water intrusion as higher production speed leads to faster water intrusion and shorter stable production period,while the horizontal well can effectively inhibit water intrusion to a certain extent.(2)The size of the water body is another important influencing factor,the larger the water body size,the more serious the water intrusion and the shorter the stable production period.(3)The tight interlayer can inhibit water intrusion to a certain extent,and the bottom water cone,corresponding to the permeable interlayer(Kiz=100%Kz),has the fastest advance speed and the shortest stable production period.(4)As the avoidance height increases,the water/gas ratio increases slowly and water intrusion is delayed.Therefore,for water drive gas reservoirs,maintaining a reasonable production pressure difference or optimizing production practice is the key to controlling the rapid coning of bottom water.If the natural tight layer in the reservoir is ineffective,the submersible water cone can be inhibited by establishing an artificial compartment(dense interlayer)with low vertical connectivity.At the same time,when designing well drilling or later replenishing holes,it is necessary to take into account the impact of the injection hole size and height of water avoidance on production.The results of this study can be used to guide the development of submersible wet-gas reservoirs.