深水钻井密闭环空圈闭压力预测及释放技术

Confined Annular Trap Pressure Prediction and Release Technology for Deep Water Drilling

深水油气资源勘探开发中,由于水深的影响,海底及浅部地层温度低,而储层流体的温度相对较高,在钻井以及生产阶段,井筒内的钻井液或油流的温度明显高于浅部地层的温度,这样就导致套管柱各层套管之间环空的流体温度升高,如果各层套管之间的环空是一个密闭空间,必将导致压力的升高,压力升高到一定程度就存在挤毁套管的风险。因此,密闭环空的圈闭压力是深水开发钻井套管柱设计中需要考虑的必要因素。分析了环空圈闭压力升高的影响因素及计算方法,敏感性分析表明,油藏的初始静态温度、流体类型和生产流速、流体的特性、水泥浆封固位置对环空圈闭压力的影响较为明显。结合西非某油田实例,介绍了常用的释放环空圈闭压力的方法和现场应用效果,确定提高套管强度、套管设计中使用破裂盘、使用尾管代替套管和可压缩性泡沫材料,能有效释放密闭环空压力。

The exploration and development of oil and gas resources in the deep water,the temperature of sea bed and shallow strata is low,but the temperature of reservoir fluid is relatively high,so the temperature of drilling fluid or flow stream in bore hole is obviously higher than the temperature of the shallow strata at drilling and production stage,which leads to higher temperature of annulus fluid between each casing.If the annulus space between each casing is closed,the pressure must rise.When the pressure rises to a certain extent,there is a risk of casing failure,so trap pressure of the confined annular space is a necessary factor when casing string in the deepwater development is designed.In this paper,the influence factors of elevated annular pressure and the computing method of annular pressure are analyzed.Sensitivity analysis shows that initial static temperature of oil reservoir,fluid type and production flow velocity,fluid characteristics and seal position of slurry have obvious effect on the annular trap pressure.Based on the case of some oilfield in West Africa,common method for releasing the annular trap pressure and its field application are introduced.It is effective through improved casing strength,rupture disc used in casing design,the application of tail pipe instead of casing and compressible foam material.