关键词: 固井, 工作液密度, 力学模型, 水泥环, 套管, 界面胶结强度, 应力计算式

Abstract:

The density reduction of operating fluid after well cementing may cause many problems such as disturbing the relation between cement sheath and formation, developing micro-annulus, disabling interlayer isolation of cement sheaths. The thick-walled cylinder theory was used to establish a casing-cement-formation mechanical model favorable for bearer features of cement sheaths. The formulas for describing displacement and stress of cement sheath were obtained when the density of operating fluid reduced during work after well cementing. Analog calculation showed that at the same well depth, the more value of density reduction would result in the bigger value of stress cement sheath. When the value of density reduction was same, the smaller well depth would result in the smaller value of stress cement sheath. By combining results of analog calculation and cementing strength between cement and simulated casing, a new technical means was proposed to prevent micro-annulus fractures. Selecting and designing different slurry system and reducing the value of fluid density can prevent the interface cementation from generating micro-annulus.

Key words: well cementing, density of operating fluid, mechanical model, cement sheath, casing, surface cementation strength, stress calculation formulas