深水钻井热交换作用下的井壁稳定性分析

Analysis on stability of borehole under the effect of heat exchange in deepwater drilling

为了研究深水钻井过程中热交换作用对井壁稳定性的影响规律,建立了钻井液、钻柱、海水和地层各介质热交换作用下温度控制方程,根据热弹性理论计算温度变化对井周应力的影响,结合地层强度准则与拉伸破坏准则确定深水井壁坍塌压力与破裂压力。结果表明,钻井液循环对地层产生的冷却作用能够降低井壁坍塌压力与破裂压力,但破裂压力降低幅度比坍塌压力的降低幅度稍大。因此,尽管钻井液的冷却效果能够抑制井壁坍塌,但应注意低温度的井壁更易形成诱导缝,甚至引发地层漏失。计算结果对深水钻井作业具有指导意义。

In order to study the influence of heat exchange on the stability of borehole in the process of deepwater drilling,the temperature control equations of various mediums,including the drilling fluid,drill pipe,sea water and formation,under the effect of heat exchange were set up. The influence of temperature change on the stress around wellbore was calculated according to the thermal elastic theory,and the collapse pressure and fracture pressure of deepwater borehole were determined combining with the formation strength criterion and tensile failure criterion. The results showed that the cooling effect of drilling fluid circulation on the formation can reduce the collapse pressure and fracture pressure of borehole,but the reduction extent of fracture pressure is slightly larger than that of collapse pressure. Thus,although the cooling effect of drilling fluid can inhibit the borehole collapse,it should be noticed that the induced fractures happen easily on the borehole with low temperature,even cause the formation leakage. The results have a guiding significance for the deepwater drilling operation.