考虑海底增压的深水钻井当量循环密度预测方法

Prediction method for equivalent circulating density of deepwater drilling when subsea pressurization is considered

针对深水井筒ECD预测与控制方面存在的不足,建立了考虑温度和岩屑影响及有海底增压管线举升系统情况下的深水钻井ECD预测模型,以实例计算分析了深水钻井中有海底增压管线举升系统情况下ECD变化。结果分析表明,钻柱内的排量一定时,增注排量越大,ECD值越小;在有海底增压管线举升系统时,本计算条件下ECD值均未超过漏失压力,因此该种参数工况下应该为安全状况;在无海底增压时,随着排量的降低,环空ECD逐渐增加,且ECD增加值较大;当排量小于一定值时,ECD的增加会导致在钻井过程中的地层漏失。因此在深水钻井过程中应该特别注意在隔水管段的井眼清洁问题,除了控制机械钻速、泵入清扫液等措施以外,还应适量采取增加排量来及时清除钻屑,保持井眼清洁。最后对比分析了模型的有效性,在本计算条件下与PWD实测值偏差最大1.36%,对深水钻井水力参数优化设计及井控具有一定的参考意义。

Considering the shortcomings in ECD prediction and control of deepwater wellhole presently, the ECD prediction model of deepwater drilling has been established, with the temperature and rock debris effects are considered and the lift system of subsea pressurization pipeline is provided. The ECD changes are calculated and analyzed based on the living examples, when the lift system of subsea pressurization pipeline is provided in the deepwater drilling. According to the results, when the displacement in the drilling string is constant, the larger the augmented injection displacement, the smaller the ECD value; when the lift system of subsea pressurization pipeline is provided, the ECD value under such calculation conditions does not exceed the loss pressure, so it should be safe under such parameter conditions; when no subsea pressurization exists, as the displacement decreases, the annular ECD gradually increases, and the ECD added value is relatively greater; when the displacement is less than a constant value, the ECD increase will lead to the stratum loss during the drilling. Therefore, during the deepwater drilling, special attention should be paid to the borehole cleaning at the riser section. In addition to the control over mechanical drilling rate, pumping of cleaning lfuid and other measures, the displacement should be appropriately increased to clear the drilling cuttings in time, which is in order to keep the borehole clean. Finally, the model validity has been compared and analyzed. Under such calculation conditions, the maximum deviation from actually-measured value of PWD is 1.36%. This method has certain reference signiifcances for the optimization design of hydraulic parameter on deepwater drilling and well control.