欠平衡钻井中钻井液密度的确定与控制方法

DETERMINATION AND CONTROL OF THE DENSITY OF DRILLING FLUIDS DURING UNDERBALANCED DRILLING

合理的钻井液密度是欠平衡钻井安全、快速施工的前提。在欠平衡钻井工艺方面 ,研究较多的是井壁稳定力学和油气储层保护 ,在确定和控制井底负压差及钻井液密度方面研究较少。讨论了欠平衡钻井井底负压差的确定因素和合理钻井液密度的计算方法 ;研制出欠平衡钻井地面数据监控系统 ,可依据实时监测的钻井作业参数和产出流体量 ,以及立管压力和套管压力与井底实际压力间的数学关系及软件计算 ,调节钻井液密度和井口回压来控制井底负压差。理论模式和控制方法经计算模拟及现场应用 ,符合钻井现场要求 ,软件计算误差小于 5%。

As a new technology served to exploration and development of oil field s, underbalanced drilling technologies have been developed rapidly in China and overseas. However, only little studies of design theories and control techniques on bottomhole negative differential pressure were conducted. In this paper, the determining factors of bottomhole negative differential pressure and calculatio n methods of drilling fluids during underbalanced drilling are described in deta il. Simultaneously, several practical approaches controlling bottomhole negative differential pressure and the density of drilling fluids during underbalanced d rilling are discussed. The theoretic models and control approaches provided in t he paper have been successfully applied in several oil wells with the technology of underbalanced drilling.