深水浅层呼吸效应机理及影响因素分析

Analyses of the Ballooning Effect and its Affecting Factors in Drilling Shallow Formations in Deep Water

对地层呼吸效应误判为井涌而采取压井措施容易造成恶性漏失,会提高深水作业的风险与成本,对深水钻井的安全高效造成了严重的危害。因此,对深水浅层呼吸效应机理开展研究,并利用COMSOL软件,模拟深水浅层钻井过程中呼吸效应的全过程,研究地层特性、钻井液性质和压差对呼吸效应的影响。模拟结果表明,深水浅层呼吸效应属于渗透性机理;低弹性模量、低泊松比、高孔高渗地层极易发生渗透性呼吸效应,而使用高黏度、高动切力钻井液,采用小压差(低密度钻井液、低排量等)形式钻进,有利于抑制呼吸效应的程度。因此,在低弹性模量、低泊松比、高孔高渗地层钻进时,需提前做好措施,如加入降滤失剂、降低泵速等,以减少地层呼吸效应带来的影响。研究成果能为深水浅层呼吸效应判别及预防和控制方案提供一定参考。

Ballooning effect encountered during drilling is easy to be taken as well kick and the well is then killed.This operation often results in severe mud losses,increasing the risks and costs and causing serious harm to the safety and efficiency of deep-water drilling.To solve this problem,the mechanisms of ballooning effect was studied,and the COMSOL software was used to simulate the whole process of ballooning during drilling in the shallow formations in deep water area.The effects of formation characteristics,drilling fluid properties and pressure differential on the ballooning effect were studied.The simulation results have shown that the ballooning effect taking place in the shallow formations in deep water area is a permeable mechanism.The permeable ballooning effect is very easy to happen in formations with low elastic modulus,low Poisson’s ratio,high porosity and high permeability.This kind of ballooning effect can be inhibited with high viscosity high yield point drilling fluids,and drilling with low pressure differentials(low density,low flow rate).Thus,when drilling formations with low elastic modulus,high Poisson’s ratio,low porosity and high permeability,measures should be ready in advance,for example,treating the mud with filter loss reducers,reducing pump rate,to minimize the impact of the ballooning effect.This study is of reference importance to the identification,prevention and plan for the controlling of ballooning effect encountered in shallow formations in deep water area.