【名词&注释】
钻井液密度(drilling fluid density)、节流阀(throttle valve)、发信号、压井液密度(well killing fluid density)
[单选题]井深H=5000m,气侵前钻井液密度rm=1.20g/cm3,气侵后返至井口的钻井液密度rs=0.60g/cm3,Ps=0.0981MPa,井底钻井液柱压力减少值为()。
A. 5.470MPa B. 0.670MPaMPa C. 0.630MPa D. 0.627MPa