注气欠平衡钻水平井技术面临的两大技术难题是井下动力钻具不能正常工作和常规MWD无法正常工作。

The two technical problems faced by the technology of under-balanced horizontal well drilling with gas injection are the down-hole motor and the conventional MWD can't work normally.

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在数值技术方面，隐式积分方法被用来对本构方程的局部时间积分，动力显式技术用于求解总体平衡方程。

For the numerical aspects, an implicit integration scheme is used for local time integration of the constitutive equations and a dynamic explicit scheme is used to solve global equilibrium equations.

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