Under-balanced drilling has the advantage of improving the drilling rate,reservoir protection,outstanding advantages of oil and gas reservoir,but the ground water gushing and borehole instability have seriously impeded the generalization of under-balanced drilling.The conventional methods of Wall-Protecting And Leakage-Plugging can not meet the requirement of gas drilling technique any more;on the other hand,the introduction of chemical grouting technology will become an effective way to solve the technical problems.Chousing the formamide as hardening agent,the gelation action of sodium silicate and Formamide in high temperature has been analyzed.The research has got a new chemical grouting material which characterized by high temperature resisting,well groutability,controllable gelation time under high temperature and high compressive strength of consolidating body.It can be used for gas under-balanced drilling in the complex formation of wall-protecting and leakage-plugging.

Gas drilling has been widely used in northeast Sichuan area gradually.It not only can greatly increase the penetration rate,shorten the construction cycle,reduce drilling costs,but also can improve the rate of exploratory wells and enhance recovery ratio.Anticipating the complex characteristics of gas drilling in the course of drilling,using the immediate symptoms during before or during the accident occurred to forecast and treat down hole accidents timely is key of gas drilling.The paper summarized some symptoms of yielding water,borehole collapse and hole deviation in northeast Sichuan area by practice.Meanwhile,the method on how to diagnose complicated downhole problems according to these symptoms was described,and some processing methods on formation water output,hole sloughing,borehole inclination and so on were put forward.

The dynamic features of bottom hole assembly(BHA) and mechanism of borehole deviation in air drilling were studied using slick drill collar.The dynamic model for rotor of slick BHA was established.The dynamic features of BHA under the conditions of mud fluid were compared to those of air drilling.The results show that the higher friction coefficients of borehole wall can result in a backward whirling motion of the BHA and lower damping coefficient of air makes the whirling speed higher in air drilling.The BHA in mud fluid drilling can whirl forward at a lower speed,due to the lower friction coefficients in the wall of borehole and higher damping coefficient of mud.The comprehensive function of these dynamic features made a smaller deviation dropping on bit in air drilling than that in mud drilling,which leads to the deviation of drilled borehole in air drilling.

Air drilling has two advantages of increasing ROP and formation protection, and the air drilling is developed rapidly in China. With the air drilling, a lot of new oil and gas resources have been discovered. Although the air drilling has its advantages, the limitations of the air drilling process must also be regarded. The technology of air drilling had improved rapidly with the air drilling was taken into account by the petroleum industry, but excessive formation water, wellbore stability, sulfide formation, downhole fire etc. issues have restricted the air drilling. Integrating the field trial in SuLiGe area of ChangQing, the paper analyses the complex condition accompanying air drilling and have formed a series methods dealing with the complicate problem in air drilling.