Bottomhole pressure control technology in underbalanced drilling;

The prediction technology of hole enlargement ratio in the condition of underbalanced drilling;

The new well control device for underbalanced drilling process;

Gas acquisition and interpretation & evaluation under under-balanced drilling;

Effect of annular cuttings on negative pressure in under-balanced drilling process;

Practical drilling fluid technology for under-balanced drilling;

Study of free clay phase oil in sea water drilling mud used in under balanced drilling;

Therefore, using aerated drilling fluids and under balanced drilling techniques can not only meet with the geologic requirements but also ensure the normal drilling.

Low density drilling fluid is used for under balanced drilling.

A brief analysis of mud logging operation during underbalance drilling;

Some forward requirements for the identification and evaluation of geological logging with drilling gas-bearing reservoirs have been carried out by the application of underbalance drilling technology.

While underbalance drilling spreads greatly, rotating blowout preventer, as a kind of high technical product, is the crucial equipment to control well pressure.

Using under balance pressure drilling technique aims at preventing the mud loss and pollution of Palaeozoic limestone reservoir in this area and therefore protecting oil reservoir.

It is discussed that the feasibility and necessity of under balance pressure drilling technology using in coalbed gas development in China,considering the characteristics of coalbed gas reservoir and coalbed gas well in China.

Selection of cutting carrying medium is very important for unbalanced drilling,which should protect oil & gas reservoir and keep the borehole stability.

To solve these technical problems,research work on wellbore optimization,bit selection,unbalanced drilling,high-pressure jet drilling were conducted.

To ensure safe drilling and protect reservoir, through research and optimization of the unbalanced drilling technology, the "offshore pressure-controlled drilling technology" is put forward, the focus of which is to realize micro-overbalanced drilling by using unbalanced drilling equipment, lowering drilling fluid density, and adjusting the wellhead casing pressure.