Then breakdown pressure,caving pressure and drilling fluid density can be obtained,which will act as references for drilling design to guide safe drilling.

Based on logging data and the results of formation fracturing tests, a set of methods of calculating the caving pressure and related physical and mechanical characteristic parameters of formation are established.

Based on the comprehensive analysis of some complicated situations met in drilling,such as circulation loss,borehole shrinkage and collapse,the collapse pressure and fracture pressure of the drilled well interval were determined.

The well collapse pressure of extended reach well and the security density window of drilling fluid was estimated based on the Coulomh-Moore strength criteria and the maximum tension stress fracture criteria.

Water-base drilling fluids usually increase shale collapse pressure, different drilling fluid system brings different increase degree of collapse pressure.

The results from contrasts of collapsing pressures between unhydrated shale and hydrated one indicate that collapsing pressure for shale which behaves poor water sensitivity can be increased on a large scale,and verify the phenomenon exists that shale is stable in early contact with drillng fluid and turns out to be unstable later.

Pore pressure,breakdown pressure and collapsing pressure are the bases of determining the casing programme,drilling fluid density and cementing and completion plan,and are important in the design of drilling engineering.