Analysis Of Conditions And Criteria For Tie-back Liner In The Deep Well Casing Program Design

In the casing program design for deep well drilling, using drilling liner cannot onlycontribute to increase the rate of penetration, but also reduce the cost of drilling. However,whether drilling liner should be tied back is not clear when continue drilling after it iscemented. Little research has been down on the conditions of tying back liner. The criteria ofcasing program design are not given which are conducive to high-pressure gas well controland early gas kick detection. Therefore, the study on effects of changing wellbore horizontalsize after tie-back liner is significant in order to gain conditions and criteria of tie-back it andinstruct whether tie-back it in the casing program design.Considering the effect of varying annular cross sections, a two-phase flow model basedon drift flux model is established to describe gas kick. The model is solved by finitedifference method. Then wellbore pressure calculation software is developed using vb.netprogramming language, which is mainly comprised of parameter input module, kicksimulation module, well killing simulation module and circulating pressure loss calculationmodule. The software can simulate the whole process of gas kick to blowout, as well as wellkilling process after the well is shut in when pit gain reaches to a certain degree, andtwo-phase flow parameters can be given at any time and any spatial domain during thesimulation process. The software has been tested by field data， and results show a goodagreement with actual data.A work has been down to analyze the impact of casing program change on the annulustwo-phase flow and well control through tie-back liner. Several variations (the bottom holepressure, pit gain, the discovery time of gas kick and gas holdup) have been mainly studiedduring the gas kick while liner is tied back at different height. The same work has been downon variations such as casing pressure and casing shoe pressure during well killing process. The results show that the discovery time of gas kick is reduced after drilling liner is tied backto the wellhead which is conducive to the early detection of gas kick; the casing pressure peakincrease during the killing process, meanwhile the internal pressure strength of intermediatecasing increase which ensure the safety of killing.Factors are given such as the initial bottom hole pressure difference, permeability,porosity, killing displacement and pit gain that may influence the casing pressure, and mainfactors which are crucial to the casing pressure are found. The circulating pressure loss iscalculated after tie-back liner. The conditions to tie-back liner are analyzed after consideringboth advantages and disadvantages of tie-back liner. Finally, four typical deep well casingprograms are summarized and conditions of tie-back liner are analyzed. The research showsthat it is not necessary to tie-back liner if formation pressure prediction error is less than10%and the well can be shut in before the pit gain reaches to10m3.