A Study On Predicting Formation Water Production And Wellbore Stability For Gas Drilling In Daqing Oilfield

In Daqing oilfield, deep formation of Daqing oilfield, the drilling ability in deep formation below QuanTou group is very high and reaches to 6~9 grades, The Rock hardness is 750~2500 MPa. In order to improve ROP, In order to improve ROP, the air /foam drilling field test was carried out in Quantou Group and below formations of the deep Cretaceous in 2005. The ROP was increased distinctly obviously and was more 3~5 times of than the conventional drilling. But however, the borehole instability, drill pipe sticking, string failure and other complicated incidents occurrences caused by formation water production sometimes occur occasionally happened. Several wells could not drill to the target depths design depth (TD) because of due to formation collapse of in fractured volcanic formation. The problems of borehole instability and formation water production affect the ROP, quality and cost of air/foam drilling, These inhibit the advantages of the gas drilling gas/foam drilling.On the base of linear pore elastic theory, taking the impact of pore pressure and porosity into account, this paper established the borehole stability prediction model that was suitable for gas drilling in deep formation of Daqing oilfield. The empirical parameters in the prediction model were regressed too. These can provide criteria for predrilling borehole stability evaluation of gas drilling and the feasibility evaluation of gas drilling operation.This paper has established the qualitative identification methods of formation water production layers and the quantitative calculation model of formation water production under the condition of dynamic non-steady flow in gas drilling in Daqing oilfield. During gas drilling, these solved the key technologies of water lays identification and the quantitative calculation of water production, provided the theoretical basis for optimizing well placement and lays selection and drilling medium transformation, avoided or reduced borehole instability, sticking, string failure caused by the complex problems and so on. All of these are helpful to assure the optimization of design program and safe operation for gas drilling.