Study On The Technique Of Solidifiable Plugging Fluid For The Fractured Lost Circulation Formation

Lost circulation is one of the most serious problems in petroleum industry.The lost circulation will be subject to consequences ranging from affecting the drilling time to causing security incidents.Lost circulation in fractured formation is an issue with far-reaching effects and can lead to most serious consequences.So the study of lost circulation in fractured formation is imperative.Firstly,based on the analysis of internal and external causes of the lost circulation in fractured formation,one can draw a conclusion that "plugging to prevent lost circulation".Aiming at the shortcomings of the technologies on the fractured formation,the plugging fluid should contain three functions:bridge plugging(physical plugging),retaining in the fracture,cementing plugging(solidifiable).The characteristics of plugging fluid have been proposed:being unpolluted by mud,bridge plugging the formation to prevent fluid leakage,washed away hard and curing to cementing the crack,and on the basis of previous research.Secondly,according to designed characteristics of the solidifiable plugging fluid,the mechanism on this fluid was studied.Based on the bridge plugging and the width of crack,the mechanism on physical plugging of the was formed.Two bridge plugging materials were determined,and physical plugging could bear pressure more than 6 MPa for 1-2 mm crack.The mechanism of stopping in the(strong thixotropic)was studied,and thixotropic agents was used to give the fluid this ability.Slag and diatomite were used to give fluid solidification capacity.For purpose of the solidifiable mechanism of the fluid,TG?heat of hydration?XRD?SEM and EDS were used.It shows that the basis of solidified subject is layered rod-like I C-S-H(CSH),in which the part of Si4+ is replaced with Al3+.Thirdly,based on the plugging mechanism and the need of working liquid stabilization,stable agent,weighting agent and dispersed agent were selected.The rheological properties of the fluid,density and compressive strength of solidified subject were regarded as the object of research.Through differences of three objects on the different conditions,a set of solidifiable plugging fluid(1.3g/cm-2.1g/cm3)was selected,which conformed fully to design requirements.Finally,engineering properties of the solidifiable plugging fluid were evaluated.The safety thickening time of the solidifiable plugging fluid was all more than or equal to 360 min.The time can fit most plugging construction.The mud pollution experiment showed that the mud would reduce the normal temperature fluidity and compressive strength of the working.Meanwhile the mud would also extend the curing time,but the time can be adjusted by the amount of activator.Through the simulation test device of the plugging on the HTHP leakage formation,the actual bearing capacities of solidifiable plugging fluid was evaluated.It showed that the actual bearing capacities of 1.5 g/cm3 solidifiable plugging fluid was 7.8MPa(2d),and it positively related to the compressive strength.Combining with the compressive strength of the solidified subject after 1d?2d and 7d,long-term bearing pressure capacity of the work liquid were evaluated.The results showed that curing strength increased over time,and long-term bearing pressure capacity of the work liquid can be guaranteed.The research results of the paper provide later researchers with a theoretical reference,and also provide a guarantee for the success of plugging and long-term bearing pressure capacity of the formation.The research of this paper has profound meaning in controlling effectively or even solving the leakage problems.