Research On The Integrated Cementing Technology Of The Second Interface Of Cementing

In recent years,with the devolepment of gas exploitation in Tarim oilfiled,more and more problems are encountered.Sustained casing pressure?SCP?have been detected after intermediate casing or production casing cementing in more than 90 gas wells according to statistics.Weak bonding of cement to formation is responsible factor to account for zonal isolation failure and SCP.The key reason for this problem lay in unsolidified drilling fluid and filter cake that formed between cement sheath and formation during drilling process.At present,universal fluid?UF?and mud to cement?MTC?have been the main technologies since engineers have recognized its importance.But the relative research and application is just a flash in the pan.The reasonable factors as follows:?1?UF has been limited to used in shallow?average depth<2000m?,low temperature?average temperature ?70??wells.Research and application density lower than 1.30g/cm³;?2?As potentially active materials,the negative influence of blast furnance slag?BFS?on UF properties hasn't been researched particularly,although it has been regarded as none-influence;?3?The main purpose of MTC is designed to a replacement of cement to cementing.But its high temperature intolerance significantly restrict its application area.To obtain well bonding of cement to formation,the theory of UF and MTC is referenced.A solidified filter cake mud?SFCM?and solidified speacer was reasarched in this article.This research is aim at the second section?average depth ?5000m?cementing of gas wells of Kuqa depression in Tarim oilfild.Sulphonated polymer mud was prepared according to KS8 drilling engineering design.Two different BFS were mixed and added in sulphonated polymer mud to form the SFCM.Daily property evolution of SFCM during a long-term stiring under condition of 70?,95?,108?,120? was tested.Results demonstrate that properties of SFCM remained stable under condition of 108? and 120?,while got worse under condition of 70? and 95?.But the variation can be controlled by adding addtives to maintain an acceptable properties.A cement-formation interface model was made by artificial core,SFCM fiter cake and different cementing fluid including cement slurry,solidified speacer and their mixture.Shear strength was tested to evaluate filter cake and improvement of bonding quality.Results shows that the shear strength could reach to 0.75-1.35MPa when filter cake thickness less than 1mm,which distinctly higher than the un-solidified one.XRD phase identification was used to analyse filter cake.C₃S?C₃A and aragonite was detected in un-solidified fiter cake containing BFS.It's indicate that slight hydration of C₃S?C₃A occurred during long-term stiring,and the hydration process leaded to properties variation of SFCM.In contrast,the phase composition of solidified filter cake reviews significant change.Calcium silicate hydrate C-S-H,tetracalcium aluminate hydrate C4AH13,gehlenite C₂ASH₈ and tiny ettringite 3CaO·Al₂O₃·3CaSO₄·32H₂O were detected.SEM was used to observe filter cake's structure.Images acquired by 1000× shows the loose structure in un-solidified filter cake.Barite and bentonite scatters among it.Images acquired by 5000×shows a very clear edge and boundary between solide particles.In contrast,the structure of solidified filter cake are completely different.The edge and boundary of BFS particles disappears due to its hydration.Barite and bentonite are wrapped by hydration products.Interspace between particles are filled by hydration products.More importantly,lots of fibroid hydration product what was confirmed as C-S-H gel by XRD was observed in 5000× Images.It's precisely the exists of C-S-H gel that net structure is formed and solide particle are bonded to each other.Along the hydration,the C-S-H gradually hardened from gel to solid.Then the filter cake solidified,too.Similarly,the C-S-H also formed in cement or solidified speacer as the hydration of filter cake go along.Thus,with the C-S-H permeating into each other,the bonding quality of second interface improved.The advantages of this method,which could be applied in deep?maximum depth<5000m?,high temperature wells?maximum temperature ?120??,has been proved by laboratory study in this article.The application density of SFCM ranges from 1.20 g/cm³ to 1.70g/cm³ and solidified speacer ranges from 1.30 g/cm³ to 2.00g/cm³.Besides,solidified speacer is not used to support casing or isolate formation,it can return to the surface or stay in well as an additional part according to requirement of returned position of cement slurry,thus to avoid the defect of MTC.