Study On Calculation Model Of The Cementing Strength Of Adhering Sand Casing

Because of the smooth surface normal casing, drill fluid is likely to adhere to theborehole wall in form of mud sheath, thus decreased the cementation strength of thecasing-cement and caused low cementing quality. As a technical measure to increase thecementation strength of cement sheath, the technology of adhering sand casing has beenwidely used in cementing operation in recent years. But comparing with normal casing, boththe force exerted on adhering sand casing and its medium of the interface of casing-cementare more complex, the traditional first interface cementation strength analytical method andindoor experiment are no longer suitable for adhering sand casing technology. Moreover,many scholars, both home and abroad, have concentrated on the pipe surface roughness thatcan increase contact area with cement sheath, but failed to see how it affect drill fluid’sfluidity. The author thought adhering sand caused some drilling fluids retain in sand andcannot be displaced, between sands a certain thickness stagnant layer formed as a result,which limited the improvement of cementing quality.The article analyzed the force on sand, cement sheath and cementing agent underdifferent damaging forms and did strength check, established the calculating model ofcementing strength of cement sheath of adhering sand casing, and analyzed the influence ofdifferent adhering sand factors, establish the evaluation technology of adhering sand casingcementing quality. On the basis of this, further consideration of sand block drilling flow,analysis of axial turbulent flow field of power law fluid in casing-annular space andcalculation of the displacement efficiency of cement paste of adhering sand casing had beenput into action, and then established the calculating model of cementing strength of adheringsand casing which take retention of drill fluid into consideration, finally verified the accuracyof theoretical model by the flat plate flow indoor experiments and field application. Throughthe study mentioned above, this article established the new calculating model of cementingstrength of cement sheath and sand particles of adhering sand casing and cementing qualityevaluation method, and pulled out a scheme which could increase cementation strength ofcement sheath of adhering sand casing effectively, thus truly reflect cementing quality ofadhering sand casing well.