Well Cementing with Low Friction Pressure Resistant Leaking Preventive Low Density Cement Slurry

In the Sulige gas field in Changqing Oilfield, the Liujiagou formation is a low pressure formation, the low density cement slurries presently used in this area have poor pressure resistance; the cement slurries under high pressures will have their density increased and rheology deteriorated. In field operations with these cement slurries, the operation pressures were high, generally causing the cement slurries to be lost into the formations, and the cementing quality is poor because of less cement slurries in the annulus. To solve this problem, a new cement slurry with low friction low density was formulated. This new cement slurry is pressure resistant and has the property of preventing itself from being lost into formations. Using the close packing theory, particles of 4 sizes were selected. A light material with excellent pressure resistance and other appropriate additives were selected to formulate the target cement slurry. The density of the new cement slurry is adjustable between 1.25 g/cm³ and 1.35 g/cm³, the Fanning friction coefficient was reduced by about 50%. The new cement slurry has good pressure resistance and leaking preventive property. Study on the agitation and mixing techniques shows that mechanical agitation and mixing can be used, 99% of the properties of the bulk sample and those of the small sample coincide with each other, ensuring the qualification and efficiency of the cement mixing. In field operations in the Sulige gas field, four wells were cemented with success, no loss of cement slurry has ever happened, and the cementing job was qualified. During the cementing, the operational pressure was significantly reduced, and the job quality was obviously improved. This laboratory study and the field application provide a strong technical support to cementing wells penetrating low pressure formations into which cement slurries are easily lost.