低摩阻耐压防漏低密度水泥浆固井技术

长庆苏里格气田刘家沟组地层承压能力低，现有低密度水泥浆体系耐压性能差，受压后密度上升、流变性能差，施工压力高，易发生漏失，造成水泥浆返高不够、封固段固井质量差。为此设计研发了一种低摩阻耐压防漏低密度水泥浆体系，运用紧密堆积理论进行水泥浆四级颗粒级配，优选耐压性能优良的减轻材料，选用合适的外加剂形成低摩阻耐压防漏低密度水泥浆配方。水泥浆密度为1.25～1.35 g/cm3，范宁摩阻系数降低约50%；耐压性能良好，防漏效果明显，综合性能优良。开展混拌工艺研究，采用纯机械混拌工艺，混拌大样与小样性能吻合率达到99%，保证了混灰质量和效率。在苏里格气田试验应用4口井，固井施工正常，未发生漏失，固井质量合格；施工压力明显降低，固井质量显著提升，为低压易漏地层固井提供有力的技术支撑。 

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.