一种大温差弹韧性水泥浆

长封固段大温差气井固井面临水泥浆顶部易超缓凝，水泥环易发生密封失效致环空带压等问题。通过研选抗高温大温差缓凝剂和降失水剂，可满足170℃以低100℃温差水泥石强度发展要求；优选抗高温弹韧性材料，降低水泥石脆性，增强水泥石弹韧性。研制出大温差弹韧性水泥浆体系，密度在1.50~2.20 g/cm3范围内可调，水泥浆流变性好，API失水量小于50 mL；50℃温差下密度为1.50 g/cm3低密度水泥石72 h抗压强度可至11.5 MPa，60℃温差下密度为2.20 g/cm3水泥石72 h抗压强度可至15.3 MPa，70℃温差下密度为1.88 g/cm3水泥石抗压强度达17.7 MPa，且水泥石弹性模量均小于7 GPa，抗折强度大于3.5 MPa；水泥环密封完整性评价显示，水泥环可满足90 MPa压力30轮次加卸载密封要求。该大温差弹韧性水泥浆体系在西北油田分公司顺北4井φ193.7 mm+φ206.4 mm尾管回接固井中成功应用，一次封固段长5693 m，上下温差约105℃，固井质量优质，为其他超长封固段气井固井提供成功范例。 

Study and Application of a Large Temperature Difference Cement Slurry with Good Elasticity and Toughness

Cementing of a gas well with long section to be cemented and big temperature difference has been challenged with difficulties such as ultra-long time of retarding of the top cement column and retained pressure in annular space resulted from failure of cement sheath. Studies have been conducted on the selection of retarding agents and filter loss reducers that can satisfy the requirements of cementing at 170 ℃ with temperature difference of about 100 ℃ and the strength development of set cement. High temperature additives with good toughness were also selected and used in laboratory studies to reduce the brittleness and to enhance the elasticity and toughness of the set cement. Using these selected additives a large temperature difference cement slurry with good elasticity and toughness was developed. The cement slurry had densities adjustable between 1.50 g/cm3 and 2.20 g/cm3, good rheology, API fluid loss of less than 50 mL, 72 h compressive strength of 11.5 MPa of a 1.50 g/cm3 low density set cement at temperature difference of 50 ℃, 72 h compressive strength of 17.7 MPa of a 1.88 g/cm3 set cement at temperature difference of 70 ℃, and the set cement had elastic modulus of less than 7 GPa and flexural strength greater than 3.5 MPa. Inspection of the integrity of the cement sheath showed that the cement sheath was able to undergo 30 turns of loading and offloading of 90 MPa. This cement slurry was successfully used in the tieback of φ193.7 mm and φ206.4 mm liners in the well Shunbei-4 drilled by the Northwest Oilfield Division of Sinopec, with 5693 m open hole cemented with high quality in one try. The difference of the temperatures between the bottom and top was 105 ℃. The cementing operation of the well Shunbei-4 has set up an example of successfully cementing long section of a gas well