致密油藏超长水平井固井水泥石力学性能评价

Evaluation on the mechanical property of set cement of super long horizontal wells in tight oil reservoirs

准格尔盆地吉木萨尔致密油储层具有特低渗、层厚、砂泥岩薄互层发育等特点，采用超长水平井开发，必须对超长水平井段射孔及多级压裂才能实现商业化开采。超长水平井射孔及多级压裂对水泥石完整性会造成不可逆破坏、存在层间窜流 风险。因此，研制了韧性膨胀防窜水泥浆体系，并结合力学软件和室内实验，优化水泥浆的防窜性能和水泥石抗拉强度、抗压强度、弹性模量、泊松比等力学参数。结果表明：优化后的水泥浆体系具有较强的防窜性能，静胶凝值从0Pa上升至200Pa，时间为3.5min;水泥石膨胀率达1.4%,可较好解决微环空问题；水泥石抗压强度38.6 Mpa,抗拉强度4.25 Mpa,弹性模量3616.0 Mpa,泊松比0.37。与常规水泥石相比，优化后的水泥浆体系和水泥石性能既能够确保超长水平井的固井质量，同时又能满足压裂施工后水泥石完整性和封隔性要求。

Jimsar tight oil reservoirs in the Junggar Basin are characterized by extra low permeability, thick layer and developed thin interbed of mudstone and sandstone, and they are developed by using super long horizontal well. In order to realize its commercial exploitation, therefore, it is necessary to carry out perforating and multi-stage fracturing in super long horizontal sections. However, the perforating and multistage fracturing in super long horizontal wells leads to the irreversible damage to the integrity of set cement and results in the risk of interlayer channeling. To solve this problem, ductile expansion anti-channeling slurry system was developed in this paper. Then, the anti-channeling property of slurry and the mechanical parameters of set cement (e.g. tension strength, compression strength, elastic modulus and Poisson's ratio) were optimized by means of mechanical software and laboratory experiments. It is indicated that the optimized slurry system has stronger anti-channeling property with static gelling value rising from 0 Pa to 200 Pa within 3.5 min. The expansion ratio of set cement is 1.4%, so the micro annulus can be solved better. Tension strength, compression strength, elastic modulus and Poisson's ratio of set cement are 38.6 Mpa, 4.25 Mpa, 3 616.0 Mpa and 0.37, respectively. The optimized slurry system and set cement are superior to conventional set cement and they can not only ensure the cementing quality of super long horizontal wells, but also satisfy the requirements on integrity and isolation of set cement after the fracturing.