Evaluation Of Sealing Capacity Of Low Density Cementing Cement Ring

With the exploration and development of oil, facing the low pressure formation and weak formation more and more in the process of drilling, the lightweight cement slurry is accompanied by the treatment of these complex situations and develop and improve gradually. In the process of oil and gas field development, the sealing ability of cement sheath, which is to to adapt to the working condition, to prevent crossflow of formation fluid effectively in the late production and production process after cementation, has a direct relationship with Safety and exploitation of well.For the lightweight(1.2g/cm3) cement sheath of a domestic oilfield in working condition, can meet the requirements of the late exploitation and achieve effective sealing, this paper from the three factors:mechanics of the cement stone, volume contraction, poroperm characteristics, which can influence sealing of cement sheath and lead to crossflow of formation fluid, test those performance parameter, base on experiments and theory、 working contition and well construction, to establish the porosity-compression strength model and mechanical model, evaluate cement sheath whether formation stress fracture、 influence of volume contraction on the interfacial bonding quality and nfluence of poroperm characteristics on the macroeffect.According to the results of the experiment test and model evaluation,when subsurface pressure of middle of cement sheath more than90MPa, or bottom hole pressure more than70MPa, the cement sheath will be fail in tension. According to test for90days, research shows that temperature rise, the cement stone’volume contraction will be more obvious, and the trend tends to be stable with hydration. Cement stone’volume contraction reach a maximum value at90degrees for3.2%, it will formation microclearance at cementing interface. The permeability and porosity changes small after28days, porosity and strength have a nonlinear relationship. According to the model of evaluation, the lightweight cement stone is dense.The sealing ability evaluation of lightweight cement sheath, can guide the direction of the cement slurry material optimization. By adding the abiological fiber in cement slurry, the tensile strength increased, young’s modulus reduced and the mechanics of cement sheath has improved. By adding the sweller in cement slurry, volume contraction can be eliminated, and be an important significance to eliminate microclearance. Optimization of mechanics and volume contraction for lightweight cement sheath have an important realistic significance to later production and exploitation.