用水泥浆封固井壁实施近平衡钻井

CARRYING OUT NEAR-BALANCED DRILLING BY ISOLATING BOREWALL USING CEMENT SLURRY

在钻进过程中 ,为了保证井下安全 ,实施近平衡钻井 ,人们往往采用技术套管来封固流砂层、易垮塌层、水层及多个压力层系的井段。但这样做的不足之处是 :在未下技套之前遇到复杂井段不易对付 ;下技套耗资较大 ;受井身结构的限制或探井未知因素的影响 ,往往仍有一些复杂地层技套没有封掉 ,从而影响到正常钻进。江苏油田在实践中摸索了用水泥浆封固复杂井段 ,从而实现安全钻进的目的。即在钻过复杂井段后 ,注入一定量的水泥浆 ,关井憋压 ,使水泥浆渗入地层 ,胶结了流砂砾石 ,堵住了水层 ,增加了井壁的稳定性。在闵 2 0 - 13井及墩 1- 3井 ,应用挤水泥的方法封固了上部的流砂层、砾石层、下部的易坍塌层 ,使打开目的层的钻井液密度由过去的 1.15g/cm3 和 1.16g/cm3 分别下降至 1.0 5g/cm3 和 1.0 8g/cm3 ,有效产油量增加。另外 ,上部井壁的稳定对于下一步采用乳化柴油进行近平衡钻井打下了基础。

Near balanced drilling technology is carried out to ensure the downhole safety during drilling, and intermediate casing is used for isolating the sand drifting zone, caving shale formation, water layer and multiple pressure intervals. However, there are limitations and disadvantages, e.g., the complicated intervals drilled before setting the intermediate casing are difficult to deal with; high cost of setting the intermediate casing; inefficient isolating of some intervals due to the limitations of the casing programs and the unknown factors when drilling the exploration wells, which in turn affects drilling operation. In Jiangsu Oilfield, a method is found in practice of isolating the complicated intervals using cement slurry, thus carrying out safe drilling. This method is described in the paper, i.e., after penetrating the complicated interval, a certain volume of cement slurry is pumped down and then raise the pressure by closing the well, causing the cement slurry entering into the bore wall, consolidating the drifting sand and gravel and plugging the water layer. The method can increase the well stability extremely. In wells Min20 13 and Dun1 3, by using this method of cement squeezing, the upper sand drifting layer and gravel layer, as well as the lower sloughing layer were effectively isolated, and the densities of drilling in fluid were reduced from 1.15-1.16g/cm 3 to 1.05-1.08g/cm 3, and the production rate was also effectively increased. In addition, the borehole stability in upper section is very important for realizing the near balanced drilling using the emulsified diesel oil.