Study & Application Of High Inhibitive Perforating Fluid For Formation Damage Control

There are large areas of water-sensitive formations facing severe reservoir damage problems in Wangzhuang, Jinjia and Shanjiasi oil district of Shengli Oil Field. The application of ordinary water-based drilling fluid is limited to carry through perforating because of its inevitable disadvantages, such as high formation damage and cost waste. It can't protect formation well. According to geological analysis of Wangzhuang, Jinjia and Shanjiasi oil district, a new kind of high inhibitive water-based drilling fluid with good environment acceptability and reservoir protection effect has been developed.First, the reservoir damage mechanism of water-sensitive formations in Shengli Oil Field has been studyed. It is mainly because the hydration&swelling of large amounts of water-sensitive clay minerals, especially montmorillonite, and dispersion&migragation of kaolinite, that caused the reduction of reservoir permeability. So the inhibition effect of the drilling fluid must be enhanced as high as possible. By doing a lot of inhibition and compatible experiments, main component chemicals have been selected, such as positive shale stabilizer CETA, zwitterion polymer FA367, polyalcohols and organic positive colloid BPS. Finally, the formulation of this system has been optimized as below: 4% Bentonite base mud+ 0.3% CETA+ 0.2% XC+ 3.5% mixed anti-sloughing agent+ 0.15% FA367+ 0.3% mixed fluid loss additives+ 2% BPS+ 2% Polyalcohols.The evaluation results show that this new system performs many excellent properties. It has super high inhibit and anti-sloughing property, nice reological properties, fine temperature stability, low filer loss, resisting the temperature of 120℃, high permeability recovery rate, favorable lubrication property and low toxicity toenvironment.The key points of have been got as follow, first, a kind of new-style cationic inhibitor is applied to decrease ion exchange on reservoir surface. Second, temporary plugging agent is applied to decrease filter loss of perforating fluid .Third, appropriate surfactants are applied to decrease the surface tension of perforating fluid, and reduce the damage of reservoir.Till now, this drilling fluid system has been put into use in more than 5 wells in Binnan Oil Plant. The field application effects have shown that this system is helpful to keep the well wall stable, enhance mechanical drilling speed and drilling efficiency, and protect the oil reservoir effectively. Meanwhile, this system can largely reduce drilling cost compared with OBM. Considerable economic benefits have been gained for using this new system.