K^(+)敏感型VES转向解堵体系的研究与应用

Study and Application of a K^(+) Sensitive VES Diverting Block Removing Fluid

BZ油田储层层间渗透率级差大、非均质性强,解堵体系泵注过程中会优先进入高渗层,造成渗透率级差进一步增大,解堵效果不理想,且常规的VES转向体系只对二价阳离子敏感,在海上砂岩储层缺少二价阳离子的情况下应用效果不佳。针对该问题,以一种对K+敏感的黏弹性表面活性剂LD-VES为转向体系,与解堵体系配合使用形成了适用于海上砂岩储层的转向解堵体系。评价了转向体系的增黏性能、破胶性能、耐温性能、抗剪切性能以及与解堵体系的配伍性能,分析了转向体系的增黏机理以及破胶返排机理并进行了现场试验。结果表明,在KCl质量分数为7%时,增黏效果最佳,在温度为120℃、剪切速率为50 r/min下,体系黏度可以保持在1680 mPa·s^(-1),经过170 s高剪切速率剪切2 h后,黏度仍有1750 mPa·s^(-1),体系具有良好的增黏、耐温和抗剪切性能;转向体系与解堵体系混合后无沉淀、残渣生成,配伍性良好;加入相同体积煤油后,体系能够迅速破胶,具有优良的破胶性能。现场应用后日产液量27.92 m^(3)/d,较作业前的8 m^(3)/d提高3.49倍;日产油量16.75 m^(3)/d,达到作业前的4.05倍,具有显著效果。

Different pay zones in the BZ oilfield have big permeability differences among them and high heterogeneity, resulting in preferential flow of block removing fluids into zones with high permeabilities during pumping which in turn further increasing the permeability differences among different zones. This is quite unsatisfactory to the removal of the blockage existing in the reservoir formations. Furthermore, the conventional VES diverting fluids are only sensitive to divalent cations, and are thus behaving poorly in offshore sandstone reservoirs which lack divalent cations. To solve this problem, a viscoelastic surfactant LD-VES, a Ksensitive diverting fluid, were selected to combine with a block removing fluid to form a diverting block removing fluid for offshore sandstone reservoir operation. In laboratory experiment, the diverting fluid was evaluated for its viscosifying capacity, gel breaking performance, high temperature tolerance, shearing property and compatibility with the block removing fluid. The viscosifying, gel breaking and flowback mechanisms of the diverting fluid were analyzed. Field application of the diverting block removing fluid has shown that the fluid has the best viscosifying effect at KCl mass fraction of 7%. At 120 ℃, the viscosity of the fluid was 1, 680 mPa·s^(-1) at shearing rate of 50 r/min. After being sheared for 2 hours at 170 s, the viscosity was still 1,750 mPa·s^(-1), indicating that the fluid had excellent viscosifying capacity, high temperature tolerance and shearing property. The mixture of the diverting fluid and the block removing fluid produced no precipitation and residue, indicating that they had good compatibility with each other. After mixing kerosene with the diverting block removing fluid in 1 : 1 volume ratio, the gel of the diverting block removing fluid was soon broken. Field application of this diverting block removing fluid produced liquid of 27.92 m^(3)/d, a production rate 3.49 times higher than that before the application(which was only 8 m^(3)/d), and oil of 16.75 m^(3)/d, 4.05 times of the production rate before the application.