毫米级宽度裂缝封堵层优化设计

毫米级裂缝漏失一直是钻井堵漏的一大难题,封堵层的低承压问题不仅增大了堵漏材料的消耗量,而且还延长了钻井时间。为此,以封堵承压能力、累计漏失量、成封时间为指标,开展了2mm宽的裂缝封堵室内实验,评价了刚性颗粒、弹性粒子以及纤维3种封堵材料协同堵漏效果,并结合实验结果分析了不同材料协同封堵的机理。结果表明,刚性颗粒与弹性粒子组合形成的封堵层累计漏失量普遍大于400mL;弹性粒子与纤维材料组合形成的封堵层承压能力普遍小于6 MPa。3种材料协同组合封堵后承压能力提高到13 MPa,累计漏失量降为75mL。协同封堵过程中,刚性颗粒在裂缝狭窄处形成具有较高承压能力的骨架;弹性粒子在裂缝内发生弹性变形,弹性力作用于裂缝面并增强了裂缝面与封堵层之间的摩擦力,使封堵层更加稳定;纤维材料充填于颗粒之间并形成网络,增强了封堵层的致密性及整体强度。该成果为生产现场堵漏浆配方的优化提供了依据。

An optimal design for millimeter-wide fracture-plugged zones

Lost circulation in millimeter-wide fractures has all the time been a challenge to plugging in well drilling. The low pressure-bearing capacity of a plugged zone will result in excessive consumption of lost circulation materials (LCMs) and extra non-production time. In this paper, laboratory experiments were conducted on the plugging of two millimeter-wide fractures to evaluate the respective plugging effects of rigid particles, elastic particles and fibers. The maximum plugging pressure, total loss volume before sealing and plugging time were taken as the indicators of the LCM plugging effect. According to the experimental results, the mechanism of plugging of three LCMs synergy was also analyzed. Experimental results showed that the total loss volume of the plugged zone formed jointly by rigid and elastic particles was generally greater than 400 mL and the pressure-bearing capacity of the plugged zone formed by elastic particles and fibers was generally less than 6 MPa. As for the plugged zone formed by a combination of the three types of LCMs, the pressure-bearing capacity was increased to 13 MPa and the total loss volume was reduced to 75 mL. In the synergistic plugging process, rigid particles can form a frame with a high pressure-bearing capacity in the narrower parts of the fractures; elastic particles can generate the elastic force by elastic deformation to increase the friction between a fracture and a plugged zone and make the plugged zone more stable; fibers are filled in the pores of the particles to form a mesh to increase the tightness and strength of the plugged zone. The experimental results can be used for guidance to the optimal design of LCMs employed in the field.