高渗透地层压裂液滤失模型研究

RESEARCH ON LEAKOFF MODEL OF FRACTURE FLUID FOR HIGH-PERMEABILITY RESERVOIR

对于高渗透地层而言,由于压裂液滤失速度较快,滤失量较大,难以形成严格意义上的滤饼区,这时压裂液的滤失主要是受裂缝与油藏之间压力差的作用,而传统的滤失模型将裂缝到油气藏的区域分为滤饼区、侵入区和油气藏区,考虑压裂液的滤失受到压裂液黏度、地层流体压缩性和压裂液造壁性等3个因素的共同作用,但不能描述压裂液向地层作动态渗流的情况,因此,就无法用于高渗透地层压裂液的滤失计算。文章考虑压裂液为非牛顿型流体、在施工过程中向地层作平面二维流动的实际情况,利用数值模拟方法,建立了高渗透地层压裂液滤失模型,通过数值求解,验证了模型的可靠性。计算结果表明:对于高渗透地层,考虑地层未有滤饼区的形成、压裂液的非牛顿特性和压裂液向地层作二维渗流滤失的实际情况,计算结果更符合现场实际,这可以减少压裂施工的风险,提高压裂设计的准确性。

The fluid leakoff is rapid and substantial in formation with high permeability and it's difficult to form rigorous filter cake. In this case, the leakoff is mainly affected by the pressure differential between fracture and reservoir. The traditional leakoff model is invalid as it divides fracture to reservoir area into filter cake zone, invasion zone and pool zone and assumes leakoff is affected by fracture liquid viscosity, liquid compression, and plastering ability. The traditional model fails to describe fracture fluid dynamic percolation to formation and is unfit for leakoff calculation for high-permeability formation. In this paper, a novel leakoff model is established according to the actual condition of 2D flow and treating the fracture fluid as non-Newton fluid, it is further proven to be reliable by the numerically resolving. Just as the calculated results suggested, filter cake is not present in high-permeability reservoir and the 2D flow of non-Newton fracture fluid to formation is much consistent with the field case. Therefore, the introduction of this model can decrease the operation risk and improve the veracity of fracture design.