油套同注工艺在降低管柱沿程摩阻中的应用

APPLICATION OF TUBING AND CASING INJECTION TECNOLOGY IN REDUCING PIPE STRING FRICTION

大型加砂压裂是开采非常规气藏的核心技术之一,该技术要求将携砂液大排量地挤入地层,从而沟通天然裂缝,形成复杂的网络裂缝系统。但随着排量的增加,压裂液的管柱沿程摩阻将极大地上升,给开采该类非常规气藏带来了极大的挑战。实践表明,油套同注工艺能够有效地降低大型压裂管柱沿程摩阻。采用降阻比公式计算管柱沿程摩阻,并结合流体力学计算管柱清水摩阻,借助当量直径计算不规则断面环空的清水摩阻。以川西实际施工摩阻数据为基础,修正了降阻比公式中的系数,得到一套针对川西油套同注工艺管柱摩阻计算公式。同时以川西×井实际施工数据为基础,计算了整个加砂压裂过程中油套同注工艺的管柱沿程摩阻值,描述了摩阻值随施工排量和砂浓度的动态变化过程,相比同排量下的油管注入,油套同注工艺可降低管柱沿程摩阻55 MPa左右。

Massive sand fracturing is one of the main technology to exploit unconventional gas reservoir which needs high delivery rate to squeeze the sand fluid into formation to communicate the natural fractures and create complex network fracture system. However,with the increase of delivery rate,pipe string friction of fracturing fluid will greatly rise which brings a great challenge to explore such unconventional gas reservoirs. Practice showed that the tubing and casing injection technology could effectively reduce pipe string friction of the massive sand fracturing. Drag ratio formula was used to calculate pipe string friction. Meanwhile,with the help of fluid mechanics and equivalent diameter,the water pipe string friction of tubing and casing was derived. Based on the actual friction data in western Sichuan,the coefficients in drag ratio formula were revised,then a formula to calculate the tubing and casing injection pipe stringfriction in western Sichuan was acquired. And using the fracturing data of XX well in western Sichuan,the tubing and casing injection pipe string friction was calculated in the whole process of sand fracturing,the dynamic change of pipe string friction with the delivery rate and sand concentration was vividly described. Compared with the tubing injection at the same delivery rate,the tubing and casing injection technology could reduce the pipe string friction around 55 MPa.