深层—超深层裂缝性致密砂岩气藏加砂压裂技术——以塔里木盆地大北、克深气藏为例

目前国内对于深层—超深层裂缝性致密砂岩气藏实施压裂改造的技术瓶颈主要是耐高温加重压裂液的性能和分层改造技术。为此,以塔里木盆地大北、克深气藏为例,在开展天然裂缝开启条件、垂向地应力和裂缝性砂岩暂堵转向等压前评价的基础上,研制了耐高温加重压裂液,研发了针对深井与超深井的常规加砂压裂技术以及以提高长井段储层纵向动用程度为目的的暂堵转向复合压裂技术,并进行了现场应用实验。结果表明:(1)在天然裂缝的激发阶段,应提高净压力,采用小粒径支撑剂降滤或暂堵等技术措施,改造天然裂缝且使其保持一定的导流能力;(2)在主裂缝的造缝阶段,应调整排量控制净压力,采用冻胶造缝的连续加砂模式,沟通天然裂缝;(3)压裂液选用KCl和NaNO_3无机盐加重,其中NaNO_3加重压裂液最高密度达1.35 g/cm~3,最高耐温180℃;(4)常规加砂压裂技术应用在天然裂缝发育一般或不发育的储层,压裂管柱以直径88.9 mm的油管为主,使用KCl或NaNO_3加重压裂液,压裂后的产气量比压裂前可提高2~5倍;(4)暂堵转向复合压裂技术应用在天然裂缝较发育的长井段储层,压裂管柱以直径114.3mm的油管为主,使用NaNO_3加重压裂液,压裂后的产气量比压裂前可提高1~3倍。结论认为,所形成的加砂压裂系列技术能够为塔里木盆地深层—超深层裂缝性致密砂岩气藏的高效开发提供技术支撑。

Sand fracturing technologies for deep and ultra-deep fractured tight sandstone gas reservoirs: A case study of Dabei and Keshen gas reservoirs in the Tarim Basin

The technical bottlenecks for the fracturing stimulation of deep and ultra-deep fractured tight sandstone gas reservoirs lie in the properties of high-temperature weighted fracturing fluid and the separated layer stimulation technologies. In this paper, Dabei and Keshen Gas reservoirs in the Tarim Basin were taken as examples. After prefrac evaluation was carried out from the aspects of natural fractures opening conditions, vertical in-situ stress and temporary plugging and diverting of fractured sandstone, high-temperature weighted fracturing was prepared and the conventional sand fracturing technology for deep and ultra deep wells and the temporary plugging and diversion fracturing technology to increase the vertical producing degree of reservoirs in long hole sections were developed and tested on site. And the following research results were obtained. First, during the activation of natural fractures, it is necessary to increase the net pressure and take the measures of small-size proppant filtration reduction or temporary plugging to stimulate natural fractures and keep their flow conductivity. Second, during the creation of main fractures, it is necessary to control the net pressure by adjusting the pumping rate and adopt the continuous sand mode of gel fracturing to make the natural fractures communicate. Third, inorganic salt KCl and NaNO3 are selected to weight the fracturing fluid. And the maximum density of NaNO3 weighted fluid is 1.35 g/cm3 and its highest temperature is 180 ℃. Fourth, the conventional sand fracturing technology is applied in the reservoirs with a few or undeveloped natural fractures. Its fracturing string is mainly the 88.9 mm tubing and KCl or NaNO3 weighted fracturing fluid is adopted. And the gas production rate after fracturing is 2 to 5 times higher than that before fracturing. Fifth, the temporary plugging and diversion fracturing technology is applied in the long hole sections where the natural fractures are developed. Its fracturing string is mainly the 114.3 mm tubing and NaNO3 weighted fracturing fluid is adopted. And the gas production rate after fracturing is 1 to 3 times higher than that before fracturing. In conclusion, this series of sand fracturing technologies provide a technical support for the efficient development of deep and ultra-deep fractured tight sandstone gas reservoirs in the Tarim Basin.