高含泥储层应力场变化对重复压裂的影响及对策

Influence and countermeasures of stress field change on refracturing in reservoir with high mud content

海拉尔油田BZ区块南屯组储层泥质含量高,岩石塑性强,重复压裂时由于应力场发生变化,尤其最小水平主应力的升高,导致水平方向近井裂缝复杂,为了提高该类储层压裂成功率,达到重复压裂增产目标,开展了高含泥储层应力场变化对重复压裂的影响分析,并进行了技术配套及现场试验。针对现场施工出现的停泵压力梯度升高、近井摩阻增大、低砂比砂堵的现象,确定其主要施工难点是近井微裂缝复杂、摩阻高、压裂液滤失大,结合低水平主应力差储层裂缝特点及封堵难点,研究了微裂缝封堵及降摩阻技术、微裂缝封堵后施工参数优化技术。该技术现场应用4口井,全部完成设计砂量,投产后初期单井日增油量为4. 1t,增油强度为0. 38t/(d·m)。该技术为由于应力场变化导致的重复压裂施工困难、无法实现增产目标的同类井改造提供了技术保障。

The BZ Block in Nantun formation reservoir of Hailar Oilfield has high mud content and strong rock plasticity,which leads to complex fractures near the wellbore in horizontal direction when making refracturing operation due to the change of stress field,especially the increase of the minimum horizontal principal stress.In order to improve the fracturing success rate of this kind of reservoir,and achieve the production increasing target of refracturing operation,the influence of stress field change on refracturing in reservoir with high mud content has been analyzed,and the technical matching and field test have also been carried out.In the fracturing process,some phenomena happened,such as rising pressure gradient when stopping the pump,increasing friction near the wellbore,and sand plugging occurring at low ratio of sand.It is determined that the main difficulties in the operation are resulted from the complex micro-fissure near the wellbore,high friction,and big loss of fracturing fluid.According to the fracture characteristics of reservoir with low difference of horizontal principal stress and difficulties in plugging,the technologies including micro-fissure plugging,friction lowering and operation parameters optimizing after the micro-fissure plugging have been studied,which have been applied to four wells in the fields.The designed sand loading volumes were all accomplished,and the initial average daily oil increment of single well was 4.1t with oil increasing intensity of 0.38t/(d·m).The technology has provided the technical guarantee for similar wells to overcome the difficulties that cannot achieve the oil production increasing target in the refracturing operation due to the change of stress field.