宁东油田致密油储层损害机理与对策

Damage Mechanism and Countermeasures for Tight Oil Reservoirs in Ningdong Oilfield

  • 摘要: 鄂尔多斯盆地宁东油田致密油储层岩性复杂、低孔低渗、非均质性强,钻井过程中钻井液漏失情况多发,固相、液相侵入极易造成储层损害。为明确宁东油田致密油储层的微观特征与损害机理,降低钻完井对储层的损害,进行了SEM扫描、固液伤害性测试等试验研究,证实该油田致密油储层损害的主要原因为固相侵入、水锁及伴有的水敏感性和盐敏感性;明晰了该油田致密油储层的损害机理,发现钻井所用钾铵基聚合物钻井液对致密油储层的损害较大,采用隐形酸对储层进行处理时渗透率恢复率较低。针对该油田致密油储层损害机理和钻井所用钻井液的缺点,构建了低损害无固相钻井液,其黏度为45.5 mPa·s,API滤失量为3.5 mL,对储层损害较低,渗透率恢复率达85%以上,可满足宁东致密油储层保护需求。研究结果为鄂尔多斯盆地致密油储层保护技术措施的制定提供了依据。

     

    Abstract: Tight oil reservoirs in Ningdong Oilfield in Ordos Basin are characterized by complex lithology, low porosity and permeability, and strong heterogeneity. Drilling fluid losses occur frequently during the drilling process, and the invasion of the solid and liquid phase can easily cause damage to the formation. In order to determine the microscopic characteristics and damage mechanism of the tight oil reservoir in Ningdong Oilfield and reduce the damage to the reservoir during drilling and completion, systematic experimental studies such as scanning electron microscope (SEM) and solid-liquid damage tests were carried out. It was determined that the main causes of damage to the studied tight oil formation were solid phase invasion, water blockage, and associated water and salt sensitivity. The damage mechanism of the tight oil reservoir in this oilfield was clarified. In addition, it was found that the potassium ammonium-based polymer drilling fluid caused great damage to the tight oil formation, and the permeability recovery was low when the reservoir was treated with invisible acid. In view of the damage mechanism of tight oil reservoirs and the shortcomings of drilling fluid used in the oilfield, a low-damage and solid-free drilling fluid was constructed with a viscosity of 45.5 mPa·s, an API filtration loss of 3.5 mL, achieving a permeability recovery more than 85%, which caused low damage to the formation and could meet the requirements of protecting tight oil reservoirs in Ningdong Oilfield. The research results can provide a basis for formulating technical protection measures for tight oil reservoirs in Ordos Basin.

     

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