密闭取心饱和度校正数学模型

Correction Model of Oil and Water Saturation in Sealing Core

利用密闭取心井资料分析油、水饱和度是目前最直接有效的方法,但是由于岩心上提导致的孔隙体积变大、降压脱气和钻井液侵入等过程的影响,岩心测试油、水饱和度之和一般均只有75%～85%,油、水饱和度都有较大损失,因而需要对油、水饱和度进行校正,争取求准饱和度数据。本次研究进行了挥发过程及岩心上提过程的室内实验,发现密闭取心降压脱气过程是造成油水饱和度损失的主要因素,目前实验条件难以如实模拟这一过程,研究中以流体分流率原理为核心,建立了降压脱气的数学校正模型;降压还会导致孔隙增大,岩心的覆压孔渗实验能够准确反映这一变化,为油水饱和度校正提供依据。建立的密闭取心饱和度校正数学模型精度与保压密闭取心的测试结果相当,具有推广意义。钻井液浸入造成的油水饱和度损失数量比较小,但是疏松砂岩中强浸的岩心样品油水饱和度数据需要校正,校正量一般不大于2%。

It＇s the most directand effective method to analyze oil and water saturation by using sealed coring data. However, the total saturationof oil and water is only 75%- 85% due to the increasingpore volume caused by the processes of raising cores, degasification by release of pressure and mud invading. There are many losses in oil and water saturation during the process. Oil and water saturation should be corrected for exact data. This paper provides experiments of volatilization process and raising cores process. The process of degassing is the main factor that causes the loss of oil and water saturation. It＇s very difficult to simulate this process really. Based on the split-flow principle, the correction model of degassing caused by pressure drop is made. Pressure dropping can cause the abundant porosity of the core, as can be accurately tested in the overburden pressure experiment and can provide the basic for oil and water saturation correcting. The precision of this correction model is similar with the result of the sealed coring pressure. And the influence caused by mud invading should be considered in coring of unconsolidated sand. Oil and water saturation should be corrected for complete invading specimen and high invading specimen, and the result is less than 2%.