淡水钻井液侵入对油层电阻率影响的理论分析和实验研究

淡水钻井液侵入油层通常出现减阻侵入现象，即冲洗带电阻率小于原状地层电阻率，但有时也存在相反的现象。对此现象进行理论分析，并且在实验室进行岩心模拟实验。理论分析和实验结果均表明：在淡水钻井液侵入条件下，当钻井液电阻率与原始地层水电阻率之比大于2．5时，油层出现增阻侵入和低阻环带现象，表现为冲洗带电阻率大于原状地层电阻率，且该比值越大，增阻侵入和低阻环带越明显；当钻井液电阻率与原始地层水电阻率比较接近时，油层表现出减阻侵入现象，即冲洗带电阻率小于原状地层电阻率，当侵入较深时，油层可能呈现出低电阻率特征。图3参8

Theoretical and experimental study of invasion influence of fresh drilling mud on oil pay resistivity

The invasion of fresh drilling mud usually results in low resistivity invasion profile of oil pays with higher deep detecting resistivity (R_(td)) than shallow resistivity (R_(ts)). However, R_(ts) may be higher than R_(td), which is theoretically analyzed and modeled from core experiment. Theoretical and experimental study suggests that high resistivity invasion profile occurs when the resistivity ratio of the drilling mud to initial formation water is higher than 2.5, and low resistivity invasion occurs when the two resistivities are close under the condition of fresh drilling mud invasion. The invasion of fresh drilling mud into oil pays is dependent on the height of oil column. After invasion of fresh drilling mud, oil pays with higher oil column show on log response a larger diversity between R_(td) and R_(ts).