大庆油田嫩二底标准层化石层引起套管损坏机理分析

Analysis of casing damage mechanism in fossil formation in N2 index bed of Daqing Oilfield

大庆油田套损严重,其中非油层部位套损井多数发生在油层顶部的嫩二底标准层.通过对套损层位岩心观测、多臂井径测井曲线与电测曲线比对、岩心X衍射全岩分析、岩石力学试验分析等,建立套损机理模型.力学分析表明化石层进水后,在流体压力以及地应力的作用下,剪应力超过化石层薄弱面抗剪强度后,地层失稳而发生成片套损.这一认识从根本上突破了以往嫩二底标准层油页岩遇水膨胀造成套损的观点.

Casing damage is very serious in Daqing Oilfield, for the casing damage wells with non-oil reservoirs, which usually takes place in the N2 index bed that is on the top of formation. By comparing the casing damage formation’s core analysis and multiple feeler caliper curve with electric curve and analyzing core’s X diffraction and rock mechanics testing results, casing damage’s model has been set up. Mechanics analysis shows that shear stress exceeds the weakness position of fossil formation’s crushing resistance due to the effect of both fluid pressure and earth stress after fossil formation has entered water. Large scale of casing damage will happen owing to formation’s instability. This point is a historical breakthrough to the mechanism of casing damage of N2 Index bed when shale swelling with water.