龙马溪组页岩强度评价与分析

Evaluation and Analysis of Rock Strength for the Longmaxi Shale

准确全面地评价页岩储层的岩石强度,对页岩水平井井壁稳定性研究具有重要意义。针对龙马溪组页岩储层的特性,采用抗压法、屈曲硬度法和刻划测试法等多种评价方法,对其页岩抗压强度进行了综合评价与分析。评价表明,龙马溪组页岩的抗压强度大体为100～300MPa,平均为123.71MPa;与水接触后,页岩微裂缝附近的抗压强度可降低80%左右。研究表明,龙马溪组页岩的抗压强度受矿物组分相对富集的影响较大,石英含量高、黏土矿物含量低的区域抗压强度大;微裂隙对页岩整体强度具有决定性影响;在页岩水平井采用水基钻井液钻进时,必须加强对微裂隙的封堵能力,才能有效降低井壁失稳的风险。

In order to study the hole stability of horizontal wells in a shale formation,it is necessary to accurately and completely evaluate the rock strength in shale reservoirs.Based on the characteristics of shale reservoirs in the Longmaxi Formation,multiple evaluation methods（e.g.compression test,buckle hardness test and scratch test）were used to evaluate and analyze the compressive strength of shale.It is shown that the compressive strength of Longmaxi shale is generally in the range of 100-300 MPa,with an average of 123.71 MPa.After the shale has a contact with water,its compressive strength around the micro cracks fall by about 80%.Research showed that the compressive strength of Longmaxi shale was more influenced by the relative enrichment of mineral composition,the formations with high content of quartz and low content of clay mineral have higher compressive strength.The effect of micro cracks on strength of shale is a dominant characteristic.When water based drilling fluids are used for drilling horizontal wells in shale formation,it is necessary to strengthen the sealing capacity in micro cracks so as to effectively lower the risk of hole instability.