摘要
随着地层埋深增加,岩石脆性降低,逐渐由硬脆性转变为韧性,而常规矿物组分法评价泥页岩脆性时没有考虑地层应力(埋深)的影响,因此评价结果存在一定误差。为此,从岩石脆性的最初定义出发,在不同围压条件下对陆相泥页岩岩样进行了力学测试,并利用应变法分析了泥页岩的脆性特征。结果表明:随着围压升高,泥页岩的弹性应变与塑性应变均增大,而脆性指数降低;泥页岩的弹性应变与塑性应变具有非常好的正相关性。对于文中所研究区块,埋深1 250.00,2 500.00和3 500.00 m处及埋深3 500.00~5 000.00 m和5 000.00~6 000.00m范围内的泥页岩脆性指数分别约降低5.97%,8.55%,10.74%,14.00%和18.00%;当泥页岩储层中脆性矿物含量分别大于65%,60%,55%和小于50%时,其开发埋深下限分别为6 000.00,5 000.00和3 000.00m以及基本不具备商业开发价值。研究结果表明,将应力(埋深)对泥页岩脆性的影响定量化,可以对采用矿物组分法计算的泥页岩脆性指数进行校正,为优选可压裂层段提供依据。
As well depth increases, formation rocks brittleness may be reduced and consequently manilest as ductile behavior. Conventional mineral composition can be usect to assess the brittleness ofshales. Because it does not take the impact of confining pressures (burial depths) into account, one arrives at less than satisfactory assessment conclusions. Under such circumstances, mechanical tests were conducted with continental deposit shale samples under different confining pressures and a strain method was deployed in a tested result analysis to highlight brittleness features of the shale. Research results showed that both elastic and plastic strains may increase with confining pressures while the brittleness index may decrease. Within the concerned Block,the brittleness index of shale at the depths of 1 250. 00 m,2 500. 00 m,3 500. 00 m and between the interval of 3 500. 00-5 000.00 m and 5 000.00-6 000. 00 m fell approximately 5.97%, 8. 55%, 10. 74%, 14. 00% and 18.00%, respectively. With brittle minerals content in these shale reservoir formations over 65 %, 60G, 55% and below 50%, the formation depth limitation for economic development of those reservoirs are determined to be 6 000. 00 m,5 000. 00 m^2 500.00 m and no commercial value,respectively. So the shale brittleness index determined from conventional mineral composition can be calibrated through quantification of impacts of stresses (burial depths) and it can provide help in the identification of intervals for staged hydraulic fracturing.
出处
《石油钻探技术》
CAS
CSCD
北大核心
2017年第3期113-120,共8页
Petroleum Drilling Techniques
基金
国家科技重大专项"盘县-金沙地区海陆交互相页岩气勘查评价应用试验"(编号:2016ZX05034004-007)部分研究内容
关键词
地层应力
埋深
泥页岩
脆性指数
岩石力学试验
应变
confining pressure
burial depth
shale
brittleness index
rock mechanical test
strain