柴北缘中侏罗统湖相泥页岩储层矿物组成与脆性特征

Mineral Compositions and Brittleness of the Middle Jurassic Iacustrine Shale Reservoirin Northern Qaidam Basin

运用X射线衍射技术,对柴北缘中侏罗统46块岩心泥页岩样品和15块露头泥页岩样品进行了定性和定量分析。结果表明研究区泥页岩矿物成分中黏土矿物含量最高,介于33%-79.7%之间,平均54.3%;其次为石英,含量介于14.5%-57.8%之间,平均35.4%;碳酸盐矿物含量较少,总量一般介于0-13%之间,个别样品大于15%,露头样品与岩心样品矿物成分有差别。黏土矿物组合特征反映出研究区进入中成岩阶段,对应有机质演化的成熟阶段,具有适宜页岩油气形成的成熟度条件。扫描电镜显示,研究区泥页岩发育3种孔隙类型。与海相页岩相比,柴北缘中侏罗统泥页岩黏土矿物含量高但敏感性矿物含量低,石英、长石等脆性矿物含量偏低但达到湖相泥页岩开发标准,脆性指数平均为42.6%,整体上具有较好的脆性和可压性,有利于该区湖相页岩的压裂改造。

X-ray diffraction（XRD） was used to qualitatively and quantitatively analyze Middle Jurassic lacustrine shale samples fromthe northern Qaidam Basin. Results revealed that clay minerals were dominant with a range of 33% -79.7% and averaged in 54.3%.Quartz mineral ranged from 14.5% to 57.8% with an average of 35.4%. Carbonate mineral ranged from 0 to 15%. Clay mineralcompositions show a middle diagenetic stage, corresponding to a mature evolutionary stage of hydrocarbons with a suitable maturitycondition for shale oil and gas formation. Three types of pores were found in the study area including intragranular pore, intergranularpore, and marco fracture. Compared with marine shales, Middle Jurassic lacustrine shales in the northern Qaidam Basin have highercontent of clay minerals, less sensitive mineral, and relatively lower content of brittle minerals such as quartz and feldspar but can meetcriteria for the lacustrine shale gas reservoir exploitation. The average index of mineral brittleness was 42.6% suggesting a good property of brittleness and compressibility which is good for fracturing.