Comparative study of mineralogy and geochemical compositions of commercially imported bentonite and some locally derived bentonitic clays from Anambra Basin, Southeastern Nigeria

The study focused on the mineralogy and chemical properties of the bentonites recovered from the geological units of the Imo Shale and Ameki Formation, compared with commercially imported bentonite (CIC), for its suitability in the formulation of drilling mud. About 50 suspected bentonite clays were investigated, and properties of starting materials such as pH, conductivity, composition, grain size, degree of alteration, and filtration conditions were utilized during screening. The CIC and four samples that met the API specification for drilling mud were subjected to X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The kaolinite-type consists of 55 % kaolinite, 20 % quartz, 15 % K-feldspar, and 10 % hematite. The smectite-type range from 28-47 % kaolinite, 26-32 % quartz, 12-20 % nontronite. The CIC consists of 12 % quartz, 10 % K-feldspar, 12 % calcite, 41 % nontronite, and 25 % amorphous materials. The SPL15 is predominantly kaolinite, whereas SPL6, SPL8, and SPL11, including the CIC, are smectite-type with a significant amount of kaolinite, except the CIC. The XRF results, show Al2O3 (15.77-25.49) wt%, Fe2O3 (6.61-10.01) wt%, SiO2 (51.67-59.11) wt%, and loss on ignition (7.57-11.22) wt%. Nontronite, one of the smectite group of minerals, was identified from the XRD data. These were supported by elevated concentrations of Fe in some of the samples. More silica may be present in an amorphous phase in the CIC. Palygorskite and basanite are also present in some of the clays. The smectite-type contained an elevated Fe/Al ratio and is rich in Ca-smectite, which differs significantly from the CIC. Based on these results, the primary criteria for the formulation of drilling fluid, using mineralogy, and chemical compositions are achievable. A comparison with the processed CIC has revealed significant levels of compositional disparity/deficits in the local clay. Consequently, treatment/beneficiations with some additives may be necessary to achieve the desired compositions.

本研究针对从伊莫页岩（Imo Shale）和阿梅基组（Ameki Formation）地质单元中采集的膨润土开展矿物学与化学性质分析，并与商业进口膨润土（CIC）对比，以评估其用于配制钻井泥浆的适用性。本次研究共对约50份疑似膨润土黏土开展调研，筛选过程中检测了原料的pH值、电导率、组分、粒度、蚀变程度及过滤条件等参数。对商业进口膨润土及4份符合美国石油学会（API）钻井泥浆规范的样品开展X射线衍射（X-ray diffraction, XRD）与X射线荧光（X-ray fluorescence, XRF）分析。高岭石型样品的组成为55%高岭石、20%石英、15%钾长石（K-feldspar）及10%赤铁矿；蒙脱石型样品的组成为28%~47%高岭石、26%~32%石英、12%~20%绿脱石（nontronite）。商业进口膨润土组成为12%石英、10%钾长石、12%方解石、41%绿脱石及25%无定形物质。SPL15以高岭石为主，而SPL6、SPL8、SPL11及商业进口膨润土均属于蒙脱石型，且除商业进口膨润土外，其余三者均含有大量高岭石。X射线荧光分析结果显示，各样品的Al₂O₃含量为15.77~25.49 wt%，Fe₂O₃含量为6.61~10.01 wt%，SiO₂含量为51.67~59.11 wt%，烧失量为7.57~11.22 wt%。通过X射线衍射数据鉴定出了蒙脱石族矿物中的绿脱石，部分样品中较高的铁元素浓度进一步佐证了这一结果。商业进口膨润土中可能存在更多无定形二氧化硅。部分黏土中还检出了坡缕石（palygorskite）和碧玄岩（basanite）。蒙脱石型样品具有较高的铁铝比，且富钙蒙脱石（Ca-smectite），这与商业进口膨润土存在显著差异。基于上述结果，通过矿物学与化学组分分析实现钻井流体配制的核心标准是可行的。将本地黏土与商业进口膨润土对比后发现，本地黏土的组分存在显著差异与不足。因此，为达到理想的组分要求，可能需要通过添加部分改性剂对本地黏土进行处理或选矿提纯。