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.

本研究聚焦于从伊莫页岩（Imo Shale）与阿梅基组（Ameki Formation）地质单元中采集的膨润土的矿物学与化学性质，并与商业进口膨润土（CIC）开展对比，以评估其用于配制钻井泥浆（drilling mud）的适用性。本次研究共对约50块疑似膨润土黏土开展系统调研，筛选过程中对原料的pH值、电导率、化学组成、粒度、蚀变程度及过滤条件等参数进行了表征分析。将CIC与4块符合美国石油学会（API）钻井泥浆规范的样品，进行X射线衍射（X-ray diffraction, XRD）与X射线荧光（X-ray fluorescence, XRF）测试分析。高岭石型样品的矿物组成为：55%高岭石、20%石英、15%钾长石及10%赤铁矿；蒙皂石型样品的组分范围为：28%~47%高岭石、26%~32%石英、12%~20%绿脱石。商业进口膨润土（CIC）的矿物组成为：12%石英、10%钾长石、12%方解石、41%绿脱石及25%非晶质物质。SPL15以高岭石为主要矿物相，而SPL6、SPL8与SPL11（含CIC）均属于蒙皂石型且含有大量高岭石，唯CIC除外。XRF分析结果显示，所有测试样品的Al₂O₃含量为15.77%~25.49%（质量分数），Fe₂O₃含量为6.61%~10.01%，SiO₂含量为51.67%~59.11%，烧失量为7.57%~11.22%。通过XRD数据鉴定出蒙皂石族矿物中的绿脱石，部分样品中较高的铁元素浓度也佐证了这一矿物相的存在。CIC中可能含有更多的非晶态二氧化硅。部分黏土样品中还检测出坡缕石与碧玄岩。蒙皂石型样品具有较高的铁铝比，且富含钙基蒙皂石，这与商业进口膨润土（CIC）存在显著差异。基于上述测试结果，通过调控矿物学组成与化学组分以配制钻井液的核心技术指标具备实现可行性。将本地采集的黏土与加工后的CIC进行对比后发现，本地黏土存在显著的组分差异与不足。因此，需通过添加部分改性助剂对其进行提质处理，方能达到钻井泥浆配制所需的组分要求。