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和阿美基地层中恢复的膨润土的矿物学及化学性质，并与商业进口膨润土（CIC）进行对比，评估其在钻井泥浆配制中的适用性。针对约50种疑似膨润土粘土进行了研究，并在筛选过程中利用了起始材料如pH值、电导率、组成、粒度、风化程度及过滤条件等性质。CIC及符合API钻井泥浆标准的四个样品均进行了X射线衍射（XRD）和X射线荧光（XRF）分析。高岭石型膨润土由55%高岭石、20%石英、15%钾长石和10%赤铁矿组成。滑石型膨润土的组成范围从28%-47%高岭石、26%-32%石英、12%-20%非晶石。CIC由12%石英、10%钾长石、12%方解石、41%非晶石和25%非晶质材料组成。SPL15主要成分为高岭石，而SPL6、SPL8和SPL11，包括CIC，均为滑石型，含有大量高岭石，但CIC除外。XRF分析结果显示，其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%，以及灼失量为7.57%-11.22 wt%。从XRD数据中识别出滑石族矿物非晶石，其某些样品中Fe浓度较高。CIC中可能存在更多的无定形相硅。在部分粘土中还存在埃洛石和玄武岩。滑石型膨润土具有较高的Fe/Al比率，富含钙滑石，与CIC存在显著差异。基于这些结果，利用矿物学和化学组成制定钻井液配方的首要标准是可行的。与处理后的CIC进行比较，发现当地粘土在组成上存在显著的不一致或缺乏。因此，可能需要添加某些添加剂以实现预期的组成。