Influence of MgO and CaCl<sub>2</sub> on the rheological properties of bentonitic clays from the new Paraíba-Brazil deposits using experimental planning and statistical analysis

Buriti, B. M. A. B.; Araújo, M. E. B.; Bastos, P. M.; Cartaxo, J. M.; Neves, G. A.; Ferreira, H. S.

doi:10.1590/0366-69132020663772771

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Articles • Cerâmica 66 (377) • Jan-Mar 2020 • https://doi.org/10.1590/0366-69132020663772771 copy

Influence of MgO and CaCl₂ on the rheological properties of bentonitic clays from the new Paraíba-Brazil deposits using experimental planning and statistical analysis

Influência do MgO e CaCl ₂ nas propriedades reológicas de argilas bentoníticas dos novos depósitos da Paraíba-Brasil utilizando planejamento experimental e análise estatística

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

New deposits of bentonite clays have been discovered in the Brazilian State of Paraíba; the most recent was at the municipality of Olivedos. Recent studies have discovered the presence of high levels of non-clay minerals that can produce unsatisfactory results when attempting to use these clays in drilling fluids. In order to make them suitable for this purpose, the MgO and CaCl₂ as chemical additives were used and their influences on the rheological properties of these clays were analyzed, using an experimental planning technique and statistical analysis. The samples were obtained using experimental modeling by the delineation of mixtures technique; first, the clays were transformed with sodium carbonate and then dosed with MgO and CaCl₂. The rheological properties, apparent viscosity (AV) and plastic viscosity (PV) were determined according to the Petrobras standard (AV≥15 cP; PV≥4 cP). The results showed that the values of AV and PV increased considerably and that MgO was the additive that contributed most to the improvement of these properties, making these additives suitable for use in water-based drilling fluids.

Keywords:
Olivedos’ bentonites; additives; drilling fluids

Table I Proportions of components (%) of simplex centroid network planning {3,2} with interior points added.

Composition	Clay (AM₁ or AM₂)	MgO	CaCl₂
1	100.00	0.00	0.00
2	97.50	2.50	0.00
3	97.50	0.00	2.50
4	98.75	1.25	0.00
5	98.75	0.00	1.25
6	97.50	1.25	1.25
7	99.16	0.42	0.42
8	97.91	1.67	0.42
9	97.91	0.42	1.67
10	98.34	0.83	0.83

Table II Rheological parameters of the compositions studied.

Composition	AV₁ (cP)	PV₁ (cP)	AV₂ (cP)	PV₂ (cP)
1	19.75	1.00	13.50	3.00
1	17.00	2.00	12.00	3.00
2	17.50	7.00	27.50	6.00
2	20.00	6.00	26.00	7.00
3	11.00	4.00	17.00	4.00
3	11.50	4.00	17.00	5.00
4	19.00	4.00	24.50	5.00
4	18.00	4.00	22.50	4.00
5	11.00	3.00	14.00	3.00
5	10.00	4.00	13.00	3.00
6	17.50	6.00	31.50	9.00
6	18.00	5.00	29.50	8.00
7	20.00	4.00	22.00	4.00
7	20.00	3.00	24.00	4.00
8	17.50	3.00	20.00	5.00
8	20.50	5.00	22.00	4.00
9	13.00	5.00	18.00	4.00
9	15.50	4.00	18.50	4.00
10	20.00	5.00	26.50	6.00
10	20.00	6.00	24.50	5.00
Specification EP-1EP-00011-A (19) API 13A: AV≥15cP; PV≥4cP

Table III Decoded regression equations for AV1, PV1, AV2, and PV2.

Variable	Equation
AV₁	AV₁=0.19.AM₁-0.04.B+138.91.C-1.46.AM₁.C+0.03.AM₁.B.C
PV₁	PV₁=0.02.AM₁+1.69.B+1.02.C
AV₂	AV₂=0.1.AM₂+134160.3.B+1.6.C-2039.0.AM₂.B-675.1.B.C+7.0.AM₂.B.(AM₂-B)
PV₂	PV₂=0.03.AM₂+1.33.B+0.53.C+1.54.B.C

Table IV Statistical parameters of the analyses of variance for the AV and PV variables relative to the selected models.

Variable	Model	Test F_cal	F_cal/F_tab	p-value	R²
AV₁	Special cubic	21.0972	6.8945	0.0000	0.8491
PV₁	Linear	16.7879	4.6762	0.0001	0.6639
AV₂	Complete cubic	35.3216	11.9330	0.0000	0.9266
PV₂	Quadratic	12.8902	3.9784	0.0002	0.7073

Table V Predicted and experimentally measured values for rheological parameters AV1 and PV1.

Composition	Component proportion (%)			Predicted value		Experimental value
Composition	AM₁	MgO	CaCl₂	AV₁ (cP)	PV₁ (cP)	AV₁ (cP)	PV₁ (cP)
i	97.70	2.10	0.20	19.18	5.73	19.12	6.35
ii	97.74	0.79	1.47	16.40	4.81	17.85	4.25
iii	99.52	0.28	0.20	18.16	2.69	18.83	3.79
iv	98.30	0.95	0.75	20.39	4.36	19.03	4.58

Table VI Compositions used for the model tests and the predicted and experimentally measured values for rheological parameters AV2 and PV2.

Composition	Component proportion (%)			Predicted value		Experimental value
Composition	AM₂	MgO	CaCl₂	AV₂ (cP)	PV₂ (cP)	AV₂ (cP)	PV₂ (cP)
i	98.73	0.95	0.32	24.92	4.57	25.50	5.00
ii	98.14	.95	0.91	23.79	5.74	23.50	5.00
iii	97.74	1.94	0.32	22.88	6.35	22.50	6.00
iv	97.70	0.36	1.94	20.84	5.22	21.50	5.50

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Influence of MgO and CaCl2 on the rheological properties of bentonitic clays from the new Paraíba-Brazil deposits using experimental planning and statistical analysis

Influência do MgO e CaCl 2 nas propriedades reológicas de argilas bentoníticas dos novos depósitos da Paraíba-Brasil utilizando planejamento experimental e análise estatística

Abstract

Influence of MgO and CaCl₂ on the rheological properties of bentonitic clays from the new Paraíba-Brazil deposits using experimental planning and statistical analysis

Influência do MgO e CaCl ₂ nas propriedades reológicas de argilas bentoníticas dos novos depósitos da Paraíba-Brasil utilizando planejamento experimental e análise estatística