Hematite In Oil Drilling Applications
One of the most ubiquitous ores of iron is hematite and it finds uses well beyond the blast furnace: as an essential component in some modern drilling fluids for oil and gas drilling. The exploration industry highly values hematite for its performance characteristics, high purity and low cost. Hematite is available from African Pegmatite, milled to exacting specifications for ready to go applications.
Hematite is a mineral used in the oil extraction industry as a component in drilling fluids. Drilling fluids are oftentimes water- or oil-based and the addition of hematite - which like manganese oxides and barite - contribute to an increasing density in the fluid.
This is particularly useful as the primary functions of drilling fluid are to maintain hydrostatic pressure at the drill site (to prevent formation fluids entering the bore), to carry out drill cuttings and to keep the drill bit cool and relatively contaminant-free during the drilling process. Drilling fluids prevent blowouts. Furthermore, drilling fluids can be thought of as acting as lubricants for certain phases of the drilling process.
The most common drilling fluids across oil and gas extraction operations are oil based mud (OBM) and water based mud (WBM). In these ‘muds’, the largest component is bentonite clay, mixed with either oil or water, supplemented with any desired additives(1). Hematite is such an additive, and is described as a weighting agent. As their name suggests, weighting agents add weight (i.e. density) to the mud, meaning the drilling fluid will stay present at the drill head for a longer period - important considering how long certain drilling regimes are, particularly through the harder forms of rock. ‘Mud’ is a commonly used term to describe drilling fluids, owing to clays being the largest component in a large proportion of drilling fluids.
Drilling fluids are essential in petrochemical exploration as they enable efficient drilling to the target depths to reach the oil and/or gas deposit. Modern oil extraction would be almost impossible without drilling fluids(2). During drilling, five key factors are measured in the mud to ensure ongoing success: rheology, density, fluid loss, solids content and chemical properties. Hematite, as a weighting agent, is primarily concerned with density and solids content; as well as rheology.
Introduction To Weighting Agents
Weighting agents are added to the drilling fluid to allow the modulation and optimisation of a drilling fluid for a particular application, for example through certain hard rock types, or at extreme depths. They often are used to maintain density levels in the fluid, alleviating high formation pressures and ensuring a consistency in displacement of mud and other debris. As a general rule of thumb, the deeper the boring, the more weighting agent is required.
Barite and Manganese
Barite, from the Greek barus meaning ‘heavy’, is the most used additive in oil drilling as a weighting agent(3), and is a mineral consisting of barium sulfate. Owing to its high specific gravity of 3.9 to 4.4 g/cm3, it is a widely used weighing agent. The use of barite is not without its problems, however. Barite sag is a phenomenon whereby solids in suspension in the fluid fall out of the suspension and settle at high temperature and pressures(4), causing problems with ongoing drilling and an eventual stoppage of operations. Barite sag can be partially alleviated by the addition of ilmenite and other metal oxide ores. Furthermore, demand for barite is far exceeding production. It is thus imperative that alternative weighting materials are identified.
Manganese compounds, manganese(ii) and (ii) oxide, derived from hausmannite ore are also used widely as weighting agents. Because of its ability to form small, spherical particles, oxides of manganese represent the challenge of higher particle loss at high temperatures, which requires additional steps to negate(5).
Hematite (red iron oxide is an oxide and ore of iron, bearing the chemical formula Fe2O3, and a hardness of 5.5 to 6.5 on the Mohs scale. Its major use is as a source of iron for the production of that metal and of steel. Due to its hardness, high natural purity, abundance and low price, hematite has found increasing uses in fields removed from smelting, such as oil and gas production and exploration, as part of drilling fluids.
In comparison to barite, hematite enjoys advantages such as a higher specific gravity, a greater solubility in acidic media and an overall lower attrition rate - the latter due to its hardness. One of hematite’s headline claims as an improvement over barite, aside from it’s plentiful nature, is that it has a higher specific gravity of 4.9 to 5.3 g cm-3(6). Because of this, drilling companies can use less hematite in their mud solutions than barite, and achieve the same results. This results in a lower cost to weight the mud, and fewer solid particles dispersed through the mud. Hematite is additionally regarded as a good choice for drilling uses as it is incredibly pure and contaminant free as mined. Furthermore, better performance in terms of a reduced need for dilution, improved rate of penetration and a higher capacity for solids tolerance are other qualities associated with hematite as a weighting agent for drilling applications(7). Hematite’s major use as a drilling agent in oil exploration is in deep drilling(8).
As a general rule of thumb, the more hematite there is added to a water or oil based mud, the denser that mud will be. In some regions where drilling takes place, hematite has been found in the rocks themselves and has been shown that it acts as a ‘cement’ in deep subsurface gas reservoirs where the permeability of the naturally occurring cement is proportional to the amount of hematite it contains. The greater levels of hematite, the less permeable the cement, and therefore the better preservation over time of the resource - in this case natural gas(9). Magnetic susceptibility measurements were used to establish hematite presence. As part of the well bore directional surveying programme, magnetic measurements are taken. Such measurements are not affected by hematite (as magnetic shielding of the Earth’s magnetic field is not observed in pure hematite muds) but can be perturbed by magnetite(10). It is therefore crucial that the highest quality hematite be used - so as not to infer undue influence on vital measurements caused by errant magnetite. Magnetite is a common contaminant in some hematite sources.
Crucial to any drilling and extraction campaign is the stability of the well, including when using drilling fluids. Vertical homogeneity of the fluid is a strong indicator of whether the process will remain stable through sustained operation - with such homogeneity being relatively easy to achieve with hematite based muds. Uniformities through the vertical plane of hematite muds often achieve ca. 20% (lower values are preferred) with high compressive strength values in excess of 55 MPa(11).
Hematite In Oil Based Mud (OBM)
OBMs are characterised by having an oil-based continuous phase, with water in a dispersed phase alongside other additives such as emulsifiers and gellants.
Wetting is a concern for OBM drilling. Wetting is where water adheres to the solids in the mud, either the weighting agents or otherwise. Materials that are prone to wetting may cause excess water to reach the drilling area, which can result in clumping of the solids, leading to severe inefficiencies in the drilling process and potential degradation of the drill bit. In the most extreme cases, the clumping caused by wetting can render a drill site inoperable. Hematite is characterised as a low-wetting material, and thus the use of this over other weighting materials will ensure less wetting(12).
Hematite In Water Based Mud (WBM)
In WMB applications, lubricants are often used to ensure high efficiency drilling and to reduce friction and wear caused by solids including weighing agents such as hematite. It has been found that a 1% by volume addition of surfactant to the mud mixture was sufficient to reduce friction coefficients by 60% - increasing the longevity of the drill bit(13). In WBM scenarios, hematite can be used in quantities of up to 20% by weight, with a notable decrease in sedimentation relative to borite due to the high iron oxide content(14).
Hematite And Rheology
Rheology refers to the flow of matter, and particularly in the drilling space, the plastic flow of solids. This should not be confused with plastics as a material. Plastic flow is a movement proportional to an applied force, and specifically in petroleum exploration, a shape or phase change resulting from such a force. Rheological properties are profoundly affected by the presence of solid materials, and therefore adding hematite to a fluid will have an impact upon its rheological performance. Particle size is crucial (no more than 25 µm, but often far less)(15). Across multiple studies, hematite has produced higher density values, better gelling ability and higher plastic viscosity than barite(16), especially at deep boring depths. These qualities are continuous with successful long term depth drilling projects, affording stable bore holes.
Hematite, Drilling Fluids And The Environment
Oil drilling is not known as the most environmentally friendly activity. Hematite itself is non-toxic, yet care should be taken so as not to release too much drilling fluid, particularly in marine environments, particularly if it is of the OBM type. Barite is described as non-toxic only due to its insolubility in water. As with all industrial processes, reduction in the quantity of any material used is advantageous - drilling waste is the second largest waste stream originating from exploration(17). Hematite use instead of borite or manganese can aid in this due to the aforementioned higher density thus lower mass requirement.
Considerations When Using Hematite In Drilling Fluids
Hematite is a significantly harder material than barite. As such, hematite can itself cause wear on the drill bit and column under long term drilling situations, in addition to at high pressures. Research has shown that decreasing hematite particle size, and ensuring a narrow range of particle sizes, causes a positive effect on drilling bit erosion, i.e. less erosion over time, with comparable timeframes to barite(18). It has been proposed that hematite is only a sufficient replacement for barite if it is finely milled to a size of no more than 25 µm(19).
Because of the advantageous properties of hematite, barite and manganese, in some situations a combination of these materials are used as weighting materials. For example, a drilling operation may wish to take advantage of hematite’s longevity and hardness, barite’s wide inertness and manganese tetroxide’s oxidation properties(20) to provide a complimentary weighting phase in the mud suited to the local rock/sediment composition(21).
Life After Drilling: Future And Downstream Uses For Drilling Fluids Containing Hematite
Hematite based drilling fluids can be used in other methods beyond as drilling fluids. Their rheological properties, hardness and density make them appealing materials for a small selection of novel uses.
Staying within the drilling sector, research has shown that hematite drilling fluids can be used as a primary component in cement for the lining of drilling wells. This application relies on hematite’s hardness, the mud’s stability and the relative ease of forming it into a concrete type material. Patent literature shows that forming hematite rich drilling fluid into cementing walls for drilling wells is as easy as mixing the drilling fluid with a traditional cement material and a dispersant such as a styrene copolymer(22). Authors cite the highly suitable viscosity properties achieved, making in situ curing possible when a conduit is used. No comment was made on hematite containing drilling fluids and muds’ pozzolanic properties.
For sedimentation stability in directional wells, where hematite drilling fluid is used as a cement additive, it has been noted that the greatest levels of cement stability are when the material is produced at lower inclination angles due to increased particle sedimentation velocity(23). In essence, this means that while hematite in a cement for the lining of a well bore is an excellent choice, the curing of such a concrete will be less effective at higher angles - remedies such as higher pozzolanic material additives can be considered.
Although perhaps a niche area, hematite containing cement and concrete materials have been used as shielding barriers in high radiation areas(24). Many iron containing materials have long been used in radiation prevention applications. Addition of hematite to these concretes increased their unit density and therefore a smaller thickness needs to be used to afford the same level of protection.
- Hematite is fast becoming a popular choice as a weighting agent in drilling fluids for production applications in the oil and gas sector - offering high performance, good stability and broad applicability through different rock types
- Used in both oil- and water- based mud fluids, hematite provides enhanced rheological properties, and a higher specific gravity meaning less of it can be used relative to its competitors to achieve the same result
- Hematite is valued for being highly pure at the point of being mined and very hard, in addition to being economically attractive
- Other uses for hematite in the oil and gas sector include for stabilising the drill holes themselves and as shielding barriers
Hematite is a widely used ore of iron and finds wide uses in the oil and gas exploration and production sectors where it makes for an easier extraction. African Pegmatite is a preferred partner of the oil and gas sector, providing the highest quality hematite milled to precise specifications every time.
1 G. R. Gray et al., Drilling Fluid Components, in Composition and Properties of Drilling and Completion Fluids, 7th ed., Elsevier, Cambridge, MA, United States, 2017
2 J. M. Davies and P. F. Kingston, Sources of Environmental Disturbance associated with Offshore Oil and Gas Developments, North Sea Oil and Gas Resource - Environmental Impacts and Responses, Elsevier, London, 1992
3 M. E. McRae, Barite 2016 Materials Yearbook, United States Geological Survey, Washington DC, 2016
4 A. Mohamed et al., Sustainability, 2009, 11, 5617
5 A. M. Al Moajil et al., Evaluation of Dispersants for Drilling Fluids based on Manganese Tetraoxide, in: IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Tianjin, 2012
6 J. P. Rupert et al., The Effects of Weight Material Type and Mud Formation on Penetration Rate Using Invert Oil Systems, in: SPE Annual Technical Conference, San Antonio, TX, United States, 1981
7 J. Tovar et al., An Improved Hematite for Drilling Fluids, in: SPE Latin America and Caribbean Petroleum Engineering Conference, Caracas, 1999
8 S. D. Ukeles and B. Grinbaum, Drilling Fluids, in: Kirk-Othmer Encyclopedia of Chemical Technology, 5th ed., Wiley, Weinheim, Germany, 2000
9 K. Potter et al., Quantifying the Role of Hematite Cement in Controlling Permeability in a Deep Tight Gas Reservoir from the North Sea in: SPE Middle East Unconventional Gas Conference and Exhibition, Abu Dhabi, 2012
10 S. Ding et al., Partic. Sci. Tech., 2010, 28, 86
11 A. Ahmed et al., Sustainability, 2019, 11, 6776
12 J. T. Cline et al., Wettability Preferences of Minerals Used in Oil-Based Drilling Fluids, in: SPE International Symposium on Oilfield Chemistry, Houston, 1989
13 J. M. González et al., Colloids and Surfaces A: Physicochem. Eng. Asp., 2011, 391, 216
14 P. Ranjan and A. Dutta, Int. J. Dev. Res., 2017, 7, 16806
15 P. Xu et al., R. Soc. Open Sci., 2018, 5, 180358
16 P. O. Ogbeide and S. A. Igbinere, FUTOJNLS, 2016, 2, 68
17 S. I. Onwukwe and M. S. Nwakaudu, Int. J. Env. Sci. Dev., 2012, 3, 252
18 G. Quercia et al., Wear, 2009, 266, 1229
19 A. Tehrani et al., Alternative Drilling Fluid Weighting Agents: A Comprehensive Study on Ilmenite and Hematite, in: IADC/SPE Drilling Conference and Exhibition, Fort Worth, TX, United States, 2014
20 A. M Al Moajil et al., Removal of filter cake formed by manganese tetraoxide-based drilling fluids, in: SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, LA, United States, 2008
21 United States patent US6248698B1, 1999, expired
22 United States patent US4883125A, 1987, expired
23 S. S. T. Moradi and N. I. Nikolaev, Int. J. Eng. Trans. A, 2017, 30, 1105
24 O. Gencel et al., Mater. Sci., 2010, 16, 249