The Uses of The Al-Faidiyah Formation Oligocene-Miocene in The Drilling Mud Fluids (Bentonite) at Umm Ar Razam, North-East Libya

The lower member (Faidia Clay) of the Oligocene-Miocene Al Faidiyah Formation at Umm Ar Razam Quarry, northeast Libya has been investigated for its potential as a chemical additive (bentonite) in drilling oil wells. The thickness in outcrop of the examined clay unit is variable but information from the subsurface indicates a maximum thickness of about 25 m . Normally, these clay deposits have a dark green color that becomes brown when weathered. When wet, the clay forms a very plastic sticky mass with soap like textures. A number of mineralogical, chemical and physico-chemical laboratory analyses using X-ray diffraction (XRD), scanning electron microscopy (SEM-SE & SEM-BSE), X-ray fluorescence (XRF), ion exchange capacity (CEC) and surface area have been made in order to characterize the grade and quality of the examined clays. The overall results, shows that a montmorillonite represent the highest percentage (46 %), minor kaolinite (36 %) and trace chlorite (4 %). Other minerals of heterogeneous mixtures of non-clay minerals such as fine quartz grains, calcite, dolomite, gypsum, K-feldspar, ilmenite, anatase and hematite are also recognized. The presence of heterogeneous mixture of non-clay minerals reduce the rheological and physical properties as well as detract from the commercial performance of the Faidia clay. The unprocessed clay and clay after treatment with addition of up to 6 % of Na 2 CO 3 , did not achieve a swelling volume comparable with standard bentonite. The Faidia Limestone Member (the upper part of the Al Faidiyah Formation) is characterized by very high purity in Al Fatayah Quarry. It is extensively used for concrete aggregates, road tiles, blocks, paints, carpets, cement industry, papers, pharmaceuticals, water treatment, agriculture and plastics. The equivalent member in Umm Ar Razam Quarry has lower grade due to the presence of other carbonate (dolomite) and non-carbonates such as quartz, clay and glauconite minerals. Fossil contents and lithological nature indicate that this is a typical shelf environment.


Introduction
Clay and limestone raw materials of the Al Faidiyah Formation are economic interest. These raw materials were studied to gain a better understanding of other much larger and purer deposits, which are of economic importance. A series of earlier studies have been carried out from many workers on the Faidia Clay Member from the Umm Ar Razam area because of its economic potential (El Ebaidi, 1999;Lat and Zamarsky, 1992;Waston and Arhuma, 1992;El Ebaidi and Bakar, 1991;Sassi, 1991;Alami and Salem, 1981;and PRC, 1987). The descriptions, identification and analyses of clay minerals in this paper are based on the work of many authors (Moore and Renolds, 1997;Velde, 1992;Tucker, 1991Deer et al., 1992;Berner, 1971;Carrol, 1970;and Grim, 1968). The suitability of the clay raw material as a component in oil drilling mud fluid was also investigated. Evaluation of the clay need included laboratory tests of mineralogical, geochemical, physical and petrographical rock types for oil industry potential end use. The study area is poor in mineral resources, due to the absence of magmatic rocks. The Al Faidiyah Formation contains mainly limestone and clay deposits, no ore mineralization was found during this study. Iron ore (hematite) is rarely occurred in the Faidia Clay Member of the Al Faidiyah Formation. Faidia Limestone Member is extensively used for various applications such as aggregates in construction with specified size ranges, depending in the end use, road tiles, blocks, paints, carpets, lime production, cement industry, paper, pharmaceutical, water treatment, agriculture and plastics. Suitable limestone and clay deposits in Al Faidiyah Formation are available in sufficient quality, thickness and accessibility and also close to good transportation and to the market (clay in Umm Ar Razam and limestone in Al Fatayah Cement Quarries). A number of mineralogical, geochemical and physical laboratory assessments have been used to identified the grade and quality of the Al Faidiyah Formation in Umm Ar Razam and Al Fatayah quarries and to compare these clays with other commercial clays. This paper focusses on Faidia Clay Member from point of view of its application as a chemical additive (bentonite) in drilling oil wells for deep hole drilling, where high pressure and temperature occur. Smectite clays used for mud drilling fluids must meet the American Petroleum Institute (A.P.I.), or the Oil Companies Materials Association (O.C.M.A.) standards. Only certain natural Na and Naexchanged Ca smectites have the potential for meeting the A.P.I. and/or O.C.M.A. specifications.

Al Faidiyah Formation (Upper Oligocene-Lower Miocene)
The Al Faidiyah Formation is the youngest unit in the Umm Ar Razam area and stratigraphically ranges from the Upper Oligocene to Lower Miocene. The formation consists of limestone, whitish to yellowish, thick bedded to massive. It contains fossiliferous layers with dominant coralline algae. Pietersz (1968) introduced the name Faidia Formation, derived from the Qaryat (Qaryat in Arabic this means village) Al Faidiyah. It comprises of two members; the lower, Faidia Clay Member and an upper Faidia Limestone Member. The Al Faidiyah Formation have been studied at two different localities:

Al Faidiyah Formation (Al Fatayah Cement Quarry)
The Al Faidiyah Formation in this location consists mainly of limestone (Faidia Limestone Member), with green clay at the surface in the lower part of the formation. The limestone is mostly white, highly brightness (> 95 %) and according to Harries, 1979 is classified as a very high purity limestone (> 98.5 %), medium to fine grained, medium hard and contains corals of two genera Cyphastrea and Aleveopora (Figure 1), with abundant burrowing bivalves. It also contains encrusting red algae, echinoderm fragments with syntaxial overgrowth, molluscan shell fragments, large benthonic foraminifers (Nummulites sp. and Discocyclinids), bryozoans, gypsum crystals. It is dolomitized (1.7%) especially in the lower part, with micron sized euhedral dolomite replacing matrix.

Al Faidyah Formation (Umm Ar Razam Quarry)
This section of this quarry is located of about 3 km northeast Umm Ar Razam village, of about 45 km from Darnah City and 350 km from Benghazi City ( Figure 2

E-54
ISSN: 2413-5267 m thick, highly fractured and low grade where it consists of yellowish, medium hard limestone, with a packstone texture that contains glauconitic grains, benthonic foraminifers (Lepidocyclina), echinoderm fragments and common bryozoans. It is slightly dolomitized (up to 2% of the rock volume), some of the echinoid spines are replaced totally by micron sized clear dolomite crystals.

Fluid loss
The Umm Ar Razam clay has very high filtrate values compared to other standards (Table 1). The successive fluid loss of Umm Ar Razam clay will generate problem in oil drilling wells such as increasing the filter cake thickness leading to potentially stuck pipes, poor performance of electric logs, an unstable well borehole with possibility of caving, and total or partial loss of drilling mud fluids with chemicals into formations.

Mineralogical and Chemical Evaluations
A number of mineralogical identifications and chemical analyses have been done to characterize the Faidia Member using XRD, SEM, optical microscopy and XRF techniques.

X-ray Diffraction of Faidia Clay Minerals
Oriented mounts were produced on glass slides using Wilson's method (Wilson, 1987), clay fractions of < 2.0 µm to > 0.5 µm and < 0.5 µm were clay separation method been used. Clay samples were scanned from 2 -65 2Ɵ after untreated air drying, after glycol solvation and after heating to 350 and 550 °C for one hour ( Figure 5). The presence of these impurities in crude sample leads to poor rheological and binding properties of the Faidia clay.

Scanning Electron Microscopy
Scanning electron microscopy (SEM) has been used to provide additional useful information about the textural relationships between the smectite and associated minerals. Chemical analyses of clay minerals from the Faidia Clay Member were determined using SEM-EDX technique. The study of SEM also revealed other important petrographic features not apparent from the optical microscope, for example the identification of non-clay minerals (impurities) such as ilmenite, calcite, dolomite, anatase and orthoclase, quartz, gypsum and hematite (Figures 6, 7, and 8) and Table (

X -Ray Fluorescence (XRF)
A summary of geochemical analysis from X -ray fluorescence of the Faidia Clay Member in Umm Ar Razam quarry of the Faidiyah Formation is shown in Table (3).

Differential Scanning Calorimetry (DSC)
Samples of the Faidia Clay Member and other standards were run using DSC technique. The samples were heated continuously at regular rate from 25°C to 1200°C at 10°C/min. Curves for the various clay minerals obtained by DSC (Figure 9) are typically as expected for montmorillonite.

Estimation of organic matter + H 2 O content by loss on ignition (LOI)
A standard method with ignition at 1000°C was used (Gale and Hoare, 1991), the result of LOI (%) experiments of five samples are shown in Table (4). XRD was also run to examine the sample patterns after heating to 1000°C. Heat treatment of the Faidia Clay Member at this temperature caused collapsed and most of the reflections of the clay minerals were destroyed ( Figure 10).

2-Ethoxyethanol Ethylene Glycol Monoethyl Ether (EGME), Surface Area Test
Total surface area is fundamental property of layer silicates and has been used as a criterion for identification. This has been used to determine the total surface area of Faidia clay samples, to determine the retention of EGME the procedure followed Carter et al., (1965). Pure smectites have surface area of 800 m 2 /g, other clay minerals such as Kaolin < 40 m 2 /g and non-clay mineral (including quartz) < 5 m 2 /g (Moorlock and Highly, 1991;and Inglethorpe et al., 1993). The surface area values of the Faidia Clay Member compared other clay standards are illustrated in Table (5).

Swelling test
Swelling efficiency of the clay raw material used the Christidis and Scott (1993) procedure. Natural smectite clay s range from strongly swelling to non-swelling depending on the smectite clay species and on the ratio of exchangeable calcium ions. It is usual in industry to convert the non-swelling to swelling clay by treatment with soda ash (sodium carbonate, Morgan, 1994). An amount of sodium carbonate between 1 to 6 % by weight were mixed with Faidia clay samples (< 125 µm fraction size). A moderately swelling bentonite will swell to a volume of 15 -20 ml., and a good bentonite to of about 25 ml. An excellent grade will swell to 30 ml. or more (Inglethorpe et al.,1993). The Faidia clay showed unchanged swelling power. Table 6 shows the results for the Faidia clay in comparison with other clay standards.

Cation Exchange Capacity (CEC)
CEC can be measured by a variety of methods and to some extent the result obtained is dependent on the method used. The cation exchange capacity of relatively pure smectite clays between 70 to 130 meq/100g (Odom, 1984 Survey for measurement of CEC was used. Table (7) gives the results for Faidia clay compared with Wyoming bentonite.

Discussion and Conclusion
The source of Hematite and Anatase in the Faidia Clay Member; − Chemically, the main result of the alteration of ilmenite mineral is an increase in (formation of co-existing different phases) TiO 2 , Fe 2 O 3 and a decrease in FeO. When the ilmenite is oxidized at a certain temperature the structure breaks down into rutile/anatase and hematite. With increasing degrees of alteration ilmenite disappears and the ratio of TiO 2 :Fe 2 O 3 increases until the altered grain becomes rutile/anatase (Temple, 1966). Hematite in Faidia Clay Member was found filling pore spaces and fractures. A porous anatase mineral was observed with pores filled entirely by clay minerals. The alteration of ilmenite is responsible for the formation of the hematite and anatase minerals in the Faidia Clay Member. The explanation is based on Flinter (1959); Temple (1966); Cambell (1973); Grey and Reid (1975); Anand and Gilkes (1984); Deer et al., (1992) and Babu et al., (1994). The alteration of ilmenite in the Faidia clay took place in two stage processes; 1) all iron oxidized and diffused from ilmenite leaving pseudo-rutile in which closely packed oxygen layers remain intact and 2) the alteration pseudo-rutile dissolves. Iron is removed by solution and both rutile/anatase (TiO 2 ) and hematite Fe 2 O 3 precipitate, according to the following reaction: There is a perched aquifer in the Faidia clay quarry, which may aid the alteration of ilmenite mineral. The area of Umm Ar Razan is highly fractured effects by faulted and jointed area, which may hydrate iron during hydrothermal alteration and removed it as a mobile hydroxide. − The nearest volcanic source is at least 500 to 600 km away to the southwest and southeast. Therefore, it is likely that the Faidia Clay is of secondary origin. The primary volcanic ash is altered to montmorillonite and then redeposited in marine environment. Alternatively some of the montmorillonite may be authigenic (formed in situ), it may derived during the eruption of these volcanoes at that time, it varies in thickness at some parts (lenses like) and provides a suitable high grade montmorillonite. Whilst the majority of the other parts are not suitable for mud drilling fluids (bentonite).
− The Faidia clay samples appear similar in most parts and in commercial terms are relatively low grade (46% montmorillonite), with calcium as the dominant exchangeable cation. − The Faidia clay in fraction size < 2 µm may be suitable for use as mud drilling fluids and water drilling wells at certain depth where low pressure and temperature. − The Faidia clay may use if mixed as a raw material with bentonite (Standard) and treated using chemical additive like sodium carbonate (Soda ash). − The presence of non-clays (impurities) affects the rheological and physical properties and detracts from the commercial performance of the Faidia clay. The Faidia Clay Member has relatively high amounts of Fe 2 O 3 and CaO, whereas the SiO 2 , Al 2 O 3 and Na 2 O are low compared with other commercial bentonites. The Faidia clay is nonswelling clay and did not achieve the necessary specifications compared with standard. Possible future uses are in foundary moulding sand, floor decorations, water and waste water treatment, agriculture, bleaching and animal feed industries. Huge reserves are available for more suitable types of industries, where bentonite enrichment is not critical parameter (use in low value applications).