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Lab Report 7 by Andrew Grant

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Introductory lab for petroleum engineering
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  1 The University of Trinidad and Tobago, Point Lisas Campus Esperanza Road, Brechin Castle, Couva. Executive Summary The main purpose of this experiment was to become familiar with the different type of sedimentary rocks provided in the lab. In order to classify and identify these rocks according to their characteristics and nomenclature, various materials, equipment and apparatus were employed to expedite the required objectives of the lab. These objectives were to determine whether or not the rock samples provided were either sedimentary or mineral in character. As well as to ascertain whether the samples given were good or poor hydrocarbon source rock or reservoir rock. Moreover, analysis of the sedimentary rock samples were performed using the Moh’s Hardness Scale as well as hydrochloric acid (HCl). Hydrochloric acid was used in order to determine whether or not the sample contained minerals or chemical / biochemical sediment fragments or grains. From the results obtained, it was possible to determine which type of sedimentary sample rock would constitute a good/poor hydrocarbon source rock or reservoir rock.  2 The University of Trinidad and Tobago, Point Lisas Campus Esperanza Road, Brechin Castle, Couva. Objective/Aims: 1.   To ascertain from the ten samples given, which are sedimentary or mineral rocks via rock analysis and a classification table. 2.   To identify each sample rock using the following: a.   Reaction with dilute HCl  b.   Moh’s Hardness Scale c.   Physical Appearance using a magnifying glass. 3.   To distinguish with justification from the ten samples given, which sample constitutes a good/poor hydrocarbon source rock or reservoir rock. Theory:  Rocks are important to the petroleum industry because they provide source beds and reservoirs for petroleum. They consist of aggregates of minerals in various proportions and are identified by their origin and composition (Link, 2001). Differentiation of rock types is on the basis of their srcin, which can be igneous, metamorphic, or sedimentary. Rocks formed from materials derived from pre-existing sources that are transported deposited are termed as sedimentary rocks. They may result from the accumulation of  particles weathered from rock exposures, transported and eventually deposited, many accumulate by precipitation from solution, or may accumulate from precipitation from skeletons or life processes of marine animals and plants. Sedimentary rocks can be classified according to environment of deposition, rock type, or by srcin. They are classified as follows: Detrital/Siliciclastic sedimentary rocks  –   consisting of the weathered remains of rock fragments, quartz, feldspar and clay grains. Examples of detrital sedimentary rocks are mudstones, sandstones, shale, conglomerates, breccias etc. Chemical sedimentary rocks - consisting of inorganic rocks such as limestone, dolostones, evaporates, chert and precipitates (gypsum). Biochemical (bioclastic)  –   consisting of fragments or shells of organisms (plants or animals), such as biogenic limestones, coal and peat (Lab Manual, 2007).  3 The University of Trinidad and Tobago, Point Lisas Campus Esperanza Road, Brechin Castle, Couva. Since sedimentary rocks come from many sources that can produce nearly identical lithologies, a combination of classification criteria will be used for this experiment. Some of these measures are listed as follows: Physical properties i.e. colour, texture, grain size, hardness, surface cleavage, lusture streak etc. Biochemical properties i.e. reaction with dilute HCl. Apparatus and Materials: Magnifying glass Dilute aqueous HCl Moh ’ s scale of Hardness Kit Procedure: As directed by the lab manual Results: See attached handout  4 The University of Trinidad and Tobago, Point Lisas Campus Esperanza Road, Brechin Castle, Couva. Discussion: The purpose of this experiment was to describe, identify and classify ten sedimentary rocks in hand specimens. With respect to sample one, it was observed that its physical appearance was as follows: The hardness on the Moh’s scale was  2. Its particle size ranges approximately 0.06  m to 2 mm; this sample was classified as a sedimentary rock formed from calcareous  particles. These particles consist of fossil materials, pebbles and granules of carbonate rock, and oolites. The sample was a dense, uniform, fine grained rock with conchoidal fracture. Its colour was reddish brown with very fine visible particle grains. The reddish  brown colour is due to lime mud which contained CaCO 3 , which makes it biochemical (bioclastic) in nature. From the observed description above, sample one was identified as a sedimentary carbonate rock commonly called limestone, but is exclusively called micrite. Micrite srcinated from the recrystallization of minerals such as aragonite and calcite and cemented (a process called diagensis) with lime mud under high temperatures. When the micrite sample was in the presence of hydrochloric acid (HCl), a “fizz” reaction occurred. This test confirmed that the sample was limestone in character. The “fizz” reaction occurred when calcium carbonate reacts with hydrochloric acid to yield  calcium chloride, water and carbon dioxide evolved as shown below: CaCO 3  + HCl ---   CaCl + H 2 O + CO 2  Micrite is a sedimentary carbonate rock, and therefore it is considered to be a good hydrocarbon source rock. These type of limestone contains evaporite deposits under sea water and they also contain significant organic materials such as decayed shells and coral fragments. Organically precipitated rocks are those that come out of solution in response to life processes of marine plants. Marine flora for example, extract carbon dioxide from the sea water and cause precipitation of calcium carbonate, which remains in solution as long as there is sufficient carbon dioxide dissolved in water. Marine fauna extract calcium carbonate and some phosphate minerals from the sea water as part of the metabolic processes involved in forming their shells and exoskeletons. Reefs and banks of fossils and fossil fragments, including shells and corals, form by accumulation of these skeletal materials. Thus rocks form in this manner often have extensive porosity and  permeability and are therefore excellent reservoirs (Link, 2001).

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Jul 23, 2017
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