Fundamentals of petroleum Oil and gas introduction (5) The university of Texas at Austin-petroleum extensive services 1.1 :the basic concepts of geology :the origin of petroleum :types of rocks and their formations :the importance of porosity and permeability :how reservoir pressure influence flow -The science of geology deals with the origin, history, and physical structure of the earth and its life as recorded in rocks formations and fossils. Uses: to predict where oil and gas accumulation may occur in commercially viable quantities. They look for evidence of locations of ancient rivers, deltas, beaches, and oceans and try to decipher how these feature shifted with time Used in com-bent with astronomy, chemistry, biology and physics Petroleum geologists job : 1. They reconstruct the geological history of an area to find likely locations for petroleum accumulations 2. They find one of these locations and evaluate it to determine Whether it contains enough petroleum to be commercially Productive In reality a petroleum reservoir is a rock formation that holds oil like a sponge holds water Reservoirs can be broad and shallow or narrow and deep BASIC CONCEPT OF GEOLOGY Core- made up of the heaviest components, mainly iron and nickel Scientists know that the core is made up of two parts: Inner solid core(5100km) and Outer liquid core(2900km). Both under extreme pressure and temperature Mantle- lighter materials form a thick solid mantle around the outer core Crust- made up of lighter minerals such as, aluminum, silicon, and magnesium. - 8% sedimentary covers 75 % of the lands surface - 27% metamorphic - 65% igneous In geology : - earth is 4.6 billion years to 600 million - no plants animals - 4 billion year long pre-Cambrian period - earth is 600 million year to 220 millions years - first diversity of plants and animals. - 380 million years long Paleozoic era - earth is 220 million years to 70 million years- more than half of world plant and animals reserves in this time period - 150 million years long Mesozoic era - earth is 70 million years to present - extinction of dinosaurs raising of the Rockies ice age in northern hemisphere - 70 million year long centazoic era PLATE TECTONICS Provide the basis of how continents and formations are formed. Imagine large jigsaw puzzle pieces floating on water. In some places slide past one another and on top and below. Oceanic crust- under the ocean- oceanic crust is thin about 8 to 11 km and is made up of primarily rock that formed when molten rock, Called Magma, Cooled down. Continental crust- under the continents surface- the rock of continental crust is much thicker about 16to 48 km and relatively light, as a result continents float above oceanic rock like an iceberg would drift in an ocean An example of plate tectonics is the mid Atlantic ridge. A place between Iceland and the southern tip of Africa, it has a deep rift or trench along its crest, suggesting a place where two of the greatest plates are dividing or moving apart. Each time one erupts it pushes out molten rock that cools and new crust is form between the two plates. - Rifting These collisions between tectonic plates are what cause earthquakes and volcanos and tsunamis and most of the earths major disasters.. GEOLOGICAL STRUCTURES The continuous movement of the earths crust over millions of years has changed the shape of land masses and oceans, we can prove this by taking sample of rock that are on top of the highest peaks of mountain ranges and the deepest wells and see that they were once apart or ancient seas that rose or fell to their current positions now today. Geologists determine two basic structures that occur when rocks deform or change to shape due to tectonic movement: 1. Folds 2. Faults At the surface of the earth rocks tend to be weatheringand be stationary until the break due to great stresses such as earthquakes, however in the deeper parts of the crust the heat that rises from the mantle raises the temperature of the rock and the pressure of over laying rock compresses the rock formations below. At higher temperature and pressure rock formations tend to warp and bend rather than break when stressed. FOLDS - folds are strata that have crumpled and buckled into wavelike structures. - folds are the most common structure in mountain chains, ranging in size from wrinkles of less than and inch to great arches and troughs many miles across. - folds are recognized as rocks that are not flat but dipped or curved ANTICLINES- anticlines are the Arches SYNCLINES - synclines are the Troughs FAULTS- when rock near the surface break, the two halves might move in relation to each other, producing a fracture known as a fault Faults are generally classified by the direction that they move. In normal and reverse faults the movement is usually vertical. In strike slip or lateral faults movement is horizontal. Overthrust and growth faults usually have a combination of both horizontal and vertical movement. These faults are important to geologists because their movements are what creates the accumulation of oil and gas. Normal - earth is eroding down Reverse- earth is being pushed up Thrust/ overthrust - earth is being shifted up or down and side to side Lateral- earth is being shifted horizontal Growth- combination of vertical and horizontal Faults can produce recognizable features such as: GRABENS - a graben is a long narrow block of crust between two faults that has sunken relative to the surrounding crust. - the opposite would be a :HORST, a Horst is a block of crust that has risen An example where to find this type of mining is in the North Sea, sediment-filled grabens beneath the ocean floor can be found with rich supply of hydrocarbons. ORIGIN OF PETROLEUM PRODUCTS Geologists theorize that about 1 to 1.5 billion years after the Earth was formed small organisms and micro bacterial developed in water and made its way to the oceans through streams and rivers. More complex forms did not appear in abundance until the beginning of the Cambrian period(550 million years ago). Not only until the Devonian period(350million years ago) did vegetation become widespread on the earth. Land animals were relatively rare until much later on. The history of our planet, Earth, is essential because according to the prevailing theory, organic matter is necessary for the formation of oil. CATEGORIZING ROCKS - igneous :: rocks are formed when molten magma cools and solidifies. - sedimentary :: rocks formed from sediment in a horizontal layering called strata - metamorphic :: were originally igneous, sedimentary or other metamorphic rocks that were buried deep in the earth and subjected to high temperatures and pressures. Deep in the earths crust temperatures and pressures become extreme. Hot enough to melt rock turning into Magma, Water is a crucial ingredient in the formation of sedimentary rock. Also sediment might be composed of minerals that participate out of water. limestone, sandstone and shale are all examples of sedimentary rocks. Among others wind and temperature Metamorphic meaning meta meaning after or beyond. And morph, meaning to change form or shape. During the metamorphic process, the original rock undergoes physical change and chemical change that greatly alters its composition and appearance. For example limestone can be metamorphosed into marble and sandstone can turn into quartzite A unit for one type of rock in a layer is called a ; formation THE ROCK CYCLE Wind water and moving ice erode all types of rock. These moving particles are carried to the ocean or lakes creating new sedimentary rock. The movement of magma into rock into new rock creates igneous rocks when it cools it cools and metamorphose the existing rock with its heat. Tech tonic plates movement raises buried rock to the surface, eroding it or pushing it further into the earth where it metamorphose or becomes magma. PETROLEUM BEARING ROCKS -most oil and gas accumulations occur within sedimentary formation -most of the oil lies in sedimentary rock formed from marine sediments deposited on the edge of continents. Such as Gulf of Mexico and Persian Gulf. It is uncommon for igneous and metamorphic rocks to contain oil and gas. Hydrocarbons must be generated in the sub surface,trapped within reservoir rocks, and remaining in place until they are produced. Each one of these 3 steps take millions of years. The organic theory- states that oil and gas come predominantly from the remains of organic material (microscopic) they would have been carried by river and lakes to oceans and died mixing in with sand mud and silt. The a biogenic theory consists of oil and gas being pre arranged in the earths crust This is a rich, organic mixture that we call Kerogen. -kerogen is rich in hydrogen and carbon. This mixture was cut off from any oxygen In the water. With no oxygen the organic material could not decay. Layers and layers of sediments were deposited on top of each other as time passed. The great pressure of above sediment caused changes to the lower layers turning loose sediment into rock. Increasing pressure also increases the temperature. As temperatures increase to 150 degrees Fahrenheit 66 degrees Celsius the kerogen has began to recombine with hydrogen molecules.. By the time kerogen-rich rocks often called source rocks. are hot enough to produce oil, up to 300 degrees Fahrenheit they are in the stage of the oil window. Above 300+ degrees Fahrenheit the heavier long chain molecules break into smaller lighter hydrocarbons such as methane gas. Geologists refer to this stage as the gas window. Further layering (overburden rock) will increase the temperature and pressure. Once at 500 degrees Fahrenheit the hydrocarbons are destroyed a swell as the source rock Rocks seem to be solids to the naked eye, yet if you magnify them you will see that some rocks have pores. A rock thats has pores is considered to be porous. The porosity can be measured. This is an example of rock holding oil such water would be held by a sponge. Porosity may vary from 5% to 30% in urn consolidated formations or sands. To be commercially valuable most of the rock should have a 10% porosity level or greater. This number varies on rock type and the amount of fracture in the surrounding drill area. A rock would be considered to be permeable when the pores of a rock connect. This allows the oil gas and water to move freely from one pore to another. The unit of measurement of permeability is Darcy. Most oil wells drilled require a measurement to measure the permeability which is so small we use millidarcies which measure the Darcy to thousands. Hydrocarbons mixed in with low permeable rock have a hard time flowing through the rock which makes it difficult to drill. Ex shale -sandstone and carbonates such as: limestone, dolomite are generally the rock formations with the greatest permeability (porous and permeable rocks) -shale is a rock that is not porous practically no permeability. If it does have pores it is called shale oil or shale gas. Different technologies such as fracture type drilling and horizontal type drilling has allowed for more success rates at jobs such as shale oil/gas. Very long chains of hydrocarbon molecules are much more restrictive in flow, higher viscosity, and are sometime referred to as tar. If the reservoir is made up of a sandstone it would be referred to as tar sand. (Ex. Fort Mac.) Water in the upper layers of the crust is essential to the extraction and migration of moving hydrocarbons towards the surface. The oil and gas have a natural buoyancy in the water allowing these products to settle on top of the water brings the pressure up from the water acting as a solvent below. .With all of the water involved with such a high mineral dissolved content it cannot be considered fresh water. TRAPS -a trap is an arrangement of rock layers containing a accumulation of hydrocarbons where the formation prevents the hydrocarbons from rising to the surface. - Contains impermeable layering of rock above porous, permeable layering containing the hydrocarbons -the simplest way to group traps is by studying the geological features that cause them to form. Geologists group traps in two types: Structural- occur when the reservoir formation deforms in some way Stratigraphic- are those in which porosity or permeability has changed within a formation or where a non porous, layer seals off the top of a reservoir. Structural traps------- -Anticline -Fault trap - plug traps Stratigraphic traps----- -Unconformity -Impermeable barrier Bio herm Beach/ sandbars Shoestring Lenticular trap Structural Most are formed by the folding or faulting of reservoir rock. Reservoirs formed by folding have the shape of anticlines or domes. In a anti clinical trap the rock layers that were originally formed horizontally are folded upward into each other in an arch or dome. Later the hydrocarbons migrate from below into the porous and permeable rock bed in the anticline or dome and the hydrocarbons accumulated in the top of the folded porous layer. A CAP ROCK - a layer of impermeable rock above the reservoir sealed off the reservoir and stopped further movement. A PLUG TRAP- a dome with a core- called a plug usually the plug is makeup of non porous salt that has pierced deformed or lifted the overlying strata. - Where hydrocarbons can migrate into any porous and permeable rock beds on both sides of the column of salt and be trapped there, unable to flow into the salt. The plug can be circular such as the us coast or long and narrow such in the Romanian oil fields. -The discontinuity can make plug traps difficult to drill successfully. Recent discoveries and advances in drilling are improving these standards when tapping a reservoir associated with plugs A fault trap - formed by the movement of rock along a fault line. The reservoir rock is on one side of the fault. - in one type of fault trap the other side is an impermeable layer opposite the reservoir that prevents hydrocarbons from migrating further - in another type the permeable material is a rock called a gouge within the fault- zone itself. -A fault trap depends on the effectiveness of the seal that that gouge or impermeable layer provides Petroleum in a fault tends to accumulate lengthwise parallel to the fault trend Stratigraphic -a stratigraphic trap is caused either by ---a non porous formation sealing off the top edge of a reservoir bed or by change of porosity and permeability within the reservoir bed. -A lenticular trap is also considered by a stratigraphic trap--- ------- lenticular trap------- ----caused by a change of permeability within a rock layer , abrupt changes in the amount of connected pore space seal off the hydrocarbons in the more permeable part of the bed These changes might have been caused by an uneven distribution of sand and clay as the sediment was being deposited. Unconformity-- this process is when earth layers eroded and new deposits of rock settle on the existing layers to form younger layer of rock.. The time gap between these layerings is known as unconformity. Geologists distinguish 3 types of unconformity: - non conformity -- an unconformity where the older, eroded rock is igneous and the new layering is sedimentary - dis conformity -- an unconformity where the old and new rock layers are parallel to each other - angular unconformity -- the older rock below the unconformity that has deformed before the overlaying rocks were deposited. This causes two strata to be tilted relative to each other Combination trap It is common to have reservoirs trapped by a combination of folding, faulting, permeability changes And other conditions A fluid is any substance which will flow. Reservoir rock contains 3 different types of fluids : gas oil water Oil and water are fluids as well as liquids gas is a fluid but not a liquid in its natural state. Lightest on top : gas Middle: oil Heaviest on bottom: water Petroleum geologists prefer that the reservoir they dig for have all 3 layers. The water creates pressure from pushing towards the surface anything in between (oil/gas) Most oil reservoirs are sedimentary formation that were deposited in or near the sea. ----(H2O)---- Originally saturated with salt water ---- some of the water evaporates or gets pushed to surface. The salt water that remains is called Connate Interstitial Water --Connate water is the water that stayed in the formation when the petroleum reservoir was being formed. It is this free water that supplies the energy for a water drive. Bottom water occurs beneath the oil accumulation and edge water is found at the edge of the oil zone. Wetting water- a film sticks to or is absorbed by the solid rock material surrounding the pore space In other words water is not only in the ground beneath the oil reservoir but inside the oil reservoir with the permeable rocks in the formation. There is the rare occurrence of 100% saturation of oil in the reservoir and have no film of water lining the pores. Natural gas Reservoirs usually contain gas as well with the oil. In two principle ways: Solution gas: solution gas stays in solution until a well is drilled into the reservoir Free gas: gas that is not dissolved in the oil tends to accumulate in the highest structural points of a reservoir Dissolved gas Lowers the viscosity of the oil making it easier to flow to the well head Geologist want to find the oil-water and gas-oil contact line. We do this to get the maximum out of the well without pumping water. The same goes for oil and gas but the gas does not naturally mix with oil as easily as the water in oil. All fluids under ground are under pressure. When abnormal pressure occurs the weight of the formation on the top of the reservoir adds to the fluid pressure. Fluid pressure is similar to the pressure in a swimming pool. The deeper you go the greater the pressures Once connection to the surface has been made with the reservoir it is considered safe and is controllable. ( in most cases) In some cases when a reservoir is drilled oil can be pushed through the top of the Derrick due to higher water elevation in the reservoir than the Derrick 1.2 Collecting Data Geophysics: the application of certain physical properties to the science of geology ( this involves magnetism, gravitational pull, velocity of sounds waves and behaviour of electrical currents) Surveys Magnetic - measure the earths magnetic pull exerted on a instrument that is flown over the area to be surveyed Gravitational - thicker, deeper basement rock (less sedimentary) will read higher than on the land based instrument that is driven over the surveyed area. Seismic - very accurate and detailed - based on the energy waves created by man - made impulses - waves pass through strata of differing density ( porosity ) at different speeds And intensities - very intrusive to the environment - quite expensive - usually a series of 2-D - integrating into a 3-D, or even a 4-D(time) presentation is increasingly Common Vibroseis- a seismic method employing the use of a heavy vehicle under which a large steel pad is mounted, this is the most popular method of seismic method. As the pad is lowered to make contact with the ground vibrations are generated to produce low frequency percussionist waves. Geo phone also used to record the returning impulses. Expensive but less impact to the environment. Due to the controlled nature of the wave generation, can be the most accurate. Drilled logs- systematic complete written showing detailed drilling/geological information and history during the drilling process. Sample logs- cuttings (ie every 5meters) -analyzed and logged - cores 9 meters long provide similar but usually more complete data Wireline logs- a indirect analysis of down hole features and characteristics obtained at a specific depth for some tests or from a range of depths for others. In virgin holes an instrument known as a sonde is lowering on a wire during drilling SP sonde ( spontaneous potential) - a wireline logging sonde used to measure weak natural formations electrical current Restrictively log - another type of sonde which is able to detect Howell a formation is able to conduct induced electrical current. Acoustic / sonic logs - measures how quickly induced sound travels through the porosity of a reservoir rock which may help in determining the formation that is being tested Drill stem test (DST) - a procedure for testing a formation through drill pipe - often defined as temporary completion of a well to determine the fluid content of a reservoir and its ability to produce Stratigraphic correlation - may be made as a result of gathering information from various sources, comparing data from a known, proven source, with that of geological theory. The decision of whether one prospect presents more likelihood of a success than another rests on many factor the main one of course being geology - the geological factors that may be considered may be : - geological location ( very I portent) - proximity to the market, whether the rights can be obtained, and Physical Barriers,
Posted on: Sun, 14 Sep 2014 07:36:38 +0000
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