SETP1313 Chapter 2 - Geology & Exploration - PDF

SETP1313/CHAPETR 2: GEOLOGY & EXPLORATION DR. SHAZIERA OMAR Department of Petroleum Engineering School of Chemical & Energy Engineering Faculty of Engineering Universiti Teknologi Malaysia COURSE CONTENTS Rock Types Parameters Controlling Petroleum Occurrence Migration of Petroleum Entrapmen...

SETP1313/CHAPETR 2: GEOLOGY & EXPLORATION DR. SHAZIERA OMAR Department of Petroleum Engineering School of Chemical & Energy Engineering Faculty of Engineering Universiti Teknologi Malaysia COURSE CONTENTS Rock Types Parameters Controlling Petroleum Occurrence Migration of Petroleum Entrapment of Petroleum Oil Exploration Methods  Rock Types: Igneous Rock Igneous rocks - derived from Igneous rocks are crystalline solids which form the Latin word ignis meaning directly from the cooling of magma. This is an fire – fire rock. exothermic process (it loses heat) and involves a phase change from the liquid to the solid state. Rock Types: Igneous Rock Igneous rocks can form either on the Igneous rocks are given names based surface (extrusive igneous rocks – upon two things: composition (what from larva flow ), or deep in the crust they are made of) and texture (how (intrusive or plutonic igneous rocks). big the crystals are). Texture relates to how large the individual mineral grains are in the final, solid rock. In most cases, the resulting grain size depends on how quickly the magma cooled. In general, the slower the cooling, the larger the crystals in the final rock.  Igneous Rock Granite Basalt The other factor is composition: the elements in the magma directly affect which minerals are formed when the magma cools. Example of Igneous Rocks: Granite, Diorite & Gabbro (intrusive), and Basalt, Rhyolite & Andesite (extrusive). Rock Types: Sedimentary Rock Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. This material is accumulated and compacted and cemented together – secondary rock. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution. Particles that form a sedimentary rock by accumulating are called sediment - formed by weathering and erosion of pre-existing rocks.  Rock Types: Sedimentary Rock There are 3 main types of Clastic sedimentary rock: sedimentary rocks: clastic, a) Clastic sedimentary rocks are accumulations of clasts - little pieces of broken up rock which have compacted and chemical and organic cemented. sedimentary rocks. b) Clastic rocks are composed largely of quartz, feldspar, rock (lithic) fragments, clay minerals, and mica. c) Example of clastic sedimentary rocks are sandstone, shale, siltstone and conglomerate – classified based on the size of the particles.  Clastic Sedimentary Rock Sandstone Shale Siltstone Conglomerate Continental Environment Mississippi River delta (satellite imagery)  Chemical Sedimentary Rock Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate. Many of these form when standing water evaporates, leaving dissolved minerals behind. Thick deposits of salt and gypsum can form due to repeated flooding and evaporation over long period of time.  Chemical Sedimentary Rock Gypsum Dolomite Example of chemical sedimentary rocks are gypsum, dolomite, halite (rock salt), sylvite and barite.  Organic Sedimentary Rock Coal Coquina Any accumulation of sedimentary debris caused by organic processes. Many animals use calcium for shells, bones, and teeth. These bits of calcium can pile up on the seafloor and accumulate into a thick enough layer to form an "organic" sedimentary rock. Example of organic sedimentary rocks are coal and coquina. Rock Types: Metamorphic Rock The metamorphics get their name from "meta" (change) and "morph" (form). Any rock can become a metamorphic rock. All that is required for the rock to be moved into an environment in which the minerals which make up the rock become unstable and out of equilibrium with the new environmental conditions. In most cases, this involves burial which leads to a rise in temperature and pressure. The metamorphic changes in the minerals always move in a direction designed to restore equilibrium. Common metamorphic rocks include slate, schist, gneiss, marble and quartzite.  Metamorphic Rock Slate Schist Marble Gneiss  Parameters Controlling Petroleum Occurance 1) Source Rocks Refers to rocks from which hydrocarbons have been generated or are capable of being generated. They are organic-rich fine grained sediments that may have been deposited in a variety of environments including deep water marine, lacustrine and deltaic, and under low energy, reducing conditions. The most important factor in the generation of petroleum in source rock is temperature: 225o to 350oF (107o and 176oC) - the “hydrocarbon window”. The action of heat on the insoluble organic matter (kerogen) contained in source rocks leads to the formation of oil and gas.  Parameters Controlling Petroleum Occurance 2) Reservoir Rocks A petroleum reservoir is a porous and permeable rock in communication with a mature source bed. Sandstones and carbonate rocks form the overwhelming majority of reservoirs world-wide. Under special circumstances, igneous and metamorphic rocks can also act as petroleum reservoirs. Parameters Controlling Petroleum Occurance 3) Traps An arrangement of rock layers that contains an accumulation of hydrocarbons, yet prevents them from rising to the surface. Consists of an impermeable layer of rock above a porous, permeable layer containing the hydrocarbons. It can be structural traps or stratigraphic traps or combination of these factors. Structural traps occur when the reservoir formation deforms. Stratigraphic traps are those where porosity or permeability has changed within a formation. Migration of Petroleum Oil and gas move out of the source The transfer from source rocks to beds and accumulate in the reservoir rocks is called primary reservoir rocks. migration Movement of petroleum within the The primary cause of primary porous and permeable reservoirs migration is compaction and diffusion beds is known as secondary – due to differing concentrations of migration. fluids in source rock and the surrounding rock thereis a tendency to diffuce. Migration of Petroleum The more permeable silt and sand The primary cause of secondary bodies within compacting shale are migration is buoyancy forces. These the main channels of fluid forces are proportional to the migration. density difference between hydrocarbon and water. Primary migration is slow and proceeds over short distances, while secondary migration is faster and can proceed over very long distances (more than one-hundred kilometers).  Direction of fluid migration into anticline. Migration from an Migration of interbedded shale-sand Petroleum sequence.  Migration into a pinnacle reef. Migration Migration of into stratigraphic Petroleum traps. Migration of Petroleum Migration of Petroleum  Oil, gas and water slowly migrate through permeable rocks, driven by natural forces of gravity (buoyancy) and pressure gradients. When they meet an impermeable barrier, they can go no further, so oil and gas accumulate. This barrier is generally referred to as a trap. Entrapment Varying densities make the gas phase rise, while the of Petroleum water settles to the lowest point, and the oil remains in the middle. Traps may be classified according to the manner in which they are formed, and categorized as structural trap, stratigraphic trap and combination trap.  Anticlinal oil traps Caused by faulting The greatest number of fields discovered world-wide and the largest proportion of total proven reserves are associated with structural traps. Structural traps resulted from a local deformation such as folding and/or faulting of the rock layers. Faulting can also produce traps by juxtaposing a reservoir against an impervious stratum.  Sediment draping Draping or compaction over a buried hill, carbonate reef also produces traps on a smaller scale.  Stratigraphic Traps Stratigraphic traps are depositional in nature. This means they are formed in place, often by a body of porous sandstone or limestone becoming enclosed in shale. The shale keeps the oil and gas from escaping the trap, as it is generally very difficult for fluids (either oil or gas) to migrate through shales. Stratigraphic trap is a general term for traps that are formed as a result of a lateral and vertical variation in the thickness, texture, porosity and lithology of the reservoir rock, or a break in its continuity. A permeable reservoir rock changes to a less permeable or to an impermeable rock. Stratigraphic Traps Examples of this type of trap are pinchout and truncated type.  Combination Trap The geometry of this type of trap is the result of a combination of tectonic processes and changes in lithology. A common trap that would be an example of a combination trap is a salt dome. Salt dome Petroleum Traps Oil Exploration Method In the early days of petroleum, most oil finds were the result of digging or drilling near known oil and gas seeps or of accidental finds while drilling for water. A good definition of a seep is ''the surface expression of a migration pathway, along which petroleum is currently flowing, driven by buoyancy from a sub-surface origin'‘. At the most basic level, this demonstrates that the basin contains a generating source rock and hence a viable petroleum system. Surface Geology - Remote Sensing Method The selection of effective exploration targets is an important step to achieve success in oil exploration. Remote sensing refers to using infrared or other means to map an area. This method is used to study the basic of petroleum geological conditions. The remote sensing images have characteristics of realty and provide accurate visual data for directly determining geometric shapes of sedimentary basins. Surface Geology - Remote Sensing Method The remote sensing techniques are more effective and useful for understanding and studying those basins in the out-of- the-way mountains and remote deserts. Remote sensing equipments can be carried by airplanes or by satellites. Companies using remote sensing data, however, still need traditional exploration information to pinpoint the location of commercial deposits.  Surface Geology - Remote Sensing Method The visible bands The edge of the Andes penetrate water and Mountains is seen show suspended flanked by extensive sediment in surface alluvial fans that form The White Sands are dunes water. Volcanic relatively flat surfaces. composed of gypsum sand blown mountains are visible from a nearby dry lake bed. In around the lake. this image the gypsum dunes appear light blue, and the sand source area is dark blue. Geophysical Exploration 1- MagneticMethod Sedimentary rocks generally have a very small magnetic susceptibility compared with igneous or metamorphic rocks, which tend to have a much higher magnetite (a common magnetic mineral) content. By conducting a magnetic survey over a given area, a prospector can determine where oil-bearing sedimentary rock is more likely to be found. The magnetometer is used to measure the magnitude of the earth's total magnetic field over a large area. Magnetic Method A magnetometer can be towed behind a ship or an airplane to cover large areas. It transmits data to a device on board which records the information onto paper or magnetic tape. A development of airborne magnetics is the micromagnetic technique for oil exploration. An airplane tows a micromagnetometer from a low altitude, normally about 300 ft above the ground. It detects micromagnetic anomalies, or deviations from the norm. Geologist use these data to predict the characteristics of the overlying sediments.  Geophysical Exploration 2- Gravity Method The Earth's gravitational attraction varies slightly from one place to another on the Earth's surface. Some of this variation occurs because the Earth is not a perfect sphere, and some is related to differences in elevation on the Earth's surface. For example, in north-central Kansas, there is an anomaly known as the Midcontinent Gravity High where the Earth's gravity is about 0.006% greater than normal. In gravity prospecting, geophysicists measure variations in the force of gravity from rocks up to a few miles beneath the earth's surface.  2- Gravity Method Different types of rocks have different densities, and the denser rocks have the greater gravitational attraction. If the higher-density rock formations are arched upward in a structural high, such as an anticline, the Earth's gravitational field will be greater over the axis of the structure than along its flanks. A salt dome, on the other hand, which is generally less dense than the rocks into which it is intruded, can be detected from the low value of gravity recorded compared with that measured on either side. 2- Gravity Method These aircrafts are installed with gravity system which can reduce cost of operations.  Geophysical Exploration 2- Seismic Method Seismic reflection, a powerful technique for underground exploration, has been used for over 60 years. It will give more precise details on the formations beneath the surface. Seismic waves are essentially sound waves that travel underground at velocities of 2 to 4 miles per second (3 to 6 km per second), depending upon the type of rock through which they pass. The reflections are recorded by detecting instruments responsive to ground motion (geophones). They are laid along the ground at distances from the shot point which are generally small compared with the depth of the reflector.  2- Seismic Method Variations in the reflection times from place to place on the surface usually indicate structural features in the strata below. From the geophones, the wave will be send through cables to a recorder. The recorder, a seismograph, amplifies and records the wave characteristics to produce a seismogram. Seismograms generate a seismic section, which is a two-dimensional slice from the surface of the earth downward. The information from a seismic survey indicates the types of rock, their elative depth, and whether a trap is present Onshore Seismic Operation Offshore Seismic Operation Offshore Seismic Operation Offshore Seismic Operation Interpretation of Seismic Data Interpretation of Seismic Data 2-D Seismic Interpretation Interpretation of Seismic Data 2-D Seismic Interpretation  Interpretation of Seismic Data 3-D Seismic Interpretation  Interpretation of Seismic Data These enlargements with high- resolution seismic clearly show the channelling system within the reservoir as well as the location of saturated sand. Sub-surface Geophysical Exploration - Well Correlation Consists of establishing correlations by matching strata, rock hardness or softness, and electrical and radioactivity data to determine the origin, composition and distribution of rock strata. Electrical logs, radioactivity logs, and acoustic logs help geologists predict where oil bearing strata occur. Sample logs, compiled from well cuttings and cores, are used to identify key beds and lithologic sequences. Sub-surface Geophysical Exploration - Well Correlation Core samples are taken from the top to the bottom of a well and shows rock in sequential order as it appears in the ground. Core samples also provide information on porosity, permeability, and saturation of rock in the well. Cuttings are not a continuous record like core samples, but provide a means for identifying sections within larger thick layers through fossil and mineral deposits. Well Correlation Thank You !