Lecture 4 - Petroleum Geology and Coal PDF

Lecture 4 Petroleum Geology and Coal Source: Lecture From Mr. G. Ansay and Lecture from DOE (PETROLEUM EXPLORATION, DEVELOPMENT, AND PRODUCTION IN THE PHILIPPINES) Sedimentary Basin  BASIN  Include both the depression and the sediment  BASEMENT  A complex igneous and metamorphic rocks in conti...

Lecture 4 Petroleum Geology and Coal Source: Lecture From Mr. G. Ansay and Lecture from DOE (PETROLEUM EXPLORATION, DEVELOPMENT, AND PRODUCTION IN THE PHILIPPINES) Sedimentary Basin  BASIN  Include both the depression and the sediment  BASEMENT  A complex igneous and metamorphic rocks in continental areas  Negative relief with respect to their surroundings  PLATFORMS OR SHELVES  Areas that receive a normal veneer of sediment over the basement  Neutral relief  ARCHES  Receive thinner than average sediment  Persistent regional positive relief Sedimentary Basin Sedimentary Basin  Geometry of Basin  Vary widely both in size and shape  At least 1000 sq. kms  2- 10 kms in sediment thickness  Vary in shapes (circular, elliptical, rectangular)  Some are embayments that open out into larger basins and lack closure  Basin is not always thickest at its depocenter (Sometimes)  Carbonate basin deposition takes place along shallow shelf margins? (Sometimes)  Tectonic Settings  Convergent Margin  Divergent Margin Sedimentary Basin  Types of Basins According to tectonic Settings (In the Philippines)  Backarc Basin  Moderate to high geothermal gradient  Typified by volcano-clastic reservoirs  Forearc Basin  Limited hydrocarbon potential  Low geothermal gradient  Scarcity of good clastic reservoir  Rift Basin  Insufficient trap size  High geothermal gradient  Inadequate development of source rocks Sedimentary Basin  Types of Basins According to tectonic Settings (In the Philippines)  Backarc Basin 1. Visayan Basin 2. Southeast Luzon Basin 3. Cagayan Basin 4. Cotabato Basin 5. Sulu Sea Basin  Forearc Basin 1. Ilocos Trough 2. Central Luzon Basin 3. West Luzon Basin 4. West Masbate-Iloilo Basin 5. Agusan-Davao Basin 6. Bicol Shelf 7. East Palawan Basin  Rift Basin 1. Northwest Palawan Basin 2. Mindoro-Cuyo Platform 3. Southwest Palawan Basin 4. Reed Bank Basin Sedimentary Basin  Other basin Classification Sedimentary Basin Petroleum  Petroleum Geology refers to the specific set of geological disciplines that deals with the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels.  Chemistry (Geochemistry) – mineralogical composition of rocks and pore-fluid chemistry  Physics (Geophysics) – structures involved in trapping and data gathering in wells  Biology (Biochemistry, Paleontology) – transformation of plants & animals into hydrocarbons and fossil life Petroleum  Petroleum Comes from the word “Petra” means rock and “Oleum” means oil and essentially made up of hydrocarbon compounds.  Forms at normal temperature condition:  Liquid (Crude Oil)  Gas (Natural Gas)  Solid (Tar and Bitumen)  Characteristics:  Its color varies from green, yellow, black or brown  Its sulfur content  Sweet Crude Oil – with little sulfur content (Eg. Matinloc and Cadlao Oil)  Sour Crude Oil – with high sulfur content Composition by Weight Element Percent Range, % Carbon 83 to 85 Hydrocarbon 10 to 14 Nitrogen 0.1 to 2 Oxygen 0.05 to 1.5 Sulfur 0.05 to 6 Metals < 0.1 Petroleum  Origin of Petroleum  Organic Theory Hydrocarbon were derived from the geochemical conversion of organic matter and material in time through the agents of temperature and pressure • • Stage 1 Deposition of plant and animal remains • (marine or terrestrial) • • Stage 2 Burial, pressure and temperature changes • (HC kitchen and maturity) Petroleum  Origin of Petroleum  Organic Theory • • Stage 3 Migration: controlled by lithology, structure • • Stage 4 Entrapment (timing) and accumulation in reservoir rock (porous and permeable) Petroleum  Petroleum System a concept that encompasses all of the disparate elements and processes of petroleum geology  Elements of Petroleum System  Source Rocks (shale, marl, carbonate) – sedimentary rock containing organic material, which under heat, time, and pressure was transformed to liquid or gaseous hydrocarbons  Migration – movement of generated hydrocarbons from the source rock to the reservoir rock in a trap through conduits Petroleum  Elements of Petroleum System  Reservoir Rocks (sandstone, limestone/dolomite, fractured rocks) – any rock that has sufficient porosity and permeability to permit the storage and accumulation of crude oil or natural gas under adequate trap conditions, and to yield the hydrocarbons at satisfactory flow rate upon production  Cap Rocks/Seals (chalks, shale, clays, etc.) – an impervious or impermeable bed capping the reservoir rocks in a trap  Trap – any barrier to upward movement of oil and gas, allowing either or both to accumulate  Timing – relationship between the time of trap formation and time of hydrocarbon generation and migration Petroleum  Elements of Petroleum System Petroleum  Source Rock: Intoduction  Oil and gas come from organic matter through transformation processes involving heat and geologic time.  Oil and gas is generated from organic matter that is preserved in sedimentary rocks Petroleum  Source Rock  It is a rock capable of generating oil and gas  To meet this requirement, the rock must be:  Rich in organic content (Organic Matter)  Matured enough to expel the oil or gas  The rock, therefore, must be a sedimentary rock But what is this organic matter we are talking about? Petroleum  Source Rock  Organic Matter (OM) • refers solely to material composed of organic molecules in monomeric or polymeric form derived directly or indirectly from the organic part of organisms. • Mineral skeletal parts (shells, bones, and teeth) are not included • Ultimate source or all organic matter was originally atmospheric CO2, which was outgassed early in the earth’s history by volcanic activity.  PHOTOSYNTHESIS • is the basic process that accomplishes the mass production of organic matter on earth. • It converts light energy to chemical energy by the transfer of hydrogen from water to carbon dioxide to produce organic matter in the form of glucose and oxygen. Petroleum  Source Rock: Organic Matter  PHOTOSYNTHESIS • Through photosynthesis, some of the CO2 in the atmosphere was converted to organically bound Carbon and free O2 • About 2 billion years ago, in the Pre-Cambrian, photosynthesis emerged as a worldwide phenomenon laying the foundation for the evolution of higher forms of life.  Organic Matter Timeline of Production • From Pre-Cambrian to Devonian, primary producer of OM was marine phytoplankton • Devonian onwards, increasing amount of primary production from terrestrial sources • Presently, production from both are equal Petroleum  Source Rock: Organic Matter  4 MOST IMPORTANT CONTRIBUTORS OF OM IN SEDIMENTS • An increasing diversity of marine life and development of terrestrial plant life through geologic time saw an greater variety of OM. Therefore, several varieties of OM types have been preserved. 1. 2. 3. 4. Phytoplanktons Zooplanktons Higher Plants Bacteria • Contribution from higher organized animals such as fishes is negligible (WHY?) Petroleum  Source Rock: Organic Matter  The production, accumulation, and preservation of organic matter are essential for the existence of petroleum source rocks  PRODUCTION OF OM  Controlled by light, temperature and chemical composition of sea water.  Large part of biological production is concentrated in the upper 60 to 80 meters of the water column.  Productivity of coastal waters 2X as that of open seas. Most productive are areas with water upwelling. Petroleum  Source Rock: Organic Matter  PRODUCTION OF OM Petroleum  Source Rock: Organic Matter  ACCUMULATION AND PRESERVATION OF OM  Practically restricted to an aquatic environment  Balance between energy level and sedimentation rate are needed to concentrate and preserve OM in sediments.  Too high energy level causes erosion and high sedimentation rate  Too low, very little sediment supplied to bury the OM  In general anoxic environments tend to preserve OM while oxic tend to destroy OM  Fine-grained sediments more favorable than coarse-grained sediments  Favorable conditions found in continental shelfs of quiet waters such as lagoons, estuaries and deep basins with restricted circulation Petroleum  Source Rock: Organic Matter  The primary productivity of OM in aquatic environment is presently in the same range as in terrestrial environments.  In terrestrial environments the free access to air and presence of moisture allows growth and action of bacteria. Hence a breakdown and destruction of OM.  In aquatic environments deposition of fine-grained sediments limits access of oxygen. Aerobic bacteria activity stops when oxygen is exhausted  Almost all OM is preserved and fossilized in sediments associated with aquatic sediments.  Through time and elevated temperature, the OM is transformed to kerogen and bitumen. Petroleum  Source Rock: Organic Matter  Kerogen  It is the organic material in sedimentary rocks which is insoluble in ordinary organic solvents.  Formed primarily from carbon, hydrogen, oxygen, nitrogen and sulfur.  Bitumen  It is the organic material in sedimentary rocks which is soluble in ordinary organic solvents.  It is the oil-like part of OM which is mobile.  It is a product of the partial conversion of kerogen as a result of rising temperature and passing time  It has a lower molecular weight compared to kerogen. Petroleum  Source Rock: Organic Matter  Kerogen is the most important to the petroleum geologist.  Majority of all oil and gas comes from the thermal maturity of kerogen. 1. 2. 3. 4. Types of Kerogen Type I. Algal kerogen or alginite Type II. Formed from lipid components or exinite Type III. Woody kerogen or vitrinite Type IV. Eroded or reworked OM or inertinite  Kerogens are typed based on their H,C and O content. Petroleum  Source Rock: Type of Kerogen  TYPE I KEROGEN  Consists of mainly of waxy and cuticular material rich in lipids  Derived largely from algal material or from OM enriched in lipids due to microbial alteration  Hydrogen -rich  Represents the smallest volume of preserved OM but generates the most oil for a given volume of kerogen  Oil will be generated Petroleum  Source Rock: Type of Kerogen  TYPE II KEROGEN  Similar to Type I but contains less waxy or cuticle material  Derived not only from algae but also other organisms like bacteria, phytoplankton, zooplankton and minor amounts of terrigenous OM like spores and pollen  Hydrogen -rich  More abundant than Type I but generated a large volume of the world’s oil and gas deposits  Oil and gas will be generated Petroleum  Source Rock: Type of Kerogen  TYPE III KEROGEN  Contains few, if any, ester groups or alipatic chains  Derived from terrestrial higher plants and their parts including wood, cellulose, lignin, vitrinite and huminite  Hydrogen -poor  Along continental margins where there is rapid deposition  Gas will be generated  (Coal is considered a Type III kerogen) Petroleum  Source Rock: Type of Kerogen  TYPE IV KEROGEN  Contains highly oxidized inertinitic material  Result of either oxidation of OM during deposition or degradation due to diagenetic transformation  Original OM can be from any source but in many cases from Type III  Only gas during the later stage of maturity Petroleum  Source Rock: Type of Kerogen Petroleum  Source Rock: Evolution of Organic Matter  As sedimentation and subsidence continue, temperature and pressure increase. This changing environment changes the structure of the kerogen. The kerogen reaches a higher more stable degree of ordering. Transformation of OM in sediments & sedimentary rocks Petroleum  Source Rock: Evolution of Organic Matter THE THREE MAIN STAGES OF THE EVOLUTION OF OM 1. Diagenesis 2. Catagenesis 3. Metagenesis  With burial, OM undergoes biologic and chemical transformation. Petroleum  Source Rock: Evolution of Organic Matter  Diagenesis  Occurs at shallow depths - first tens or hundreds of meters and low temperatures.  Microbial activity and compaction predominate.  Transformation starts with the following:  Biochemical degradation  Polycondensation  Insolubilization Petroleum  Source Rock: Evolution of Organic Matter  Diagenesis  Occurs during the first million years.  Although it starts early in the geologic history and at shallow depth, it is probably the most important stage.  It is during this stage that composition of the kerogen and geochemical fossil is determined  Microbial action during diagenesis is fundamental in transforming plant debris into a product capable of producing oil. Petroleum  Source Rock: Evolution of Organic Matter  Catagenesis  This process starts with continuous burial and the OM is exposed to increasing temperatures.  Microbial activity ceases.  Level of temperature increase depends upon the geothermal gradient, which is the heat flow generated in the earth’s interior.  Kerogen and geochemical fossils undergo further chemical transformation.  It is during this stage that oil, wet gas and methane is produced.  This is the principal zone of oil and wet gas formation. Petroleum  Source Rock: Evolution of Organic Matter  Metagenesis  Follows catagenesis as a result of continuation of burial and heating.  Occur at great depths - usually greater than 15,000 ft. (4,600 m.).  At this great depth, the kerogen starts to crystallize.  Coal transforms to anthracite.  Sediments buried for a long time - 200 to 400 million years.  Production of methane from kerogen or “cracking” of hydrocarbons occurs at this stage.  Methane is stable at any depth that can be reached by drilling  This stage is of no interest to petroleum geology. Petroleum  Source Rock: Evolution of Organic Matter Generalized scheme for oil & gas generation as a function of thermal maturity of source rocks. Petroleum  Source Rock: Evolution of Organic Matter Petroleum  Thermal Maturity  refers to the extent of time-temperature driven reactions that convert sedimentary organic matter (source rock) into oil, wet gas, and finally to dry gas and pyrobitumen. Petroleum  Thermal Maturity: Determination  Vitrinite reflectance (Ro)  The reflectivity of the coal associated with the source rock is analyzed.  The most common method used to determine thermal maturity.  Thermal Alteration Index (TAI)  Alteration of coal associated with the source rock Petroleum  Organic Richness (% Organic Carbon Rating) Poor Fair Good Very Good Excellent Shale Carbonate <0.5 0.5-1.0 1.0-2.0 2.0-4.0 4.0 + <0.25 0.25-0.50 0.5-1.0 1.0-2.0 2.0 + Petroleum  OM Vs. Particle Size Size Ave. Wt (%) OM Siltstone 1.79% Clay (2-4 microns) 2.08 Clay (less than 2 microns) 6.50 Petroleum  Major source rocks and % of world’s petroleum occurrence Shale 65 % Carbonate 21 % Marl 12 % Coal 2% Petroleum  Source Rock: Summary  Photosynthesis is the process responsible for organic matter produced  When they die, they accumulate in the soil or sea bottom  Proper balance between sedimentation rate and energy level preserves the organic matter in the sediments  Almost all the organic matter preserved are in fine-grained sediments deposited in aquatic environments  Only about 0.1% of the organic produced has been preserved Petroleum  Source Rock: Summary  At shallow depths and low temperatures, microbial activity breaks the OM producing methane gas and hydrogen sulfide in a process called diagenesis.  Continued burial and increase in temperature causes cessation of biological activity and onset of thermally-driven activities in a process called catagenesis. Either oil and/or gas will be formed depending on the OM transformed.  The hydrocarbon generated is expelled form the source rock into carrier beds (primary migration). From the carrier beds it further migrates until trapped (secondary migration).  With further burial and heating of the source rocks, oil and gas (wet) “cracks” to methane (dry gas) in a process called metagenesis. Petroleum  Source Rock: Summary  Effective Source Rocks should satisfy three geochemical requirements:  Quantity or amount of organic matter  organic richness  An Attained Level of Maturity  have hydrocarbons been generated? oil or gas?  Certain Quality or type of organic matter  organic matter type; oil prone or gas prone? Petroleum  Source Rock to Reservoir Rock  Once the source rocks have been sufficiently ‘cooked’, hydrocarbons will be generated and migrates to areas of lower pressure or updip  Migration – the expulsion of generated hydrocarbons from the source rocks to the carrier bed or reservoir rock Petroleum  Source Rock to Reservoir Rock  Types of Migration  Primary – movements of the expelled hydrocarbons from the source rock to carrier bed. It is within nonreservoir rocks and takes the longest time  Secondary – movement from carrier bed to the reservoir  Tertiary – movement from one reservoir to another Petroleum  Source Rock to Reservoir Rock  Migration: Porosity and Permeability  Can be enhanced artificially by:  Acidization – HCl is injected, dissolving the cement of the reservoir  Fracturing – liquid with sand is driven into the reservoir under high pressure  In order for the reservoir to be commercially productive, it must contain an appreciable volume of hydrocarbons, and it must flow at a satisfactory rate when penetrated by the well Petroleum  Reservoir Rock  Rocks that are porous and permeable that can store hydrocarbons coming from the source rocks  Oil and gas is trapped in the porous spaces of a reservoir rock; usually sandstone or limestone. As is the case with source rocks, the reservoir rock must also be permeable so that the hydrocarbons can flow to the surface during production. Most common types of reservoir rocks 1. Sandstone – 60% 2. Limestone – 39% 3. Others – 1% These lithologies host almost all of the world’s oil reserves Petroleum  Reservoir Rock  Sandstone Reservoir  Most important reservoir rock  Majority of grains must be hard, stable, insoluble, w/o crystal characteristic  Contain quartz as an important constituent  Quality of sandstone as initially deposited depends:  Source area  Depositional process  The environment of deposition  Sand exist where there is sufficient relief to supply it Petroleum  Reservoir Rock  Sandstone Reservoir: Provenance  3 principal types according to initial composition:  Dominated by detrital quartz (high-quartz sands)  Containing significant quantities of unweathered feldspar (arkoses)  High content of rock fragments or clay matrix (greywackes)  Why is feldspar undesirable in sandstone? Petroleum  Reservoir Rock  Sandstone Reservoir: Provenance  High-quartz sands:  Cratonic interior of low relief where sands are derived from basement or older sedimentary rocks  Tectonically quiescent continental margin  Newly risen fold thrust belts  Feldspathic or arkosic sandstones:  Uplifted granitic or gneissic basement  Intrusive rocks in interior basins  Rift zones with rapid erosion  Greywackes:  Magmatic arc terranes  Reservoir Rock Petroleum  Sandstone Reservoir: Depositional Environment  Terrestrial (aeolian or dune sands)  Well sorted, adequate porosity  Source of hydrocarbon is less likely to be available  Cross bedded, w/ rounded grains  Fluvial (river deposits)  Deposited by rivers, nonmarine  Rest on erosional surface or unconformities  Common in braided section, w/ many channels and meander belts  Less well sorted than marine sands  Vertical succession of strata is fining upwards  Contain carbonaceous debris  High permeabilities Major sandstone reservoirs  Deltaic – deltaic distributary mouth  Coastal bar and channel sands  Deep marine (turbidites)  Reservoir Rock Petroleum  Carbonate Reservoir  Limestone and dolomite  40% of world oil reserves  30% of world gas reserves  ( all others are in sandstone reservoirs)  Environment  Shallow, tropical, marine waters  Factors controlling carbonate sedimentation o Warmth o Light o Water movement  Reservoir Rock Petroleum  Carbonate Reservoir: Non-skeletal Components  Lime muds- textural designation for all carbonate sediments of essentially clay-particle grain size  may be directly organic or wholly detrital  by accumulation of the remains of microscopic organisms  Coated grains – formed by deposition of CaCO3 around any nucleus  Fecal pellets – formed by worms ingesting lime mud to feed on its content of organic matter  Lumps – aggregation of grains  Detrital grains – or intraclast, may be abraded or redeposited  Reservoir Rock Petroleum  Carbonate Reservoir: Carbonate Depositional Model  Carbonate Shelf Model  Commonest model deposited on the flanks of cratonic mass, continental margin, or other tectonic or depostional features  Deposited in very shallow marine water  Where sediment production exceeds subsidence rate, carbonate sediments accumulate up to approximate sea level  Carbonate ramp model  No prominent break in slope  Facies belt tends to be broader  Much less common  Represent the earliest depositional stage in the development of a typical carbonate shelf model  Reservoir Rock Petroleum  Carbonate Reservoir: Carbonate Depositional Model  Carbonate shelf model thru time  Reservoir Rock Petroleum  Carbonate Reservoir: Carbonate Platforms  Carbonate ramps  Homoclinal ramps  Distally steepened ramps  Rimmed carbonate shelves  Depositional or accretionary shelves  Bypass margins  Erosional margins  Isolated platforms (bahama type)  Drowned platforms  Reservoir Rock Petroleum  Carbonate Reservoir: Nonmarine Settings  Carbonates are traditionally considered as marine  Indicate deposition in continental setting  It has stratigraphic and diagenetic implications  Lacustrine carbonates are important source rocks  Reservoir Rock Petroleum  Carbonate Reservoir: Nonmarine Settings 1. Lacustrine  Commonly deposited in freshwater lakes  In varying area and depth  Lacustrine lithofacies  Profundal facies – mostly varved lime muds and terrestrial clays occupying lake centers o rich source rocks for oil  Littoral carbonates – fringe the lake, lower amounts of clays, higher proportion of skeletal carbonate debris  Fresh-water marl - formed in shallow lakes & marshes o Requires periodic ponding of fresh water in shallow ponds developed on exposed carbonate platforms  Reservoir Rock Petroleum  Carbonate Reservoir: Nonmarine Settings 2. Carbonate dunes  composed of carbonate grains  onshore winds transport the carbonate grains  no particular grain type since wind transports whatever sediments are available  may be com posed of ooids, pellets, foraminifera, etc..  terrestrial fossils are useful indicators  cross-bedding dipping landward indicates eolian origin  Reservoir Rock Petroleum  Carbonate Reservoir: Nonmarine Settings 3. Caliche  forms in semi-arid to arid alkaline soil zones by reprecipitation of low-Mg calcium carbonate  evaporation is involved  occurs as vertically zoned profiles  contains four (4) rock types 1. compact crust or hardpan 2. platy or sheetlike 3. nodular-crumbly 4. massive-chalky  Reservoir Rock Petroleum  Carbonate Reservoir: Nonmarine Settings 4. Cave deposits  Cave or karst-related  Indicators of substantial sea-level drop or tectonic uplift, exposure and action of vadose & phreatic processes on carbonate rocks  Reservoir Rock Petroleum  Carbonate Reservoir: Coastal Settings  Limits – highest storm tides and 5 m below low tide level  Deposits can form in:  Beaches along the windward edges of reefs  Narrow thin beaches or tidal flats  Protected shelf lagoons  Carbonate Reservoir: Shelf Settings  Covers the largest area of modern carbonate deposition  Contains the greatest volume of ancient carbonate sediments  Seal or Cap rocks Petroleum  Lithologic unit which significantly impedes the flow of hydrocarbons, specifically a rock that has pore throats too small and poorly connected to allow the passage of hydrocarbons  Any rock can act as a seal  Major Type of Seals  Shales – 65%  Evaporites – 33%  Carbonates - 2%  Petroleum Trap  It is a configuration of a rock body that constrains the movement of the fluid in the reservoir  What are the types of traps? 1. 2. 3. Structural Stratigraphic Combination  Types of traps and their % of world petroleum occurrence 1. 2. 3. 4. 5. 6. 7. Anticlines Faults Salt diapirs Unconformities Reefs Other stratigraphies Combination 75 % 1% 2% 3% 3% 7% 9%  Trap Structural Petroleum Stratigraphic  Petroleum Trap Structural  Timing Petroleum  Why is timing important?  The trap must have been formed before or during the migration of the hydrocarbons.  If no trap is present, the migrating hydrocarbons will just move up dip until its movement is constrained.  Retention Petroleum  Why is retention important?  Once trapped, the hydrocarbons can further migrate (tertiary migration) or be altered chemically (biodegraded).  Tertiary migration will drain the oil field while biodegradation will destroy the quality of the oil.  Effect of fractures on a seal  The presence of only one fracture 0.035 mm. (0.0014 in.) wide above a 152 m. (500 ft.) oil column can leak off around 150 million barrels in 1,000 years.  A large field can be easily drained if there are several fractures.  Effect of thief beds Petroleum  Thief beds are rocks with reservoir-qualities that abut the reservoir. When tilted, they will drain the reservoir of the hydrocarbons.  Similar to a straw drawing liquid from a bottle.  ROLE OF FAULTS Petroleum  Faults either aid in the entrapment of hydrocarbons or cause leakage from the trap.  They can be sealing or non-sealing.  Why is biodegradation bad?  Through time, meteoric liquids (usually water) is introduced into the reservoir. It carries bacteria and degrades the oil into a heavy one. Heavy type oils are difficult to produce or sometimes cannot be produced. PETROLEUM SYSTEM REQUISITES OF A PETROLEUM SYSTEM Source rocks rich in organic content that must be buried deep enough in the basin so that the temperature will be sufficient to transform the organic matter into petroleum in a process called maturation. The generated petroleum is expelled from the source rock and migrates into a permeable and porous reservoir rock. A seal must envelope the reservoir rock to prevent it from leaking out to the surface or dispersed elsewhere. A trap should exist so that hydrocarbon can be contained and will accumulate within the reservoir. The timing of migration and trap formation is critical. Once it is trapped, retention is important. Post depositional events should prevent it to further migrate or become biodegraded. All of these must be present and favorably juxtaposed in time and space. If not, there would be no accumulation. HYDROCARBON LOSS DURING MIGRATION Reserves estimation • 3 different techniques – By analogy – By volumetrics method – By performance • Volumetric method – Reservoir rock volume – Average porosity – Fluid saturation • Recoverable reserves Recoverable reserves • Recoverable oil = Vb x θ (1-Sw) x R. F. x K Bo Vb= bulk reservoir volume θ = fractional porosity Sw= water saturation R.F.= recovery factor Bo= formation volume factor K = conversion factor Recoverable reserves • • • • • Vb – bulk reservoir volume or closure area x reservoir thickness x net/gross ratio θ - porosity 1-Sw – percentage of pore space not occupied with water R. F. - fraction of in-place hydrocarbon that can be recovered Bo,Bg – factor by which oil shrinks or gas expands between downhole/surface conditions computation • • • • • • • • • Area of closure = 3.212 Acres Average reservoir thickness = 922 feet Gross reservoir volume = Net/gross ratio = 0.5 Porosity = 16 % Oil saturation = 0.62 Formation volume factor = 0.2 Recovery factor = 10% Conversion factor = 7758 barrels/acre ft What is petroleum extraction? • Petroleum extraction is the process wherein usable petroleum is extracted and removed from the earth. • For the sake of simplicity, extraction is divided into five stages. These are PROSPECTING, DRILLING, PRODUCTION, TRANSPORTATION and REFINING. STAGE I: Prospecting • • • The process of prospecting for petroleum can take many paths before a well is ready to be drilled. Geologists use seismic surveys to search for geological structures that may form oil reservoirs. Also, five elements must be present for an oil and gas prospect to be successful. They are: SOURCE ROCKS, MIGRATION, TRAPS, RESERVOIR AND SEAL ROCKS STAGE I: Prospecting • • • Anomaly – prospect generation begins with the search of anomalies, a deviation from whatever trend is normal;  a local feature that standout because of a distinctive fingerprint  Can be revealed by geologic mapping, geophysical or geochemical data, etc  It is associated with commercial deposits of oil and gas Lead – is an anomaly that can be developed to be a prospect with additional data Prospect – is an anomaly that can be defined with existing data and meets a set of criteria requisite for commercial accumulation of hydrocarbons  such as source rock, reservoir rock, trap of sufficient size STAGE II: Drilling • • • • A drilling rig is used to identify and drill into geologic reservoirs. The oil well is created by drilling a long hole into the earth. A steel pipe is placed in the hole to provide structural integrity. Holes are then made n the base of the wall to enable oil to pass into the bore. Primarily in onshore oil and gas fields, once a well has been drilled, the drilling rig will be moved off of the well and a service rig built for completions will take its place. Finally, a collection of valves called a Christmas tree is fitted into the top. These regulate pressures and control flow. STAGE III: Production • • • • • An oil well is utilized to bring petroleum oil hydrocarbons to the surface. A pumpjack is used to mechanically lift fluid out of the well if not enough bottom hole pressure exists for the liquid to flow all the way to the surface. Usually, some natural gas is produced along with the oil. A well that is designed to produce mainly or only gas may be called a gas well. The production stage (after drilling and completion) is the most important stage of a well’s life. As long as the pressure in the reservoir remains high enough, the production tree (Christmas tree) is all that is required to produce the well. STAGE IV: Transportation • • Petroleum is transported in rail cars, trucks, tanker vessels, and through pipelines. From the outlet valve of the Christmas tree, the flow can be connected to a distribution network of pipelines and tanks to supply the product to refineries, natural gas compressor stations, or oil export terminals. STAGE V: Refining • • • • • • The final stage. Refines petroleum from its natural stage. Variations in the usage of different boiling points used to separate petroleum in different components require the heating of the petroleum to 600 degrees Celsius by pumping it through a furnace. The resulting petroleum gas is then piped into the fractioning lower or distillation column. As the gas rises, different components condense in different heights. The resulting major products after refining are: liquid petroleum gas, gasoline, naphtha, kerosene, diesel fuel, fuel oils, lubricating oils, paraffin wax, bitumen, and petroleum coke. Coal Occurrences in the Philippines Outline • • • • Coal Classification and Constituents Overview Geology Coal Districts – Potential Resources and Quality Coal Classification and Constituents • What is coal? Coal (C135H96O9NS) is simply the altered remains of originally lush vegetation which existed at various intervals from 50 to 350 million years ago. • Organic rock which mostly consist of macerals (carbonaceous materials evolved from various botanical components of the initial vegetative debris during coalification) Coal Classification and Constituents Coal is classified according to its quality and rank (i.e. lignite, subbituminous, bituminous, semi-anthracite and anthracite) and is identified according to the extent of coalification. Overview • The Philippines have about 2,370 million metric tons (MMT) of estimated coal resource potential with about 200 MMT in the mineable reserve category. • More than 40% of the mineable reserves have been estimated for the Semirara Island by detailed exploration. • South Mindoro, the Sibuguey Peninsula (Lalat and Malangas Areas) and the Samar-Leyte area comprises 15% of the total mineable reserves. Overview • Lignitic to Semi-Anthracitic with the bulk categorized as Sub-bituminous C and B • Grade ranges from low (1% or less) to high (>3%) sulfur, and low (< 8%) to high (more than 15%) ash • Over 70% comprises lower heating value (9,000 Btu/lb, as received) Geology ► Faults, Folds and intrusion resulted in a wide range of coal rank ► Generally speaking – as the quality of coal increases, difficulties of exploration and development are multiplied Rise in coal quality is attributed to igneous and other geological activities Geology ► Structural deformation in most known coal areas have dips ranging from 150 to 900 ► Coal beds in most areas are relatively thin, but beds as much as 29 m thick are present in some areas ► Wardell-Armstrong and BED (1985) divided the Philippine coal districts into 6 major coal blocks, namely: Eastern & Western Mindanao, Visayas Basin, Luzon Block, and the Eastern and Western Seaboard Major Coal Blocks in the Philippines Luzon Block Eastern Seaboard Western Seaboard Visayas Basin Eastern Mindanao Western Mindanao Coal Districts – Resources and Coal Quality ► Since the Commonwealth Government, different areas in the archipelago have been identified as coal districts and was then blocked per 1,000 hectare by BED ► Several areas have been named as coal districts but some are considered as coal bearing due to minimal volume of reserves AGE AND RELATION OF QUALITY In-Situ Reserves indicated in million metric tons (MMT) Lower MIOCENE Upper Lower Middle 1.8 Upper 5.0 Middle OLIGOCENE 11.0 Lower 14.0 PALEOCENE 22.5 37.5 53.5 65.0 EOCENE PLIOCENE Upper Lower Upper Radiometric Time Scale COAL (million years) AREA PLEISTOCENE Series Subseries DISTRICT Catanduanes Region 1.2 Quezon-Polilio District 6.0 COAL QUALITY AND VOLUME (ASTM Classification) 165.0 45.0 2.5 11.8 209.0 100.0 4.5 1.0 650.0 336.0 0.7 27.0 230.4 LEGEND: OR AGE Cebu Province Malangas Region Masbate Batan Island Surigao Davao Oriental Negros Province Sorsogon Mindoro-Semirara Isabela-Cagayan Area Quirino Province Samar-Leyte Cotabato High Volatile A Bituminous(Fixed Carbon=69%; 14,000 Btu) - Semi Anthracite (Fixed Carbon=86% to 92%; 14,000 Btu) Subbituminous C (8,300 to 9,500 Btu) - High Volatile C Bituminous (11,000 to 13,000 Btu; agglomerating or non-weathering) Subbituminous C - Subbituminous A (11,000 to 13,000 Btu; weathering and non-agglomerating) Subbituminous C - Subbituminous B (9,500 to 11,000 Btu) Lignite (greater than 6,300 Btu; consolidated) - Subbituminous C Peat - Lignite B (6,300 Btu) Coal Districts – Resources and Coal Quality • Although the country have promising coal resources, the geology and other factors constricts the mineability and exploitation of certain areas