Migration and accumulation of oil

Deepchand Vinod

Migration and accumulation of oil

Deepchand Vinod

visibility

…

description

33 pages

link

1 file

AI-generated Abstract

This paper discusses the processes of migration and accumulation of petroleum, focusing on both primary and secondary migration mechanisms. Key factors influencing these processes include capillary action, bacterial action, differential specific gravity, and hydraulic movement. The paper highlights how different geological conditions affect the distance of oil migration and provides schematic diagrams to illustrate the concepts, contributing to a better understanding of petroleum reservoir dynamics.

Migration and accumulation of oil Deepchand V Department of Geology University of Kerala deepchandgeology@gmail.com Contents • Introduction • Primary Migration. • Secondary Migration. • Distance of oil migration • Accumulation of oil • Summary Introduction • Petroleum is highly disseminated in source bed after conversion from buried organic matter. • At last it become concentrated in oil fields in large quantities. • The movement or migration of petroleum are two types • Primary Migration and Secondary Migration. Primary Migration The movement or migration of petroleum from the source beds in to carrier beds is known as primary migration. Secondary Migration The movement from carrier bed to suitable trap beds is known as Secondary Migration Introduction • Movement of oil and gas through rock depends on • • • • • • • Compaction Capillary action Differential Specific Gravity Hydrostatic Pressure Cementation Pressure from volume increase by salt precipitation Diastrophic movements Fig. 1 Schematic diagram showing Primary and secondary migration and accumulation Source: Slideshare.com Primary Migration • Primary migration Resulted by Compaction bacterial action Capillary action Primary Migration 1. Compaction It is the compaction with in the source bed act as an important principle of migration of oil or gas Compaction of shaley materials cause reduction of its porosity (90 to 35%) it leads to the rock become impermeable. Primary Migration 2. Capillary action Important part. mud or shale saturated with oil will come contact with sandstone saturated with water Due to high surface tension water will move out of coarse grained sandstone to finer shale or sand This causes the dispersion of oil in to neighboring sand stone This action increase with increase in temperature Effective in tabular openings having diameters between 0.002mm and in sheet opening between 0.001mm and 0.25mm Primary Migration 3.Bacterial action Bacteria release oil from sedimentary materials This is done by dissolution of limestone or dolomite by carbonic acids produced by bacteria's. oil formation and creation of void space to migrate oil are occur at the same time. Viscosity of oil decreased by increase in carbon dioxide. Produced CO2 also increases gas pressure which helps to move oil through interstitial openings Secondary Migration • Flow of oil from carrier rock to trap rock • Any porous strata through which petroleum may have moved is known as carrier bed (Rich et al) • CB are wide spread • Sst./ Lst./ weathered or dissolved surface of Lst. beneath an unconformity. Fig.2 Schematic diagram showing carrier bed. Source: Fig.3 Schematic diagram showing source rock , carrier rock and oil migration. Source: slideshare Secondary Migration • Permeability may reduced by compaction, cementation and recrystallization • If beds exposed at surface permeability may increase due to deposition, fracturing, solution and weathering Secondary migration may caused by 1. Differential specific gravity 2. Hydraulic movement 3. Differential gas pressure 4. Cementation 5. Diastrophic movements 1.Differential specific Gravity • • • • • • • • • • Important migration through carrier bed. Oil has less density than water. So it has a tendency to rise up on water. This migration takes inside the reservoir rock. And occurs during the structural evolution of entire rock formation. This process generally termed as gravitational process. Leads to stratiform arrangement of oil, gas and water. The water is generally connate water. Gravitational effect is due to difference in specific gravity of oil and water. If there is no water gravity cause oil to migrate down in dip direction and accumulated in synclinal folding. Fig.4 Density difference between oil and water. Source: google images Fig.5 Oil accumulated in a synclinal folding Source :http://geologylearn.blogspot.in 2.Hydraulic movement or currents • Subsurface water current flush oil along with them. • This accelerate oil migration. • These currents formed by compaction or artesian water circulation. • Artesian water circulation helps in large scale migration in large area. • Another way is that oil move in water as emulsion. • Mill’s view : water escape through natural openings such as faults and fissures has induced hydraulic currents through the carrier bed. Fig. 6 Subsurface movement of water Source: USGS Fig.7 emulsion Source: google images 3.Differential gas pressure • In migration of oil and gas differential pressure is usually an aid to other factors such as capillarity, differential specific gravity etc. 4.Cementation. • Deposition of cementing material within carrier beds or reservoir beds has played important role in migration and accumulation of oil and gas. • Deposition of cementing materials in sst cause movement of water with oil and gas in the direction of least pressure. • Porosity of sst decreased by precipitation of crystalline minerals in pores. • The partial or complete elimination of voids result in expulsion of any contained fluid or gas. • The fluid and gas contained within carrier beds migrate in the direction of low pressure Fig.8 Pore spaces are filled by cementing material Source: quora.com Fig.9 5.Diastrophic movements • According to Daley force resulting from diastrophic movements are the most important cause of oil migration and accumulation. • Lateral thrusting of a petroliferous basin would compresses the area and anticlinal folds would be formed normal to the direction of the forces. • The synclines would be more compressed than the anticlines • The contained liquid would have a tendency to move from more or less compressed areas. • Results in the concentration of liquids farther from the point of application of pressure. • Mills regards fissures caused by faulting and joints of the rocks has considerable importance in migration and accumulation. • Release of pressure due to faulting causes gas oil and water to rush towards the faulted areas. • Some gas tends to escape through fissure and oil accumulate adjacent to it. Fig.10 Different types of diastrophic movements and resultant oil migration. Source : google images. Distance of Migration • It is the most controversial subjects on petroleum geology. Movements have been restricted to relatively short distance (100 Ft. or Few miles) Movements have been restricted to 10x miles or 100x miles. • Most available evidence favours short distance migration. • Factors determine distance of migration of oil and gas are Areal distribution Permeability Continuity of reservoir beds Distance of Migration • Movement occur in highly permeable and uniform carrier bed in long distance under ideal conditions • Wide areal distribution • Differential hydrostatic pressure • Arguments favour of short distance migration. • Changing porosity of rock • Change in structures like fault fold and other breaks. Distance of Migration Fig.11 Schematic diagram showing distance of migration of oil Source : GAEA Accumulation of oil • Migration of oil leads to accumulation. • It is the collection of oil droplets in pools. • Concentrated accumulation is required for commercial oil pool. • Accumulation depends upon reservoir rocks and traps. • Oil may migrate with out accumulation. Or • Oil may accumulate in a non commercial body. Accumulation of oil Oil pool • concentration of petroleum in a source rock. • It is also known as underground lake of oil . • It is porous rock saturated with oil. • Oil pools are formed under certain conditions Availability of sedimentary rock (predominantly marine and unmetamorphosed) Should have adequate source rocks in which the petroleum has been formed. Reservoir rock should porous and permeable Should have an impervious rock layer called cap rock overlying the oil bearing strata. Accumulation of oil • Underground occurrence of petroleum may be classified as Oil pools Oil fields Oil provinces Accumulation of oil • Oil pools • Underground occurrence of petroleum in a single separate reservoir on a single natural pressure system. • Oil or gas deposit of a single deposit • The production of petroleum in one part of the pool will affects the reservoir pressure through out the extent • Pool is bounded by geological barriers Accumulation of oil • Fields. • Consist a single pool or two or more pools. • It is commonly related to a same geological structure. • For example in the case of a salt dome structure, where more than one pool is present in the same field. • Different fields are separated by one another. • Different fields occur in different stratigraphic horizons • Different field are separated by impermeable strata. • Filed may associated with small domes , anticlinal folded strata and combination of faulting, folding and stratigraphic variations. Accumulation of oil • Provinces. • This is a region in which a number of oil and gas pools occur in similar or related geological environment . • This term is used to include the larger producing regions. Summary • Migration of oil are of two types; Primary and Secondary. • Primary and secondary migration depends upon several factors and again devoid of several types. • There is a controversy between long and short distance migration of oil. • Distance of oil migration is controlled by several factors. • Accumulation of oil is the collection of oil droplets in pools. • Underground occurrence of oil is mainly as pools, province and fields.

Log In

Migration and accumulation of oil

Sign up to get access to over 50M papers

Sign up for access to the world's latest research

Related papers

Related papers

Related topics

pFad - (p)hone/(F)rame/(a)nonymizer/(d)eclutterfier! Saves Data!