Porosity and Permeability

Porosity and Permeability
The vast majority of geological materials can hold water to a greater or lesser extent, the amount of water if affected by the materials porosity and permeability. Porosity is a parameter that describes the amount of open space in geologic material, it can be stated as either a fractional value or percentage of the material that is open space. This open space is not however a void like the interior of a balloon it is more like a sponge with small air bubbles and interconnecting pores. These open pore spaces occur between sediment grains, in cracks or fractures and also on a larger scale in cavernous openings formed by dissolution of rock. The porosity values of rock typically range from 0-50%, this space is often filled with water or air or mixture of both. Permeability is closely linked to porosity as permeability is a parameter that describes the ability of geological material to transmit water.
Permeability is measured in Millidarcy (MD) or Darcies (D). A Millidarcy is 1/1000 of a Darcy. A Darcy is the permeability that will allow a flow of 1 cubic centimetre per second of a fluid with 1 centipoise viscosity through a distance of 1 centimetre through an area of 1 square centimetre under a differential pressure of 1 atmosphere. The greater the permeability of a rock, the easier it is for fluids to flow through it. Typical permeability values may range from 1 to 10 MD (poor permeability), 10 to 100 (good), and 100 to 1000 (excellent). However permeability is about the connected pores in rocks, If for example a rock had a high porosity it could still have a low permeability if the pores were not connected so water couldn?t enter them. Aquifers are geological material which transmit large quantities of water, this meaning they have a high permeability. The opposite to an aquifer is an aquatard these have a low permeability. The porosity and permeability of rocks and other geologic materials is hugely important in several fields such as water supply, damming, mining, oil reservoirs and civil engineering. I intend to study the effects of porosity and permeability on oil traps and reservoirs before investigating myself the way it effects a range of rock types. Oil reservoirs and traps Oil is classed as a geological liquid this in essence means that it is a liquid found in rock. Oil is found within the pores of sedimentary rocks, mainly sandstone and course grained limestone?s, It stays trapped in these rocks for millions of years until it is extracted. Oil is made up of primarily dead microscopic sea organisms, these organisms died and sank to the bottom of the sea where they settled along with sedimentary deposits, over time the amount of dead organisms on the sea bottom increased and as they decomposed they formed an ?ooze? like substance as they were mixed up with sand and sedimentary deposits. This ooze was then covered by further layers of shale and other depositants over millions of years which meant that ooze came under a high pressure and also due to the earths internal temperature a high temperature, this mix of high temperature and pressure leads to the decaying organisms being denatured and over a long time period turning into hydrocarbons; oil and natural gas. These hydrocarbons started of as small globules between particles of shale as shown in diagram; Grey = shale Blue= water and/or air Black = hydrocarbons [image] But as pressure is increased by the weight of overlying sediment the hydrocarbons were forced sideways for miles in some cases , the majority of this hydrocarbon were dispersed either as gases to the surface or remain in very low quantities spread over a large area. However some of the hydrocarbons filtered into rock formations like sandstone and limestone where they became trapped thus forming a reservoir of oil. To form such a reservoir the oil must be trapped, to prevent further movement etc. the two main types of trap are structural traps where the rocks have been deformed or faulted in some way and straigraphic traps where the oil is trapped due to porosity of different rock types. Structural traps ==== Anticlines ? If a permeable rock like a sandstone or limestone is sandwiched between impermeable rock layers like shales or mudstones, and the rocks are folded into an anticline, hydrocarbon can migrate upward in the more permeable reservoir rocks, and will occur in the hinge region of the anticline. Since anticlines in the subsurface can often be found by looking at the orientation of rocks on the surface, anticlinal traps were among the first to be exploited by petroleum geologists. [image] Faults ? If faulting can move permeable and impermeable rocks so that the permeable rocks always have impermeable rocks above them, then an oil trap can form. Since faults are often exposed at the Earth?s surface, the locations of such traps can often be found from surface exploration. [image] Salt Domes ? During the Jurassic Period, the Gulf of Mexico was a ?sealed? sea. This resulted in high evaporation rates & deposition of a thick layer of salt on the bottom of the basin. The salt was eventually covered with normal sediments. But salt has a lower density than most sediments and is more ductile than most sedimentary rocks. Because of its low density, the salt moved upward through the sedimentary rocks as salt the sedimentary rocks as salt domes. The intrusion of the salt deforms the sedimentary strata along its margins, folding it upward to create oil traps. Because some salt domes get close to the surface, surface sediments overlying the salt dome are often domed upward, [image]making the locations of the subsurface salt and possible oil traps easy to locate. Stratigraphic Traps ======= Unconformities ? An angular unconformity might form a suitable oil trap if the layers above the unconformity are impermeable rocks and permeable rocks layer are sandwiched between impermeable layers in the inclined strata below the unconformity. This type of trap is more difficult to locate because the unconformity may not be exposed at the Earth?s surface. Locating possible unconformity traps like this usually requires subsurface exploration techniques, like drilling exploratory wells or using seismic waves to see what the structure looks like. [image] Lenses ? Layers of sand often form lens like bodies that pinch out. If the rocks surrounding these lenses of sand are impermeable and if deformation has produced inclined strata, oil and natural gas can migrate into the sand bodies and will be trapped by the impermeable rocks. This kind of trap is also difficult to locate from the surface, and requires subsurface exploration techniques. [image] Reservoir Rock A reservoir rock is one which has a high permeability and therefore usually a moderately high porosity. It is in rocks with these properties that oil can remain in the pores if the reservoir rock is in a oil trap situation. Common reservoir rocks are sandstone and limestone, these are both sedimentary rocks, these are good reservoir rocks as they have a high permeability due to having a high porosity as there are lots of gaps between grains. Igneous rocks, like granite, do not have as higher porosity or permeability this is because they are made of interlocking mineral crystals. (see diagrams) Igneous rock Sedimentary rock [image] It is clear to see from diagrams as basic as these that there are considerable more pores(shown in yellow) in a sedimentary rock than an igneous rock. However to form a rock sediment grains need to be cemented together, this cement can effect the porosity and permeability and therefore the sediments effectiveness as a sedimentary rock. Impermeable rocks like the igneous rock shown are very important in the creation of oil traps as without them the hydrocarbons would disperse or evaporate leaving them in very low concentrations in the reservoir rocks. Impermeable rock ==== Impermeable rocks have either a very low or no permeability and a low porosity, this is generally due to there mineral structure with impermeable rocks often being igneous with interlocking crystals or being extremely well cemented sedimentary rocks, where the cement ?clogs? up the pores between grains. Factors affecting rocks porosity and permeability ============= After looking at the structures of various rock types I have concluded that there are 3 main factors effecting porosity and more importantly to petroleum geologists permeability;
Grain size- the larger the grains are, it is logical to conclude
that the larger the pores between them will be. Also the sorting
of grains as if they are poorly sorted smaller particles could
fill up pores between larger grains.
Rock type- the rock type will effect the type of bonds between
minerals etc (e.g. interlocking crystals) and the type/ amount of
bonds would effect the porosity and permeability.
Amount of cementation- this effects sedimentary rocks, but as this
is the most common type of reservoir rock this is very important
to geologists, if a rock has a higher percentage of cementation
then I have concluded that it will have a lower porosity as the
cement would be filling the pores.
I intend to perform three different basic experiments to see to what extent my hypotheses are correct. Experiment 1; How does rock type affect porosity? ============= In this experiment I intend to study how different rock types affect porosity. I want to see how much water can enter a rock through its surface as this is important to geologists when studying reservoir rocks in oil traps. I intend to use a very basic method, which is as follows; Equipment and justification for usage;
Deep tray- so that the rock samples are completely submerged in
water so that the porosity is for the whole of the sample and not
just for the partially submerged section.
Water( 5 litres per repeat)- this is a the most common geological
liquid, it is easily available and is non toxic so it does not
present a health hazard
Scientific balance- to give an accurate measurement to 0.1 g, this
is important as the changes in mass may not be major
Rock samples from the 3 rock groups(sedimentary, igneous and
metamorphic)- so I can study the porosity of the different rock
groups as they are of differing structures and compositions, also
using multiple samples from the different groups will make it
easier to see trends in the rock groups porosity.
Stopwatch- to ensure accuracy in the timing and therefore
encourage fair testing.
Paper towels- cheap, disposable method of removing surface water
without affecting the water contained in the inner pores.
Method; 1. The tray should be filled with enough water to cover the sample 2. The rock sample is weighed on the balance and the mass, in grams, is recorded 3. The sample is then submerged in the water for 5 minutes 4. The sample is removed surface water is dried off with a paper towel the mass is then measured again. This will be repeated 3 times for each rock sample. Safety == This experiment has few risks and hazards associated with it, I will still however make sure that all standard lab safety rules are followed. As some of the samples I am using are of a reasonably high mass I will be careful not to drop any as this may result in injury. Fair testing ==== To achieve a fair test and therefore limit the chances of anomalous results I will do the following;
Use a stopwatch so that all the samples are submerged for the same
time period (5 min) I will start the stopwatch when the rock is
fully submerged and remove the rock at exactly 5 minutes.
I will repeat the test 3 times for each rock sample so that I can
get an average % porosity, this will mean that if any of my
results are slightly anomalous the average will give a truer
porosity for the sample as the multiple repeats will diminish the
significance of anomalies from individual results.
I will use the same quantity of water for each repeat (5 litres)
this will mean that all the testate?s will have the same water
pressure on them making the test fairer than if the amounts of
water was different for each repeat.
When drying the samples of surface water I will dry them all the
same amount by wrapping the sample in a paper towel and then
removing it as quickly as possible.
I will use fresh water for each repeat as some substances may
dissolve into or be suspended in the water during the test, if I
reused this water it may effect
Simple as this method of measuring porosity is I feel it will be sufficient to give an indication of the differing porosities of different rock types. I think that sedimentary rocks will have the highest porosity and igneous rocks the lowest and metamorphic rocks in between them. I have concluded this by looking at the rocks differing structures; a sedimentary rock is made of cemented grains this means there are gaps between grains and cement. Igneous rocks are crystalline and made of interlocking mineral crystals therefore I think there porosity will be low as, these crystals are bonded very tightly to each other, the gaps present will not be as big or as numerous as between the grains in sedimentary rock. Results === I have carried out my experiment as stated previously in the tables below are my results; Name Mass before (g) Mass after (g) % Mass increase % Average porosity Observations Conglomerate (well sorted) 350.3 414.4 18.30 18.3 Conglomerate (poorly sorted) 386 449.7 16.50 13.84 Pieces fell into water Conglomerate (poorly sorted) 492 547 11.18 Chalk 53.4 66.75 25.00 22.84 Rock went structurally weak Chalk 72.6 87.4 20.39 Water went cloudy Chalk 106.7 131.4 23.15 Shale 176.5 231.2 30.99 30.99 Rock fell apart Sandstone 109.5 125.9 14.98 15.57 Pieces fell into water Sandstone 127.6 149.9 17.48 Sandstone 81.4 93 14.25 Well cemented Quartzite 59.3 61.8 4.22 2.88 Well cemented Quartzite 82.4 83.9 1.82 Well cemented Quartzite 107.3 110.1 2.61 Slate 89.9 90.89 1.10 1.29 Slate 127.3 129.2 1.49 Slate 77.8 78.8 1.29 Schist 227.9 229.9 0.88 -0.02 Schist 280.2 287.2 2.50 Schist 154.6 149.3 -3.43 Gneiss 226.3 229.9 1.59 1.64 Gneiss 59.6 61.2 2.68 Gneiss 126.5 127.3 0.63 Gabbro 289 293.6 1.59 2.65 Gabbro 154 162.2 5.32 Gabbro 327 330.4 1.04 Weathered Gabbro 517 612 18.38 9.91 Rock went very structurally weak Weathered Gabbro 376 398.9 6.09 Weathered Gabbro 296 311.6 5.27 Dolerite 106.5 108.3 1.69 1.73 Dolerite 225 227.8 1.24 Dolerite 216.5 221.4 2.26 Basalt 157.2 160 1.78 1.54 Basalt 222.3 224.9 1.17 Basalt 89.7 91.2 1.67 Obsidian 58.2 58.2 0.00 -3.19 Obsidian 50.5 50.2 -0.59 Obsidian 88.1 80.2 -8.97 The results highlighted in yellow are those that I think are clearly anomalous, these anomalies are most likely due to errors in either reading or the copying down of results. Evaluation of experiment 1 I feel that my results do support my original hypothesis broadly speaking they are not however totally conclusive, below I have listed the problems which I either encountered during the experiment or realised after;
When the rocks are removed from the water they are losing water
and therefore mass as it runs out of the pores, it also loses mass
as its dried on the paper towel. This could reduce the % porosity
The permeability being measured is the effective permeability
instead of the actual permeability, however generally in petroleum
geology effective permeability is more important.
The rocks have surface water present, this is particularly
noticeable on the rougher rocks, this surface water would
unnaturally increase the mass and therefore make my results show
wrong % porosity.
Several of my observations comment on cloudy water or the rock
breaking down, this is due to the gases already in the pores
creating a resistant pressure to the water as the gases are unable
to escape they could widen micro fractures around the pores
increasing permeability and possibly resulting in the rock
disintegrating. This would not only make it very hard to measure
the mass but would also mean that the rocks porosity has been
affected.
There may have been structural changes to the rock due to its
complete emersion under low pressure, Calcium Carbonate (chalk)
for example went very weak and parts became suspended in the
water, yet in situ below the surface chalk beds do not
disintegrate with jointed chalk acting as an aquifer in some
cases, this is possible as the rock is under pressure due to
overburden etc, therefore my experiment is in fact testing
porosity out of situ (e.g. under different pressure) therefore
rocks properties may be different due to the environment its
tested in.
The samples differing sizes and shapes may effect my results even
if they are in average % porosity as the size and shape of the
sample could mean that the rocks structure is different to that of
the rock in situ also this may be unfair if all the rocks of one
type for example are significantly smaller than samples of another
type
If I were to repeat this experiment there are several things that I would change about the way that I carried it out these are listed below;
Performing the experiment in a vacuum as this would solve the
problem of air traps/pressure in the rock, practically however it
would be very hard to set up and perform the experiment in vacuum
without large industrial laboratory equipment.
The use of water as the testing medium has caused several
problems, these are primarily to do with waters surface tension
which can form air traps in pores, one method of solving this
problem is by using mercury, which has very little surface tension
so it can fill all the pores giving a truly accurate effective
porosity, this effective porosity would however only be relevant
to mercury which isn?t a common geological liquid.
To be a totally fair test the rock samples should be of the same
shape and size, this could be achieved by using central sections
from a core bored from the rock.
There are numerous other potential solutions to the major problems which are shown in this experiment, I intend to detail these in my over all evaluation of the investigation. Experiment 2; How does grain size affect the permeability of sediment? In this investigation I intend to investigate if grain size affects the permeability of sediment, I predict that the larger the grain size, the larger the pores will be and therefore the higher the permeability, this is shown in the diagrams below. Despite the stylisation of these diagrams I feel they do still show that the larger the grains the larger the pores would be meaning a higher permeability (although not necessarily a higher % porosity). [image] To prove this hypothesis correct I intend to perform the following simple experiment; Equipment and justification for usage; ? 4 litre plastic drinks bottle- allows a large quantity of sediment and also has space at the top for a reservoir of water. ? 30 cm3 of 5 different sizes of sediment ranging from 0.2-1cm- this range of grain sizes is quite common in sedimentary rocks, it is also coarse enough for the measurement of grains to be accurate, which will encourage a fair test. ? Plastic funnel -to ensure water is not lost during pouring and to act as an upper reservoir ? Clamp stand with boss and clamp ? to hold the apparatus steady during testing so that kinetic energy is not altering the results. ? Stopwatch- to measure time accurately ? Measuring cylinder- to make sure that the amount of water is the same for each repeat ? Water (2 litres per repeat)- this is a the most common geological liquid, it is easily available and is non toxic so it does not present a health hazard ? Tights- to act as a filter preventing sediment leaving the bottle but allowing water to pass through it, they are cheap, commonly available and easy to fix to the bottle. ? Sellotape- to keep a tight seal so that no sediment can leave the bottle during testing [image]Method; ? The equipment should be set up as shown, with one grain size of sediment in the bottle ? Water should then be poured into the funnel, timing should begin when the water makes contact with the top of the sediment ? The water should be poured in as quickly as possible ? When there is no longer any surface water on the top of the sediment and when the flow at the bottom subsides to drips timing should stop and the result in seconds should be recorded. ? This should be repeated 4 times for each grain size ? Then the experiment should be repeated using a different grain size Safety This experiment has few risks and hazards associated with it, I will still however make sure that all standard lab safety rules are followed. I will make sure that the clamp stand is secured firmly so that the apparatus will not fall over when the centre of mass is changed by the addition of water. I will also position the experiment over a sink so that the water that has passed through the sediment does not form a slip/fall hazard on the floor. Fair testing To achieve a fair test and therefore limit the chances of anomalous results I will do the following; ? I will repeat the test 4 times for each grain size so that I can get an average time taken, (which will be an indication of the grain sizes permeability) this will mean that if any of my results are slightly anomalous the average will give a truer time for water flow through the sample as the multiple repeats will diminish the significance of anomalies from individual results. ? I will pour the same quantity of water (2 litres) into the sediment each time this will mean that this is consistent for each grain size reducing the chance of anomalous results. ? The same quantity of sediment will be used for each test; this means that the volume of sediment will not affect my results as it is constant for each experiment. ? The sediments I am using are brought from a reputable commercial supplier; this means that the sizes should be consistent and accurate. ? The large container I am using as a sediment barrel and the use of a funnel should create 2 reservoirs of water(1 in the funnel and 1 on top of the sediment in the bottle) this should give a consistent flow of water, this is vital for the experiment to be fair as the timing starts when the water makes contact with the sediment not when it has all been poured out of the measuring cylinder. Results; ==== I carried out the experiment as I stated above below are the results; Time taken (seconds) Name of rock Grain size(mm) Repeat 1 Repeat 2 Repeat 3 Repeat 4 Average White sand 0.2 840.6 917.4 903.5 898.3 889.95 cactii gravel 2 101.37 34.61 32.68 35.42 51.02 Aggregate 5 38.2 36.16 32.18 31.5 34.51 Aggregate 7 31.01 32.28 33.66 31.85 32.20 Aggregate 10 33.26 33.61 38.35 38.83 36.01 Experiment 2 evaluation ======= After completing my experiment I have decided that there are several issues which have arisen from my simple method which may effect my results I have detailed these below;
The volume of water passing through the sediment is unknown as it
is not collected this means that it is impossible to work out
accurately the Darcy of the sediment as there may be water
remaining in the pores after the experiment
Before the water is added there will be air trapped in the
sediments pores as water starts to flow through the sediment it
may not be able to move through all of the pores as air traps
could form due to the surface tension of water
Water,trapped air
Water could potentially move down the sides of the sediment barrel
as it is not very wide so water could flow down the sides where
gaps would be present due to the difference in texture of the
smooth plastic and the coarse sediment, this means the
permeability given is not a true permeability of the sediment size
as it is effected by the container.
The materials used for each grain size were different this could
have an effect on permeability as the sediment grains are not only
of differing materials so they would have different properties in
there relation to there attraction or repulsion of water they also
would be of different shapes with for example a particle from a
beach is likely to be rounded by its transportation in water,
whereas a particle from a scree slope is more likely to be angular
as it is transported by gravity and forms due to brittle
deformation.
As the same sediment is used for each of the repeats of the
experiment the sediment noticeably reduces in volume as it
compacts, this means the pores are getting smaller as the water
flow/mass effects the packing of the grains. This would obviously
effect the permeability.
The waters movement is effected by five main factors; the funnel,
sediment, filter, bottles shape and the water flow into the
bottle. Of these only one should be a variable the sediment. The
funnel and the top of the bottle act as reservoirs giving a
regular flow of water through out the experiment. The water flow
into the water is effected by the person pouring the water in,
this is significant as if the flow into the funnel is not constant
then the water in the ?reservoirs? will be of differing masses,
the pressure from this would be different which would effect the
rate of water flow through the sediment. The bottles shape is also
effecting the permeability of the sediment, as it effects the rate
of water flow, where the water leaves the bottle acts as a bottle
neck, this means that although all the results are equally
effected by this it means that any calculations performed using
the experiment results are not going to be correct. The filter may
also effect the rate of water flow as it may be smaller than the
pores in the sediment, especially if the sediment is coarse in
grain size, this would mean that the filter would slow the rate of
flow effecting my results.
As I measured the sediment by volume there will be more grains for
a smaller grain size in 30cm3 than for a larger grain size, this
could affect my results as there are more grains for the water to
move through in a smaller grain size than a larger one, this means
that potentially its actually the number of grains which is the
controlled and therefore my method may be generally flawed as my
aim was to investigate grain size.
My experiment is only investigating the permeability of the
sediment in relation to water, this is not the most economically
important geological liquid compared to oil or gas. This
significantly reduces the value of experiment 2, as it is not
necessarily relevant to my original aim, which was to research
porosity and permeability in relation to petroleum geologists.
If I were to repeat this experiment I would do the following to either eradicate or reduce the errors and problems listed above;
To remove air from pores I would wet the sediment before the
experiment so the pores would be filled with water and not air. To
continue making the experiment a fair test I would add the 2
litres of water and then finish timing when 2 litres of water was
collected in a measuring cylinder at the bottom, this would mean
that I would have an accurate rate of flow for 2 litres through a
set quantity of sediment. From this information it would be
possible to work out the permeability of the sediment in Darcy?s.
To resolve the problem caused by packing during repeated
experiments on the same sediment a fresh container of the same
type and size of sediment could be used for each repeat as this
would mean that the average results would be more accurate.
To prevent water travelling down the sides of the sediment barrel
a larger one could be used with the water poured down the centre
this would mean that the results were an accurate permeability of
the central sediment and not effected by the container.
? The problems caused by differing materials for different grain sizes could be resolved by using one ?universal? sediment, which is available in a range of different sizes with a similar grain shape. ? To solve the problem with the filter I could use different sized meshes for the different grain sizes having the mesh as close to the grain size as possible but still smaller than it. This would mean that the mesh would not be effecting the water movement, as it would be larger than the pores in the sediment. ? The problems caused by the flow of water into the funnel being at different rates and for different times due to human error could be solved by using a mechanical pouring device this would mean a steady water flow could be provided for a set amount of time, this would make my experiment fairer by reducing the opportunities for human error. There are numerous other potential solutions to the major problems which are shown in this experiment, I intend to detail these in my over all evaluation of the investigation. Experiment 3; how does the % of cementation affect the permeability of sedimentary rocks? In this experiment I intend to investigate if the % of cementation effects the permeability of sedimentary rocks. As it is complex and time consuming to work out the % cementation of ?natural? sedimentary rocks, I intend to create my own with a closely controlled % of cementation by using Portland cement, I have chosen to use Portland cement as it is reasonably insoluble in a short period of time, this is important as my results would be affected if the cement dissolved in the water. I predict that as the Portland cement is viscous and will therefore stick to the grains so as the % of cement increases the permeability will decrease as the cement will take up more and more of the pore space as it bonds the grains, this would obviously restrict waters flow through the pores. I intend to use the same method as for experiment 2 with a few differences, which I have detailed below; ? Instead of changing the size of grains each time I intend to use the same sized sediment for all of my experiment (7mm aggregate) ? I will add 0-5% of pre made cement (1 part Portland cement powder to 3 parts sand with water) to the sediment mix it in and leave it to set overnight, I will then perform the experiment in the same way as for experiment 2. ? I will then repeat this 3 times for each % of cement Safety As well as following normal lab safety procedures I will also have to take additional precautions as Portland cement is potentially dangerous. Cement powder is an alkaline, it can have a caustic effect when in contact with bare skin for a period of time, it is also toxic. Due to these factors I will wear gloves, safety goggles and a dust mask when mixing the cement, I will also avoid touching the cement with bare skin. Fair testing To achieve a fair test and therefore limit the chances of anomalous results I will do the following; ? I will repeat the test 3 times for each % of cement so that I can get an average time taken, (which will be an indication of the % cementations effect on permeability) this will mean that if any of my results are slightly anomalous the average will give a truer time for water flow through the sample as the multiple repeats will diminish the significance of anomalies from individual results. ? I will pour the same quantity of water (2 litres) into the sediment each time this will mean that this is consistent for each % of cementation reducing the chance of anomalous results. ? The same quantity of aggregate will be used for each test; this means that the volume of sediment will not affect my results as it is constant for each experiment and therefore the only variable is the % of cementation. ? All of the sediment/cement mixes will be left to set for the same period of time so that the cement is equally cured in them all, this means that the state of the cement should be the same for all meaning the results should only be affected by the % ? The grain size and material is constant for all so this should not effect the quality of my results. Results I carried out the experiment as stated above below are my results; Percent of cement Repeat 1 (sec) Repeat 2 (sec) Repeat 3 (sec) Average (sec.) 5% 152 132 160 148.00 4% 122 92 134 116.00 3% 79 68 74 73.67 2% 45 53 40 46.00 1% 38 27 33 32.67 0% 22 35 29 28.67 These results appear to support my hypothesis that the higher the % of cementation the longer it would take for water to move through and there for the lower the permeability. My results also appear to be reasonably accurate with only one possible anomaly (high lighted in yellow) this is probably cause by human error in the recording or reading of the results. Evaluation of experiment 3 All the points I have made in my evaluation of experiment 2 (with the exception of the comments about differing materials for different grain sizes) are valid and relevant with reference to experiment 3, as are my possible solutions to the problems as well as this there are however some problems which are specific to experiment 3 these I have detailed below; ? The % of cement I am using is of a very low volume and as it is mixed by hand for a short period of time the chances are that it is not very well distributed through out the sediment, this means that water could flow through pores and sections of the sediment which have very little or no sediment present. This would make my experiment unfair as the distribution of cement would be different for each %. ? The water which came out the bottom of the bottle was a murky cement like colour the probable cause for this was that the cement had not fully set so some of it dissolved in the water, this would reduce the %of cement in the sediment barrel and therefore change my results. ? The cement has to be left to set overnight otherwise it would not be acting as a bonding agent and would just be a pore fluid present in the sediment. But as cement sets it contracts this causes fractures and faults, during the testing it would be possible for water to travel down these faults which would mean that the results are not an accurate representation of permeability ? The % of cement is not natural when compared to sedimentary rocks and also the human synthesised material is very different in it properties to the matrix which bonds sediment grains in natural sedimentary rocks (for example cement has a higher viscosity meaning it bonds grains in a different way to that which the matrix does when under pressure. This means that the experiment is only testing the permeability of a man made sedimentary ?rock? and would therefore not necessarily have the same properties or the same permeability as a normal sedimentary rock. ? As the cement is added as a % it means that the volume will be different for each of the cementation percentages (e.g. for 0% there will be 30cm3 of sediment and 30cm3 of material generally in the sediment barrel but for 5% cementation there will be 30 cm3 of sediment and 1.5 cm3 of cement meaning 31.5 cm3 of material) although these are small amounts it is still significant especially if my experiment was repeated on a larger scale. This last point is a major fundamental flaw in my experiment, however below I have detailed some possible methods of minimising these problems; ? To make sure cement distribution is even I would use a mechanical mixer which would mix the sediment-cement mix for a long period of time to attempt to ensure even distribution. ? It would be possible using a light microscope and a thin section of a sedimentary rock to work out the percentage of cementation by measuring and counting this information could then be used to work out accurate % of cement. A simpler method however would be to use cores of real sedimentary rock with a known % of cementation. ? If the cement was left for a longer time period to cool, especially in colder conditions, it would be fully set (minimising dissolution in the water) and have less fractures as it would be setting for a longer period of time so it would contract less. Investigation evaluation and conclusion After completing my investigation I feel that I have answered and supported some of the original questions and ideas I had. However I have also discovered that the methods I chose were far to basic for accurate results, which could lead to calculations as to the Darcy level of materials etc. this means that my experiment is somewhat limited in its success as it has proved hard to back up my personal conclusions with conclusive data. It would be very hard for me to repeat the experiments with the modifications I suggested due to limitations of equipment and time, and even with these modifications I still feel that the experiments would not be an accurate indication of porosity and permeability as they are all taking place with small rocks samples that are out of situ. This is the primary problem with my experiment and my investigation as a whole as it is all being carried out in a laboratory away from the rocks natural environment. If possible I think the best method of assessing rocks porosity and permeability would be to use radioactive tracers in geological liquids and chart their movement through rocks in situ. This would be an accurate, if potentially costly, method of assessing rocks properties as reservoir and impermeable rocks. Overall I feel that my results did support my hypothesis, particle in experiment 3, but I feel my methods featured to many fundamental problems for my investigation to be a complete success.

Porosity and Permeability 9 of 10 on the basis of 2395 Review.