Report On Drilling Labs
Experiment 1 (Drilling Fluid Mud Density)
Definition: The drilling fluid term refers to the technic used for facilitation of drilling boreholes, and to improve all necessary functions needed for a fine drilling.
(The weight of Mud *0.052)= Gradient of Mud in psi/ft.
(The weight of Mud in lb/ft3)/144=mud gradient in psi/ft.
(Mud gradient) 8.3*0.052 =0.432 psi/ft.
(Mud gradient) 64/144 =0.044 psi/ft.
Mud sample No1:
(Mud gradient) 9.13*0.052=0.475 psi/ft.
(Mud gradient) 69/144=0.480 psi/ft.
Mud sample 2:
(Mud gradient) 10*.052=0.520 psi/ft.
(Mud gradient) 76/144=0.530 psi/ft.
Calculation: For calculation of the Density and Mud gradient, the following formulas were used.
Density= (lb/gal)/ 8.345.
Mud gradient= (lb/gal)/ 19.24.
Volume and mass
Fresh Water: 8.3/8.345 = 1.0 (S.G)
Mud sample1: 9.13/8.345=1.1 (S.G)
Mud sample 2: 10/8.345=1.20 (S.G)
During the experiment, water and two different types of mud were used. In addition, the densities and mud gradient of all three samples were separately calculated. According to the results, the mud sample number 2 has the highest mud gradient and density, which is related to the materials used in it, plus the water, which had the lowest amount. As it’s known that the density of the mud has a direct effect on the hydrostatic pressure in the wellbore. Therefore, as there is an increase in density of mud, there is an increase in mass of mud, also HP increases in result of increase of the mass, which allows the control of oil production rate. Bentonite, Xanthan, Salt, and Barite were the additives used in the samples.
Bentonite: It helps with blowout prevention and cooling the cutting tools.
Xanthan gum: Added to increase the viscosity of the mud and to maximize the drilling bit rotating.
Salt: A polymeric agent added for losing the liquid, which increases the yield strength.
Barite: Used for increasing the density of the mud, which in result increases HP and a better control of the formation pressure.
As mentioned before, water and different types of mud were used in this experiment, in order to test their mud gradient and density, and as it’s shown in the calculations and results sections, as the density of the mud increases, the mud gradient also increases.
Experiment 1 part 2 (fluid viscosity)
The difference in viscosity of the samples is related to the molecular attraction force of the liquid’s molecules, therefore, the greater are the adhesion and cohesion forces, the higher is viscosity.
Basically, the mud viscosity mainly affects the drilling cutting. To be more specific, a mud with high viscosity facilitates the collection of the cutting, and from the other side using a low viscosity mud will reduces the ability to remove the cuttings as they are heavier than the mud.
In general, three different samples were tested to check the difference in their viscosities, and according to the time measurements, water in comparison to the other two samples has the lowest viscosity, and sample number two has the highest viscosity. Therefore, it means that water is not a proper choice for injection in the well, due to the fact that it cannot lift the drilling cuttings.
Experiment 2 (Retort Analysis)
Oil/water ratio: In Mud Sample 2 (OBM)
Water Volume = (21/72)*100=29.2%
Oil volume = (51/72)*100=70.1%
Water/Oil ratio =41.7%
The additives have two types, active and inert. Active additives are used to increase the viscosity and strength of the gel, though; inert additives are used to increase the weight (Density) of the mud. For example, clay, bentonite, and polymers are active additives, and calcium carbonate and barite are inert additives.
Liquid volume is 9.7cc (97%)
Water volume is 9.7cc (97%)
Solid volume is 0.3cc (3%)
Experiment 3: Drilling Fluid (mud) Rheology
Sample two at 20.5oC
Sample 1 at 20oC
Sample 2 at 50oC
Plastic Viscosity (PV), cp = 600 rpm reading-300 rpm reading.
Yield Point (YP), lb/100ft2=300 reading rpm – Plastic Viscosity (PV).
Apparent Viscosity (AV), cp 600-rpm reading/2.
(PV) 21-13= 8cp.
(YP) 13-8= 5 lb/100ft2
(AV) 21/2= 10.5cp.
Gel strength =3 lb/100ft2
Reading the distortion of the fluid is called rheology, and its importance in many analytical aspects is accepted. For example, the analysis of annular hole cleaning, fluid viscosity, fluid flow velocity, and pressure friction losses can be mentioned. Moreover, there are several rheological models, such as Newtonian, Power-law behaviour, Bingham plastic and Robertson-Stiff model.
Newtonian Viscosity fluids are those defined by a single term, usually contain water and light oil, and always the shear stress of these fluids is related to the shear rate, in a linear manner.
A fluid that the reduction of its viscosity increases the shear rate.
When a fluid can be either Newtonian or non- Newtonian, and the flow of it is reliant on both shear rate and shear stress, its Bingham plastic.
This rheological modelling has two types. The first one provides a much more exact rheological data, though the second type provides a clear image of the relations between the velocity fields, which depends on the relation between both pressure drop and shear rate. However, certain liquids under the influence of stress and over a certain period behave in a much more predictable manner. As an example for such liquids, the Rheopectic liquids can be mentioned, which under stress and over a certain period increase in thickness/viscosity.
On the other hand, the Thixotropic liquids show an opposite reaction as stress over a certain period causes a decrease in viscosity. The additive can affect the rheological behaviour in so many ways, for example, addition of PEG causes a more jelly or muddier substance, which is the result of the interactions between all additives, and thus a gel like substance is created.
Also as an example, the rheological substances depending on being oil-based or water-based substances can be mentioned, it’s clear that the overall effect of each type on rheological behaviour of the samples is completely different.
In general it must be noticed that there are so many laws that must be taken into consideration during rheological studies of the intricate and complex mud samples. Different fluids under a specific stress can act and react in different ways, and the effect of different additive substances used cannot be ignored, as different additives have different effects on different types of fluids that are going to be used to maximize the efficiency of a project. According to the samples given below, the slightest changes in temperature can cause what a major effect on the viscosity and amount of used. For sure, temperature plays an important role rheology of the mud as it can be considered as a form of stress. The slightest changes in temperature can cause slight changes in results, and drastic changes of the temperature will lead to much more drastic changes in the overall results.
Experiment 4 API Filtration Test: Standard Filter Press
Spurt loss equals to volume at t=zero in result mud sample 1 equals to 0.89cc and mud sample 2 equals to 0.059cc.
Standard API filter loss is equal to volume at t=30 which equals to 1.59*sqr30+0.89=9.6cc for mud sample 1 and for mud sample 2 the result is 21.5cc.
Report thickness of filter cake equals to 1.5mm for mud sample2 and for mud sample1, the thickness equals 1mm.
The thickness of mud sample 2 is 0.059inch and mud sample 1 is 0.039 inch. The mud sample 2 is greater than 1/32. The first sample is close to 1/32.
The express thickness of filter cake per unite area equals to pie*r2 =pie*1.52=7.07inch.
Therefore, mud sample 1 = .039/7.07= 0.006 inch and mud sample 2 = .059/7.07=0 .008 inch.
Mud sample 1 has a flexible soft shiny surface, as mud sample 2 has a dry, firm and brittle look.
In the beginning, a stuck pipe is considered, and by “stuck”, we mean unable to be removed from a hole without being damaged. Moreover, a pipe is considered stuck if the pipe can be removed without surpassing the maximum allowed hook load of the drilling rigs. The sticking of the pipe can be classified in two major categories, which is irrelevant to this discussion.
However, a thick mud cake also can cause a pipe to be stuck, therefore according to one or both requirements to be classified and considered as “stuck”, which leads to weakness of bore stability due to presence of a thick mud cake layer on the pipe, which is stuck.
Bore stability may be also referred to differential pressure and mechanical stuck pipe.
The mud samples 1 and 2 at 30 min are:
Mud sample 1: The Standard API filter loss equals to 0.89cc.
Mud sample 2: The Standard API filter loss equals to 0.059cc.
Physical properties of mud cake for sample 1: Flexible, soft, and shiny.
Physical properties of mud cake for sample 2: Brittle dry, and firm.
It is known that starch is the best additive to improve control of reduced mud filtration volume, specifically in low temperature wells and in result of high biodegradability.
Experiment 5: API HTHP Filtration Test: Standard 157 ma HPHT filter press
T= 100 0C Pressure= 500 psi plus minus 5 psi
Mud sample: 20% water 50% oil 30% solids it was (oil-based mud)
The properties of the mud: Jelly-like, shiny, and flexible.
Filter paper thickness and diameter 0.2 mm, and the diameter is 2.25 inches.
This experiment tests a sample that has been under differential pressure, to be exact 500 Psi. The maximum pressure breakdown was 600 Psi, and a minimum set in amount of 100 Psi (600 psi – 100 psi=500psi).
It analyses the space, which is designed for compression of any vapour formed in result of high temperature to collect liquid filtrate.
The analysis is that space is created for compressing any vapour that may have formed as a result of high temperature conditions in order to collect liquid filtrate.
It must be noticed that here water is not an applicable as it is not a preferable drilling fluid under high temperatures, as in high temperature the water is easily vaporized.
After 30 minutes, the volume of the filtrate equals to 0.5 cc that means the standard filtrate volume is 1.0cc in 30 minutes. Also, the area of the standard API paper filter is twice more in comparison with paper filter used in this experiment. Thus, the accepted value must be multiplied by two.
At the first step, the filtrate must be gathered and then the residual mud cake after a slight rinsing will be ready to be examined and analysed. Its physical properties are being soft, flexible, sticky, and jelly-like in general. The mud cake formed in HPHT has the minimum thickness in comparison to the thickness of the mud cake formed in LPLT test, and that’s due to the excessive pressure, that compress and make the mud cake to have a lower thickness. As it is shown in the results section in above, the weight of the samples is calculated in different units. It must be taken into consideration that because of the SCT (Static condition test), the viscosity of the filter cake does not essentially reflect the actual down-hole condition.
Under the HPHT formation, the oil-based drilling fluids are a good choice, as they do not cause any damages to the hydrocarbon-bearing zones. Thus, it remains the natural position around the well bore.
Therefore, it maintains the natural circumstances of the area around the well bore.
The filtrates of the water-based mud after entering the formation reduces the natural permeability of the formation.
API LPLT Standard Filtrate per thirty minutes:
· Sample 1 = 0.89cc
· Sample 2 = 0.059cc
API HPHT standard Filtrate per thirty minutes:
· Sample 1 = 1.0cc
It is important to remember that the thickness of the filter cake cannot be an accurate indication of down-hole as it is SCT (static condition test), and due to the fact that the circulation of the mud in down-hole which is an important factor cannot be simulated.
Therefore, it is highly advised to perform an experiment to analyse the changes of density caused by the mud cake, in both terms of formation and filtration.
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