 Welcome to this 17th lecture which is on well completion. So the topics covered in this lecture, well completion followed by well development, followed by well protection, then it moves on to well rehabilitation and lastly well testing for yield. So now we will start with the first topic of this lecture that is on well completion. So this well completion it is the process in which basically a permanent nature of the well is established. Whenever a well is dug, so it is we are disturbing the land profile by drilling a well and then once this land profile is disturbed so that we get we can harness ground water, we can extract ground water. So then what happens is, so there is a possibility that there is either erosion or undesirable erosion or sedimentation of all different sizes of soil particles. So it can range from the smallest clay to even boulders, even it may not go up to boulders but definitely it can go up to gravel or so therefore there is a need to maintain this balance and that is precisely done in this well completion. So basically so well completion is the process ensuring balanced sedimentation stroke erosion of the particles forming the geological strata in which the well is drilled. So this the word balanced sedimentation or erosion so this is very important. So this is to do that, so the processes involved in well completion are, so the first one is that is placement or cementing of well casing, so here this is and stroke or so this is a placement of well screen and so this is a placement of gravel packing or simply gravel packing. So these any or all of these three processes are involved in this well completion. So now let us briefly discuss what this well casing is or well screens are and what these gravel packings are and how do they help in this well completion process wherein a balanced sedimentation of erosion so that it attains a steady state and so that the geological formations will remain so that is ensured. First let us discuss about this that is the well casing. So here so this well casing so basically it is the to maintain so it is a lining to maintain an open hole from ground surface to the aquifer from the ground surface to the aquifer. So basically here what is done is some cover is provided so that so this is the opening the open hole from the ground surface because see the thing is unless the we ensure a continuous that is supply of ground water so well will not serve its purpose. So therefore so this well casing is very important wherein so this the porosity or rather the perforated nature of the ground is maintained so through which this infiltration takes place and so this when I talk of infiltration so it involves percolation which is generally in the vertically downward direction as well as seepage which is generally in the lateral direction. So therefore so this well casing essentially ensures that so the well gets the necessary the ground water storage into the aquifer so through which the well draws its water and here so there are this one that is so the this well casing so this is here you can say this is a types are so the first one is the surface casings and followed by so there is a pump chamber casing so these are all self-explanatory so here the surface casing is at the surface level and what it does is through the upper strata of unstable or fractured material so it is installed and then relatively into a stable and relatively impermeable material. So here so it serves various purpose such as the it supports unstable material during drilling reduces loss of drilling fluid facilitates installation of removal of casing aiding in packing placing a sanitary seal and lastly it serves as a reservoir for a gravel pack. So basically this is a surface casing so here you can say the purposes of surface casings which are installed at the surface level are let me write here a so let us say this is 1a that means 1 refers to surface casing and then a refers to the first purpose so this is supporting unstable material during drilling that is during well drilling and next it is the next purpose is reduction of the drilling fluid loss so this is also this purpose is also achieved by surface casings. The third one is the third purpose is facilitating the installation or removal of other casing so there may be some other casings so that is the either the installation or removal so that is facilitated and fourthly so it is helping in packing I am sorry placing sanitary seal so this is also one of the important purpose of surface casing and then lastly it is serving as a gravel pack reservoir that means whenever we need gravel pack so the surface casing will provide that from its storage so these are the purpose of surface casing and then so this is next coming to the pump chamber casing so here it consists of all casings above the screen in wells of uniform diameter so next this is so whereas this surface casing so they are at the this is at the surface level whereas pump chamber casing so these are at the so the or all the casing above the well screen having uniform diameter so here I am writing here having a uniform dia so this is pumped chamber casing whereas surface casing is at the surface level so this is regarding the placement of well casing and many times so this cementing is also required because simply placing a well casing is not good enough so it has to be held there so therefore for that cementing is required so for that we may use a cementing material such as the ordinary Portland cement or any other binding material so which will hold in position the well casing and then so next we will go to that is the well screens so here in the well screen so it is basically it is some kind of a this one perforation that is on the well it is between the lateral surface of the well and so through which only a limited this one that is a limited amount of soil particles will be allowed to so here so this so well screen it is a perforated cover placed on the ground water yielding surface surfaces or surface or surfaces of well so and here so this is so depending upon the formation and also the well casing also differs and of course the depending upon the well yield so the that is the say for example the well casing as well as a screen so the size of the sizes of well casings and screens and well screens the recommended minimum sizes of well casings well screens as per USBR United States Bureau of Reclamation so they are as follows so they are based on the well yield in meter cube per day and so nominal pump chamber casing dia so that is in centimeters and surface casing dia so that is also in centimeters for so this is for a b c so here this a refers to that is naturally developed wells b refers to gravel packed wells and c refers to I am sorry so this is only a and b and then the nominal screen diameter nominal pump chamber casing diameter and here let me also give so that is so here let me do it like this nominal diameter in centimeter of so here this is a for pump chamber case pump chamber casing and then well screen so essentially we have so this is our this is our first column that is the well yield in meters so the next column is the nominal diameter for pump chamber casing and nominal diameter for well screen and then followed by so this is the surface casing this let me call this a and then this as b so here so this is well yield so there are the various things are there so this is less than 270 then 270 to 680 and then 680 to 1900 and then 1900 to 4400 and I will not go beyond this and let us see although there are many more are given so let us say 4400 to 7600 and for this the nominal pump chamber so this is 15, 20, 25, 30 and then 35 in centimeters so that is the nominal diameter for pump chamber casing and then similarly nominal screen diameter is 5 for well screen that is 5, 10, 15, 20 and 25 and so here the surface casing so the the diameter that is a for naturally developed wells C is not there this is a for naturally developed wells so that is 25, 30, 35, 40, 45 and then similarly so here it is for gravel packed wells so this is 45, 50, 55, 60, 65 so this is taken from the US Bureau of Reclamation and of course the same this 5 centimeter gap so that goes on so the next level is so here let I can represent the various sizes of well yield so this is well yield so that is in meter cube per day so here let me represent this one after 7600 next is 14000 next is 19000 next is 27000 so that means so from 7600 to 14000 so this everything gets increased by 5 centimeters so it is 40, 45, 50 and similarly here it will be 30, 35, 40 and similarly here it is 50, 55, 60 and similarly here it is 50, 60, 70 only in this case whereas in this case there is a 65, 70, 80, 90 so like that so these are this one and now we will move on to that is so there is also an equation that is given for the so that is optimum entrance velocity of water through a well screen water that means obviously this is ground water so this has been so done by so this has been proposed by Walton and Walton in the year 1962 so that is so the hydraulic conductivity in or rather aquifer hydraulic conductivity in meter per day versus the optimum screen entrance optimum screen entrance velocity for ground water so that is in meter per minute so here this is 250 then 250, 200, 160 after every 3 rows I am going to write a horizontal line 160, 120, 100 next it is 80, 60, 80, 60, 40 and 20 and then less than 20 so the optimum screen entrance velocity so this is 3.7 this is all in meter per minute 3.4 then 3, 2.7, 2.4, 2.1, 1.8, 1.5, 1.2, 0.9 and then 0.6 and here for this there is a formula that is let me write the formula here this is vs is equal to q divided by c pi ds c pi ds ls multiplied by p so this is vs is the so this is the optimum screen entrance velocity for ground water so which is denoted by vs and then q is obviously it is a discharge the well discharge and then the c is the clogging coefficient and so it is generally 0.5 and then so that is ds is the well screen dia and then this ls is the well screen length and then lastly this p is the percentage open area in screen percentage screen open area so basically so this is the formula based on this so this optimum screen entrance velocity is expressed by this formula that is q the well discharge divided by c the clogging coefficient and multiplied by pi multiplied by ds ls into p where p is the percentage screen open area and here so this is how the optimum entrance velocity once this optimum entrance velocity is ensured so then so we can expect that so that will be the well will function better so next we will discuss about this gravel packs so this gravel packs basically they serve as they consist of gravel and then they serve as a via media an intermediate media between the aquifer material as well as the well so wherein there is the hydraulic gradient and so this actually they will reduce the ground water velocity significantly and then so let me show a typical this one this is suppose this is the well and here so this is the ground level and here so this is the well shoe so this is the shoe just like our shoe which protects us against as one and in between so there is a here so the screen goes on till the impervious layer so here clay or other impervious layer and here so this is the typically once so here we can say this is the gravel pack around the here there is a so this is the well cap and here we can take this two ways one so this is the there is one more casing here let me show this and so let me so here so this is the so this is the shoe and then this is the gravel this is the gravel wall or gravel pack and here this is so here this is a temporary casing I am sorry so this is a temporary casing and then so here this is a working casing this is intermediate this is the working casing and so the red one so this is the protective casing so this is the I have just shown this with the red color and then followed by this black one so this is a gravel pipe so this is a gravel pipe which is 8 to 10 centimeter and then so this is a this is a temporary casing here which of course I have already shown so this is a 15 centimeter more grouted and then so this is the top soil and so this is a typical and this is a gravel pack a well a typical well with gravel pack so this is how so the well completion is done so that well attains a stable configuration so that there is a balanced erosion and sedimentation so next we will go to well development so that is the next topic of this lecture so essentially so this well development it is the process of increasing specific capacity increasing well specific capacity and let us recollect here so specific capacity is the discharge per unit drawdown that is a specific capacity and so additionally so this is prevent sanding that is accumulation of sand comma obtaining maximum economic benefit through the well for its extended service life so all these things firstly it is increasing the well specific capacity which is that means increasing the discharge per unit drawdown preventing the accumulation of sand because once the sand is accumulated so then it will the well discharge will reduce because and then next is obtaining the maximum economic benefit so that means quality water should be quality ground water should be extracted so over an extended service life of the well so all these things are involved in well development so the processes the common processes employed in well development are 1 pumping 2 it is surging 3 is surging with air and 4th is back washing again this is with air then followed by hydraulic jetting and use of appropriate chemicals hydraulic fracturing and lastly use of explosives so these are some of the processes which ensure that they can increase or if not maintain the initial level of specific capacity prevent accumulation of sand as well as obtain quality ground water for the extended life of a well and here say some of the typical this one here I would like to bring it to the notice that is so here this compressed air so basically as we all know so this air wash is very effective in removing the fine clogged particles and then so therefore we can ensure an increased we can maintain a high level of specific capacity or we can further increase the specific capacity and so therefore this so in this case the typically the air jet plays a very important role so in this case I will suppose this is a well and here we have so the suppose this is the so this is the well casing well casing and then here there is below that so there is a well screen I suppose this is and then so there is also there is an air pipe and this air pipe so this is a fine sand deposited into well so this is the air pipe here there is a so typically so this is the air jet and in this case so this is the discharge so water is taken out here and this air is here and then so there is a clamp here so let me use this so this is q and then so here so this air is an air jet is let in through the air pump and then so that what it does is it will simply blow the fine sand which is deposited and so this one so the well is so this is basically a well development through compressed air and of course the same thing can also be done there is why this back washing through air and of course the various kinds of chemicals or this hydraulic jetting so this is so in this hydraulic jetting I suppose so here suppose this is the screen material so here what is done is so this is a well development through hydraulic jetting so here a typically a hydraulic jet so what this does is a through this hydraulic jet so this the screen cloggings are removed in this case so the well is developed and so this is also one of the methods of first one so we will stop here and we will continue in the next lecture on this one although we had planned to complete this well protection well rehabilitation and testing of wells so for want of time and so this will be discussing this in the beginning of the next lecture and move on to the new chapter in the new module in the next lecture thank you.