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Acidizing Summary, Dr. Ahmed Gomaa

lecture 1

Here’s a summary of acid stimulation in oil wells based on various sources:

Purpose of Acid Stimulation: Acid stimulation is primarily used to enhance oil flow by dissolving rock formations that impede it, improving well productivity significantly. This is essential in both carbonate and sandstone formations.
Types of Acid Treatments: The two main acid stimulation techniques are matrix acidizing and acid fracturing. Matrix acidizing injects acid at pressures below fracturing levels to dissolve rock near the wellbore, while acid fracturing creates fractures that enable deeper acid penetration into the reservoir.
Chemical Process: Hydrochloric acid (HCl) and other acids are typically used to dissolve minerals and improve permeability. In carbonate formations, acidizing often results in wormholes that enhance flow pathways, while in sandstone, a mix of HF (hydrofluoric) and HCl is common.
Stages of Acid Treatment: Acid stimulation often follows a sequence, starting with acid pre-flush to clear debris, main acid treatment to dissolve the rock, and post-flush to push the acid into deeper rock layers, ensuring maximum effect.
Safety and Environmental Considerations: Due to the highly reactive nature of acids, acidizing requires careful handling, strict safety measures, and environmental safeguards to prevent contamination and manage risks effectively.

transcript

(00:00) hello everyone uh this is me ahmad al-gharhi and i will be motivating this special session uh today we have very special guest speaker dr ahmad gomez now he is working for the bp in houston also before he worked for saudi aramco and worked for a long time for baker hughes dr gomer got his phd from texas a m university also he published many conference papers and many journals and also he holds many u.
(00:37) s patents so please if you have any questions you can leave it in the chat box and you know also at the end we will have few minutes to ask questions so you can keep your question to the end or you can write it down in the chat box dr gomez the mic is yours good morning all uh thanks ahmed for your nice introduction and please for the audience like i know stuff to have like uh online session or landing however i usually like to be interrupted i would like to get a question during the presentation so if you have any
(01:17) question any comment please use uh the messaging s ystem so you can you can drop us a message and dr rahman will help us to to read it and i cannot see i cannot see it from my side but the rahmah can help moderating and have let's try to be interactive as much as we can if we can be able to do that uh so to go through uh the title of the presentation today we will try to to give like a quick introduction about acid stimulation and usually i would like to start with a definition what does that stimulation mean
(01:58) by definition as a simulatio n mean it it's a process that's unsteady state non-isothermal 3d flow in porous media with the chemical reaction need to dissolve the rock so answer this rsd state flow so we are injecting and the velocity and the pressure actually changing with time they are not constant with time as you are injecting both our pores are changing in each minute as you keep injecting your acid non-isothermal at the acid reaction with the formation it actually sometimes reduce temperature so we may have temperatur e increase during (02:40) the reaction cd4 3d flow were not any more linear flow or not anymore radial flow were actually much closer to a spherical flow with the acid depending on the ratio between the vertical horizontal permeability will flow in in all the direction and the most important we are injecting the acid inside the formation so we will have a porous medium flow so we are governed by darcillo and as i've talked about acidizing we are talking about chemical reactions so the acid will actually dissolve the rook and that will result in
(03:21) variation in prostate and permeability at the acid reaction with the rock and you will have dissolving some rock so expecting increasing the porosity that will lead to increasing the permeability however as any reaction happening you will have also an action product and the reaction product sometimes will be completely soluble and then other actions will not be soluble so we'll have some precipitation of the reaction product this is will also inc reduce the porosity and will affect the permeability so we all
(03:57) the time during the acid dieting will have both including the prostate and permeability and the same time reducing the prostate and the permeability hopefully at the end of the job we would like to be sure that we dissolve much more than what we present leading to a much higher permeability and much higher production and that's will at the end our aims from any acidizing as enhancing world productivity will have to be sure that the world will produce a much better uh rates comparing before the authorizing second
(04:34) if we have any skill we need to do completely so obliged and dissolve this skill that's here the skin factor which is a more important for us we would like to reduce the skin factor especially in the near world bore area that coming from the damage so this is like a quick definition of that stimulation and a question is also like as a young engineer when you go to a company like your manage r will come to you and ask if we have a well when we will consider an asset treatment at what condition that you will start thinking that i need
(05:11) an acid treatment for my well we have only one answer for this question you use acid treatment when you have damage we do not use acid treatment just to increase the production as it is help to increase the production if you have a damage but if you do not have a damage acid will not will will not actually give you that much improvement of produ ction except if you are doing something else well other than the acid part but acidizing is always used when you have a damage and the way that you know that you have a damage is just simple definition you
(05:54) have unusual or unexpected reduction in oil production this is can happening like as a gradual you can see slightly you are losing your production not the way that there is a foreign engineer expecting or the model that can give you and that can give you evidence that you are building scale with time so you have a slow reduction in the oil and oil production or you have suddenly lose your production something happened like pretty quickly and that's happening when you block something you block the perforation of
(06:30) blood part of the tubing that can happen that you lose the production suddenly and one of the most important evidence you are looking to the gaza rush or the water cut if you start seeing unexpected increasing the gas or ratio of the water cut that's all can gi umping the acid at a pressure and injection rate less than fracture pressure so in our case we are pumping the acid inside the matrix without any intention of breaking this formation or creating a frag just pressure and rate low enough to just push the acid through the boras media and what would
(07:53) be happened as it would react with the boards and the natural fracture that exists however it will not create additional frag it just will dissolve the pores and improve your protein permeability category is a an organic acid and in organic acid we have two main type of acid we have hydrochloric acid we call it hcl and hydrofluoric acids and hf just to highlight hcl uh is a one that is mainly used like a lot majority of hazardizing somehow contain hcl it has a capability of dissolving a lot of mineral carbonate oxidized and a lot of things the other type is the hf and the hf acid is the only acid that
(09:58) dissolves under stone formation therefore when we are talking about sundistant
(11:24) frame height or 400 fahrenheit in this case the regular acid hcl hf is is a little bit hard to use them corrosion rate will be will be high so we are looking for some of the special acid at a special condition or when we can hcl is for a certain regulation is not acceptable so we can use the msa as alternate to the hcl any question so far okay so now you can go ahead and you know if there's any question i will stop you and ask okay perfect okay so let's go one by one invest it and let's t therefore it's a one of the assets that we typically use in the oil and gas industry and most
(13:53) important part direction product when it reacts with the formation whatever came out of the reaction product is completely water soluble so we don't see a lot of damage due to the reaction product coming for hcl and i have here the two reaction for two formation the first equation when hcl reacts with the calcium carbonate which is the carbonite formation you can see the reaction product is ca it's completely consumed does anyone can give any idea just i would like to to see like what's your thoughts about that the flowback ph 7bh that's neutral for team ph that's alkaline just to remind the
(15:56) people the ph numbers so we start with oxidizing was here with zero ph and water neutral is a ph of seven and if alkaline is a ph of 14 so if we start us valuing with a bh here what's what's the expected ph of the return fluid will be does anyone can guess it will be closer to the water wh ation it also correct with your vibe system and can corrode your vibe system and the casing and the tubing that you are injecting with and that can affect the integrity of this tubing therefore we need to use with a lot of additives like corrosion inhibitor to be sure it will not negatively affecting the integrity of the willpower the second part
(18:25) is the reaction rate each cell is very fast react reaction i wish i can be able to show to you but if you put a little bit of hcl with the calc some sort of iron control agent or some some sort of a clay inhibitor to be sure any sensitive clay inside the formation will not be effective affected by the hcl and can cause you swelling or fine generation and that is the cheap but as you can see right now we need to have a lot of additives with acids that make the package sometimes a little bit expensive if you have a clay if you have a sludge and if you'd like to have a high control
(20:23) control reactivity or control reaction rate so we d still high amount is not as high the hcl with calcium carbonate when we are talking about almost 1.7 for the carbonate case but still like 0.217 is still high amount of silica to be dissolved and that is the only acid system that can dissolve silicate that therefore when we talk about some responsibilizing hf it needs to come to your mind because that's the only essence that we can use dr gama i i received a question uh what if we use only hf and not a mixture of hf plus hcl what would happen second precipitation you will have a sodium pholosilicate or potassium full circuit and this
(23:59) part is actually well presented sorry for the issue of the hf is the reaction product will have a lot of precipitation however this precipitation doesn't happen immediately it happened at bh when the bhs starts four to six the reason of using the hcl is hcl will not react with any of these it will not react with a silica it would not react without tonight it would not react with any sodium clay o the advantage is we have a lower corrosion rate it does not react as much with uh with the tubes so it does not reduce the integrity of the tube also we can easily inhibit them we can
(26:18) add slightly of corrosion inhibitor and we can use them in high temperature organic acid being used extensively between 250 from height up to 350 fahrenheit without any ratio again if we have a high we use them when we have a high acid by point of time and that's happened because like sometimes you cannot ny so if you like to select between schlumberger for example or bakery use or halliburton your selection will be depend on what additive each company can provide to you the costs and the performance of each chemicals for example all the three all the surface company in the market can easily provide use hcl and hf
(28:29) it's commodity product so you can actually even the production some of the production company can actually buy them directly however the main distinguish between the surface com you have and the value need to be less than 0.05 bound per feet do you know you can see like how much thickness you are losing from the tubing for this amount can anyone guess how much sickness of the tubing lost by 0.
(30:17) 05 pound per square feet how much thickness at the end of the treatment but does anyone see anything no okay so it's like the way by the way they can answer because this is a zoom meeting so if they have answers you can speak so do oh okay so 31 micron actually that is the o be sure the corrosion inhibitor will work in a more effective way iron cleating agent iron is one of the things that can actually cause a lot of damage inside the formation so we'd like to be sure this iron will not be precipitated and be been in solution so we use an additives called iron control agent to keep the iron in solution
(32:34) other additives and dislodge agent and it being used when you have an oil well and the oil that you have have a lot of asphaltene to be sure this asphaltene matter exercising itself sandstone or carbonate and the last one is acid fracturing so we will go one by one and see which each what what does each treatment do and what's the typical asset that we use for each treatment first one is called bickling treatment and usually we do this before any acid job is the process is pretty simple we are circulating usually a low acid strength between three to five weight percent hcl and the idea here we try to remove any
(34:53) iron or any rust in the pipe ntrol agent
(36:04) a second treatment which has a different name some people call talking some people call agitating some people call acid watching and the idea here or the the process here is pretty simple we like to put some acid inside the wellbore and we soak it for some time to remove any scale inside the tubing and dimensions can see the picture or not can you see this one this is the amount of scale that being deposited was time so as you are producing calcium carbonate one of the major ion so you are having a sludge issue you will have and slowly agent if you need some solvent you will add some solvent if you need iron control agent you will
(37:57) add iron control agent depending on what the formation that you will have other treatment called acid breakdown job and in this case you are merely trying to affect the perforation usually when you have a new well and you are perforated with a perforated gun there will always be a debris inside the buffer inside the perfection tunn to the one that will cleaned later after that we can move on to the major uh acid treatment here the first major one is the sandstone as diving and as we just said earlier the presentation the amino that have been used in to dissolve in sandstone is hfacit system and as we are talking about ascendant
(40:03) solar diesing so still talking about matter exercising so we are injecting the acid as the pressure at the pressure or at the rate less than the fracture pressure and you can see here i have ill be dissolved by the hf so initially we'll bump hcl just to dissolve any carbonate that that that if it's existed when the hfc it it can accuse damage then we'll go with the main acid which is hclhf treatment and acid will work to toward the silica and dissolve the silica behind it at the later stage we'll do overflows with hcl and the idea here is to keep the ph as low as possible so you don't have you cannot reach to
(42:17) the bh425 and you don't have any precipitate when you talk about t s the carbonate of the diving and and in this one is a little bit different than the sun sun is diving in this case we are actually creating our mole the reason that we are creating the or more because the acids that we are using will have a much hard solving power if if you just remember like hcl who attract with carbonate it one gallon will dissolve 1.
(44:21) 7 pound so and would love it that fast therefore when it reacts it actually will create the channels inside the formation because of th e however if you start increasing the acid rate more and more you start getting what we call dominant wormhole when it's a long vibe inside the formation so as you're injecting here with a high rate you can see the wormhole is going pretty deep usually you can see still inlet is a little bit small bigger than the parenthesizer frame until you reach what we called dominant wormhole or optimum optimum hole usually will see almost has a constant diameter through the section and it will take the min acturing and here we are bumping the acid at higher pressure more than the more than fracture
(47:44) pressure so what will be happened we will create an actual track so if you bump it you'll you'll see like i have here like this is the sort of the flag that being created with the asset you are not in a more bombing acid in another direction what's happening as soon as you create the frac all the acid will go toward the fracture what the acid will do the acid will start to react with the fractur dant inhibitor is actually creating a layer in the tubing okay let me have it as a go back a little bit okay maybe i will delete this one okay so corrosion editor if you have your tubing here usually corrosion inhibitor create a
(50:15) layer at the as a tube a protection layer on the tube this layer eliminate the acid to the views on the surface of the tube and protect it that is the corrosion inhibitor how would do exactly is actually increase the viscosity of the acid itself make it a little ivity that you will have is much less so in the asset fracture you would like to be able to to be sure that you will have enough acid distribution to create a good itching without
(52:39) bumping less acid to have a very minimal itching or bumping too much acid that can actually resolve everything and when you close you will not have this on uniform pattern good so the best way to do the asset fracturing we do it in a three different step the first one we bump across link it back and to create t acid bliss mint which is happening how can this be able to be distributed the acid through our bore so as it is known as a reactive fluid and as it's bombing inside the formation it will increase the permeability of the formation so imagine if i'm having a world board
(54:44) like having this cartoon and i'm actually bumping acid as like any fluid it will go first to the hyper mobility formation so imagine i'm having here three type of layer like real really high permeability one medium permeabi ne right now so the placement technique that we have we have either mechanical or chemical technique mechanical is example we have called tubing backup project blood and or chemical techniques we have formed acid the emulsified acid gel acid and insert usual doesn't just go one by one like mechanical we have called tubing and in this case we're actually using a
(56:38) coal tubing to spot the acid at each location so in this case you are guaranteed that your each zone take thick acid so you are p something from the surface that can actually block each perforation we call it both healers this mechanical method is actually is the best method to be sure that we have a good distribution it's all of it you can be sure that when you use whom you are using mechanical you are pretty sure that you have a good balance with and you you are 100 sure that has been evenly distributed or distributed in the way that you like to have however it usually need cement certain type of completion you
(58:49) till a part of the mechanical it work only if you have a perforated well you
(1:00:05) need to have a perforated casing and cement it also need a high bombing rate if you are bombing at a low rate it will not work and designing how many balls you need to run is is a little bit like critical and no not all the time is being designed right and you may actually blog affirmation that you need actually to treat it so it's still a little bit tough to deal therefore we like to to use the chemical metho nd based on surfactant and the volume r1 is is not used as as well but however the most recent one is a surfactant and been used extensively in the field currently some people call themselves diverting acid or viscosity
(1:02:04) control asset but in the same name or the same behavior so the idea here is working with the ph at a low bh the acid will have a low viscosity and when the bh is reaching around two the actually the polymer will be cross-linked and initiated a really high viscosity and ow back and you treated the whole section without any issues actually that was my last slide today so please let me know if you have any questions guys please if you if you have any question you can go ahead and ask any question before we finish okay dr ahmad thank you very much for the informative session and for sure we we wish to have
(1:04:09) you again in the future thank you

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Q & A

what is Stimulation?

the definition of stimulation means that it is a process that is unsteady state, non-isothermal, 3-D flow in porous media with chemical reactions needed to dissolve the rock we are injecting and the velocity and the pressure actually changes with time beside changing in temperature also.
the reaction 3d flow were not any more linear flow or not anymore radial flow were actually much closer to a spherical flow with the acid depending on the ratio between the vertical horizontal permeability
we are injecting inside the formation then we have reducing in the velocity medium flow so we are expecting to increase in both porosity and permeability sometimes we have soluble products and sometimes we don't have soluble products
at end of any acidizing we aim to enhance well productivity and much better rate comparing before acidizing we need to reduce the skin factor especially if the near well pore area that coming from the damage

when the acid treatment needed?

when you have a damage; we are not using acid treatment to increase the production, it will help if you have a damage only, and the way that you know that you have a damage is just simple definition you have unusual or unexpected reduction in oil production, this is can happening like as gradual reduction or suddenly reduction because of something happen to the well (blug, block perforation) and you can look to gas oil ratio, if gas oil ratio increased that is an evidence that you have some sort of damage in the formation.

A1.