transcript

"(00:05) hi I'm Kyle Travis I'm a petroleum engineer and an instructor for petrol skills I'm here today to talk to you about completions and work overs completions and work overs as one week class taught by petrol skills and it's very well received in the industry today I'm going to talk to you about acid ization and of course completions of course stimulations are a big part of completions and acid jobs are a big part of that so let's get into the presentation so these are a nice list of all our (00:48) completion methodologies sometimes we under in wells will intentional create cavities in our formations even explosives have been tried not very effectively matrix acid izing very effective particularly in carbonates but also used in sand stones and that's what we'll be talking about here in a little bit solvents prop hydraulic fracturing of course we frack a good many of our wells most of our wells in the North America now onshore we also acid frack our wells and occasionally pump chemical surfactant flushes to remove problems (01:30) like water blocks and such all right if we're performing in a matrix acid job we've got to keep our injection pressure below the frack parting pressure for the rock it's absolutely imperative normally our target formations for matrix acid jobs are higher perm reservoirs we say greater than 40 mil at our C's but that's plus or minus carbonates in general are much simpler to clean up than sand stones but we do perform matrix acid jobs in both one of the things to be careful about with matrix (02:08) acid jobs is using too much acid or too strong an acid if we pump too much acid we can dissolve the cement material in our formation and actually weaken it in carbonates that can lead to plastic flow or collapse casing in sand stones it can lead to sand production and collapse casing as well so very detrimental if we pump too much acid other types of acid jobs besides matrix jobs include acid washes where we pump acid and try to remove things like scale deposits acid soak acid soaks aren't used too much but (02:52) sometimes we perforate in acidic acid and perform a over-pressured slow soak into the new perforations to clean up the perforations acid fracking is limited to carbonate formations only in which case we are trying to create a stimulation and lower perm rock and carbonates we've got different types of acids that we use in the oilfield we've got mineral acids like hydrochloric and hydrofluoric acid which are very strong acids react very quickly we also use organic acids in our stimulations organic acids do not react (03:35) as quickly as the mineral acids and therefore have properties that make them very beneficial to use in higher temperature wells and then hybrid acids hybrid acids are combination of the two both the organic and the mineral acids and we get the beneficial properties of both and sometimes we use acids where we intentionally slow down the rate of reaction so that the the unspent acid can get out further into the formation before it reacts and then occasionally we use some solid acids but we don't use those very often well every (04:15) acid has a disassociation constant and that disassociation constant is an indicator of how fast that acid will react and if you we've got acidic formic and hydrochloric acid here and you can see that the hydrochloric acid has a disassociation content several orders of magnitude higher than formic and acidic acids and indicate that it will react much faster and it is or absolves more rock than will the formic and acidic acid as well so looking at our mineral acids again that's hydrochloric and hydrofluoric acid hydrofluoric acid is (04:54) used the most in the oilfield typical concentrations go from seven and a half to fifteen percent but we can actually go as high as 28% concentrations hydrofluoric acid HF acid as normally per pumped at low concentration somewhere between 1 and 3% HF and it's always pumped in combination with either hydrochloric acids or one of the organic acids and those are normally pumped at concentrations of 6 to 12 percent and we'll talk about why we pump those together again generally speaking these mineral acids are very powerful acids (05:36) they react very quickly and there are certainly HSC concerns with them if these acids were to get on your skin they could burn a hole in your skin and we have to be careful about that ok this is this slide is addressing the strength of concentration of acid because someone would undoubtedly say well why don't we always use 28% well the stronger acid is not always the best acid as I said in one of the early slides sometimes if we pump too strong acid or too much acid will weaken the rock if we dissolve the cementing (06:14) material will weaken the the rock and actually hurt our well but standard concentrations for HCl are 8 15 and 28 with the most common 8 and 15% the acid reaction in carbonate reservoirs and bicarbonate reservoirs of course we're talking about limestone and olamide's it will dissolve the rock matrix completely and that's very favorable but if we have calcite cement present in our sand stones and we pump hydrochloric acid it will dissolve that cementing material weaken the formation and again lead to (06:56) sand production and possible big-time problems the reaction with hydrochloric acid and calcium carbonate is complete once the Arak the reaction completes then all that's left is calcium chloride water both liquids and co2 gas when we pump matrix acid jobs particularly in lime stones lime stones have a high degree of heterogeneity and they oftentimes have very permeable streaks that one run through them so when we pump acid into those high perm streaks they start eating away the formation and creating these holes and the more acid that's (07:37) pumped the rounder they get and we call them wormholes because they're fairly erratic very similar to what an earth one worm digs in the ground so these worm holes can create highly permeable pass back to the wellbore but if we keep pumping acid through there we'll just keep Sri stimulating the same rock so sometimes we want to divert the flow of that acid and we might do that mechanically with with ball sealers or we might do it with viscosity and gel the acid to cause more diversion and a more uniform dispersion of the acid we (08:14) pump hydrofluoric acid in our sand stones okay and so we call these treatments on sand stones mud acids that's because they were developed to solve the problem with the the damage that was being created by the bentonite back in the the 40s when we were damaging our wells with bad drilling practices we had a lot of mud damage and so they developed the mud acid to dissolve the bentonite and clean that up well HF hydrofluoric acid will react with calcium chloride excuse me with calcium carbonate with clay material (08:56) with silicate which is what our sand grains are made of and some of these reactions are positive some of them are detrimental particularly the reaction with calcium carbonate when HF acid that's hydrofluoric acid reacts with calcium carbonate it produces a damaging precipitate and so we would like to avoid that reaction from occurring the concentration of acids that we pump in these mud acid jobs can vary the hydrofluoric concentration normally fluctuates between 1 and 3% and then the hydrochloric constant (09:37) in somewhere between six and twelve percent which particular percentages we use is a function of the clay content in the rock this is all we have planned to present today regarding acid izing in this section we cover the organic acids as well we talked about acid fracking and this is part of this stimulation section and of course in the stimulate let stimulation section we also talked about fracking I hope you enjoyed this and will join us for the next section which will cover unconventional wells"