CA1202737A - Use of magnetic separation in scavenging hydrogen sulfide - Google Patents

Abstract

USE OF MAGNETIC SEPARATION IN SCAVENGING HYDROGEN SULFIDE
Abstract Use of ferri-magnetic reactive iron oxide particles to react hydrogen sulfide in water, hydrocarbon liquids or drilling mud affords quick, effective scavenging of these liquids without accumulation of particulate matter and without wasting the reactive particles. The reaction product is environmentally safe, so that it may be disposed of on a simple waste heap.
A quantity of the magnetic iron oxide particles, principally a synthetic porous Fe3O4, is suspended in the liquid. The quantity added is in excess of that required for the reaction with the hydrogen sulfide in order to speed the reaction time and provide a large margin of safety.
In use, the reactive iron oxide particles contact and react the hydrogen sulfide, forming a non-magnetic particulate product of reaction. Thus, if used to scavenge a drilling mud, this contact and reaction occurs as the mud, bearing the drill cutting rises through the drilling formation.
By passing the liquid, or at least that portion of it which includes all particulate matter, through a magnetic separator, substantially all, or at least the greater part of, the unreacted oxide particles are recovered for re-use. Since the unreacted particles are characterized by low remanent magnetism, after the magnetic separation they are readily re-suspended in such liquid.

Description

7~

~ SE OF M~NETIC SEP~R~TION IN SCAVENG~G Ery~oGEN ~SULFIDE
~hn; C.~1 Field:
This invention relates to scavenging ~lyclrogen sulfide, as enc,ountered in well ~rill;ng or in waste or geothermal water or hy~Lv~dLLv~l oil~ by use oE an ex~ess c~Jantity of m-agnetic iron oxide particles; the excess is m-agnetically separa-ted for re-use.

Background Art~
~ dL~y~l sulfide is often present in drilling ~orma-tions and is a by-~Lu~L of sane ~hPm;c~l processes. ~ L~V~L en~vw,LeL~d, it is a la contaminate that must be Pl;m;n~P~
~ y~L~3~1 sulEide en~ L~L~d in drilling oil or cJaS wells may be dangerous or even deadly. It may be s~dv~y~d by additives -to the ~rill;n~ mud. Cne such additive and the process of using it is dis-closed in U. S. Patent ~o. 4,008,77S. i~Irther, in my U. S. Patent No.
4,344,842, it is ~;~cl~d ~hat such an additive may be added directly to hydroc~rhnn oil c~nt~min~t~ by h~drogen sulfide, the scaven~ing taking place in the oil without any other medium.
The additive so ~1~11;7~ is a umc~ue iron oxide particle character-ized by an Fe304 crystalline phase but ;n~ in~ an Wl~L~ ~ Fe203 moiety; on reac,~ion with hydrogen sulficle an enviLu~ ,Lally safe reaction ~LV~t iS formed which is substantiall~ acid stahle. The reaction p,roduct is non-masnetic, whereas the u~reacted particles are a-ttracted to a magnet. When used as a drilling mud additive, the extent to which the particles have been exhausted has been monitorecl by magnetic differen-tiation.

~ 1Osure of the Invention:
The present invention is a process util;7;ng the described iron oxide particles to scavenge hydrogen sulfide by suspension in contaminated liquids such as water, hydro~rhnn liqlids or drilling mud. Utilization of this process provides effective, safe and speedy hy~l~y~l sulfide scavenging without accumulation of partic~late matter in the liquid and 10 without wasting the reactive particles.
The reactive iron oxide particles employed are onnq;~red to be ferri-magnetic, in the sense that, while they are attracted to a magnet, they retain little r~m~n~nt magnetism. Thus, once magnetically separated, they do not attract one another and may be readily re-sn~pPn~P~. Uniquely, these ferri-magnetic iron oxide particles react ~th llydl~y~il sul:Eide to form a s~sk~lLially non-magnetic envlL~)rl"~"l~11y safe particulate product of reaction. ~hus, an excess quantity over that required for scavenging is used in the suspension and the unreacted particles are re-used in a sll~pPn~;~n after being magnetically separated.
These characteristics make the described iron oxide particles ~qpPc;~11y useful in ~1im;n~tin~ l1YdLOY~11 sulfide from ~r;11;ng muds.
Typically, the iron oxide particles æe s1l~r~n~Pd in a water based drilling l~ud in a quantity subs~n~1~lly in excess over that required to react the H2S expected to be en~v~l~L~dO The mud with its s1-~rPn~d particles is circulated through the ~r;ll~ formation, reacting with hydlu~l sulfide encountered, and returns laden with non-magnetic pc~rticu-late product of reactio~ as well as the abrasive solids such as sc~nd and ~rill;n~ cuttings. Thereafter, substantially all of the particulate matter is con~e~ d~ed onto a first portion of the drilling mud; while the rPm~;n;n~, subst~nti~lly particulate-free portion of the m~d (herein referred to c~s the "second portion"] is retained for re-use. me first ~ c~lLl~Led portion of the ~r;ll;ng m~d is then passed through a magnetic separator. Subst~n~;~lly all, or at least a greater portion, of the excess unreacted iron oxide particles are separated out fro~ the mud and are collected for re-use. The part;~ll~tP product of reaction and other abrasive solids are next separated fro~ the first portion of ~he mud by '7~'~

3~

a ~ullv~linn~l solids separator. The now substr~ntially particulate-free first portion of the drilling mud is recombined with the second portion, above referred to, in r~;n~q~ for re-cir~-l~t;~n. T~le magnetically separated iron oxide particles are re-suspended in the mud toyether 5 with a quan~ity of new reactive ferri-magnetic iron oxide particles, in order to restore -the drilling mud's hydroyen sulfide scavenginy ability.
To scavenge onnt~min~ting H2S from oil, an excess quantity of the described iron oxide particles is mixed into suspension, for reaction.
Next, the hydrocarbo~ liquid containin~ the excess iron oxide particles, 10 which remain unreacted, the partic~late product of reaction and any other solids, is passed Lllr~Llyh a magnetic separator. These unreacted iron oxide particles so separated by the magnetic separator are collected for re-use. Electrostatic precipitation ~l;m;n~tes the r~m~;n;ng particu-late matter from the hydrocarbon liquid. The oil is now s~dvr~llyr~d, 15 par~ te-free and ready for ut;l;~t;~n.
'rO scavenge waste water or geothermal water, an excess quantity of the described iron oxide particles is sl1~prPn~rPd in it. A conr~llLlc~Lion step follows; for example, the water may be diverted to a settling pond equipped with a weir; so ~hat on settling, subs-tantially all particulate matter is cnn~"l ~lP~l into a first portion of the water. This portion is passed through a magnetic s~drdLr~L, and, by it, the excess unreacted iron oxide particles are sep æated from t~e water, ~or re-use of these particles. If the water is to be used, the particulate product of reaction and any other solids are then separated out by llfil;~ing a 25 c~llv~r~ n~l solids separator. Likewise, the second substantially particu-late~ree portion of the water may ke used or ~ h~rged.

Best Mbde for Carrying Out the In~entio~:
The particle lltili~ in practicing this in~ention are ~1~Eelcbly the synthetic Fe304 particles disclosed in U. S. Patent No. 4,008,775.
'rheir average size is approximately six to eight microns. 'rhough identi-fied by X-ray ~iffra~tion as erystalline Fe304, ESCA/AUGE~ s~ectrosc~py analysis indieates a surface coating of am~rphous Fe203; this ~nm~n~ition along with the extraor~in~rily large effeetive surface area of the synthetic particles may aecount for their exceptional reactivity~ Such partieles are re~erred to in this disclosure as Fe304.
The ~p~rihed synthetic Fe304 particles are onn~ red to be ferri-magnetic, in the sense that while they are responsive ~o a r~gneticforce they do not become pern~nently magnetized by it. Thus, after being magnetically separated and collected, the parti.cles separate readily from each othex^ and are readily re-suspended in a liquid.
As disclosed in said Patent No. 4,008,775 these iron oxide particles react with H2S to form a par~ lAte product of reaction which is envi-lullls~lLally safe. mis particulate pLuLluL_L of reaction is also substan-tially non-mdgnetic.
In the process of the present invention, speedy and sa~e scavengin~
10 is effected by employing in suspension an excess quantity of the particles, and then effectively di:fL~I~ltiating between the unreacted excess parti-cles, which remain magnetic, and -the reacted non magnetic particles. As shown in the issued patent LL-LeLLL~d to, the particulate product of r~ n is principally FeS2 and may ;n~ other non-magnetic substan-15 tially stable iron-sulphur ~....~-~lds, all of which reaction products are generally L-~f~ d to in this disclosure as FeS2. me reaction with H2S
may initiate within the amorphous Fe203 and proceed into the crystalline core portion; the prin.~ l reaction o~ 7rr;ng in the core appears to be essentially 3 4 6H2S ---73 FeS2 + 4~2 ~ 2~2-Tests of magnetic recovery of the ~-~f;n~ iron oxide pc~rticles were made by an ;nLlP~Pn~ nt test la~-ciLoLy, which reportecl as follows:
The equiF~ t used was an Eriez (-trademark) Lc~bOLdLUL~ l~et Drum, ~del L-8~ cadjusted to give equivalent recoveries of a 1,000 gauss high 25 gradient wet drum and an Eriez (LLdd~l~Lk~ Labo-dLoL~ ~.Tet High Tn~nC;ty Magnetic Separator (WHIMS), Mcdel Lr4~ equipped with medium e~anded metal oollection matrix.
Ihe -test procedures were as follows:
About 2kg of sample iron oxide particles were ~ rri~ in water and 30 passed through the l~l~n,~lo,y wet drun. The slurry was about 10~ solids.
The non-~agrletics were filtered and then washecl LI~U~I1 the Lr4 with the ba~hy~ d field set to 8,000 gauss. All final p.roducts were filtered, dried and ~e;~hP~
r~he tests were evaluatecl as follows:
At standard ~u~lc~lLLaLions, this sample sh~wed a 9S 3~ recovery on the wet drum. mis ;n~ t~ that the recovery curves for n~re dilute slurries will follow a SL~1dd1d recovery curve for wet drums. I'he standard recovery curve shows an 85% to 88% recovery in the concentra tion range of 9 grams per gallon (1 pound per 50 gallons). rrhis curve also shows that the recovery w~uld be less than 5% when the ~ LLd-tion drops to 0.54 grams per gallon (1 po~nd per 840 gallons).
Use in ~r; 11; n~ muds:
One of the dangers of drilling wells is that l~xpectedly large concr~lL~dLions of hydrogen sulfide may be en~lLeL~d. These concen-tra-tions are sometimes deadly. rme pos~ih;l;ty such a concentration mdy be encountered warrants the llse, in the ~r;lling ~d, of a quantity of the 10 s~d~ly~r much greater than may actually be reacted. The described iron oxide particles have ~x~ nt rhRol~ l properties so that they may serve, in whole or in part, as the weighting agent.
~ or use in drilling mud the described iron oxide particles are s~pPn~7~ in ~he drilling mud in amounts r~n~inr3 normally up to twenty 15 pounds per ~harrel. The ~r711;n~ mud, containing the excess guantity of iron oxide particles, is circulated U~uuyll a drill bit and carries th~-~fr~ll abrasive solids such as sand and drill cuttings, the particu-late ~ u~L of reaction with hydrogen sulfide, generally l~Ll~d to as FeS2 and the excess ~u~si~"li lly unreacted iron oxide particles, Fe304.
20 The quantity o~ FeS2 formed is greater in weight than the quantity of reagent Fe304 particles; and since the abrasive solids were not there-tofore present in the mud, the weight composition and rhP~ ;c~l prop-erties of the ~7r;11;n~ mud may be altered on circulation and use.
Drilling mud ~ erLies are r~n~ red critical to the ~rilling 25 process. By the following extractions and additions, the circulated used ~r;llin~ mud may be substantially freed of sand, drill cuttinygs~
and particulate pl~u~L of reaction and restored to its orlginal ccm-position and rheolcgy, again containing the chosen quantity of reactive iron o~ide par~iclesO
Qn rising to the surface, the used drilling mud is first passed Ll~lv~yh a screen of conveni~nt size, roughly between 35 mesh and 100 mesh, to ~l;m;n~te the larger drill cuttinys, etc. The mud is then preferably passed Ll~uyl~ a cyclcn~ type sep æator; ~y subjecting the drilling mud to a c~n~rifugal force, substantiall~ all of the particu-35 late matter is con~lLLdted into a first portionl for example la% or less, of the drilling mud. Ihe second particulate-free ~ortion of the ~r;ll;ng ~d, ;n~ln~;ng any colloids used, is retained for re-use. This extraction and con ~ l~ld~on reduces the volun~ of liql1d and particulate kZ~3~7 matter to be passed through the next ~gnetie separation step, which may make f~;h]~ the use of a smaller capaclty magnetic s~al~lLv~ or increase its effectiveness.
On p~sing the cnnc~n~rated first portion of the used drilling mud, 5 contaim ng the partieulate matter, t~rough the magnetie s~dLrlLu~/ at least a greater portio~ of the suhstantially unreaeted iron oxide parti-cles will be separated out of the ~7r;11;ng mud. These partieles so extracted are collected for re-use. rrhe extent of the extraetion is dependent upon sueh faetors as the Pff;~i~nry with whieh the drilling 10 mud is L~uyhL into eontact with the magnetic sep æ ator; practical ennr;iA~r~-tions are the eapaeity of the separator and the flow rate and viscosity of the liquid.
After the magnetie separation, there are furthQr separated from this first portion of the drilling mud the abrasive solids and the 15 particlllate product of reaction formed; any c~lv~llLional solids separa-tion process may be used, sueh as s~;m~ntation or eQntrifusing. ~is last extraction renders the first portion of the drilling mud substan-tially free of partle~ t~ matter. The retained seeond portion of -the drilling mud, ~nnt~;ning sueh eoll~ir7~ as were used, is re-~nmhin~fl with 20 the first portion of the ~7rill;~ mud. m e salvaged iron oxide particles are then returned to the re-c~mh;n~ 7r;11;n~ mud, and a quantity of new iron oxide particLes i~ also added~ restoring the ehosen quantity of magnetie iron oxide particles to -the ~r;ll;ng r~wd, and thus restoring i-~s ahilit~ to S~dv~lly~ hydro~en sulfide. The fluid is now ready for 25 re-use; and this process is r~peated upon continuing re cir~ll~t;~n.
The reacted partieles, as well as any of the fluid not re used, are envi~ .taLly safe and may be diseharged or disposed of by conveying to a simple waste heap.
V~ hle ~ ls of ~r;ll;n~ muds are sometimes salvaged after 30 ~7r;17;ng is eompleted, for re-use ~ wh~re. Tb do so is especiall~
worthwhile where as here, an exeess of reaetive partieles is used. On eompletion of ~r;ll;ng~ the excess unreaeted iron oxide particles may be magnetically s~p~r~ as above descrihed and salvaged for re-use else-where. ~ccordingly, although the reactive particles are employed in an 35 excess amount during drilling, to provide a margin of safety in the event of unexpected large ~m;~ n.~ of hydrogen s~ide, the prooess is ec~n~m;~1 because the unreacted particles are separated from all sand and drill cuttings and salvaged for re-use.

Vse in hydrocarbon lic~uids:
If the cont~m;n~t~d liquid is a hydrocarbon liquid, this process will provide effective scavenging, whether the hydrocarbon licruid is crude or refined oil.
A quantity or ferri-magnetic iron oxide particles ,lre ~us~lded in the c~nta~;n~ted hydrocarbon liquid. rrhis q~ntity is in excess over that required to react the hydrogen sulfide, thus speeding the reaction time.
Scavenging of hydrogen sulfide cnn~;31nP~ in anhydrous non-ac~eous lic~uids is described in my co-pPn~in~ arrli~ation, abcve referred to, and the considerations given to mixing and agitation are appl;c~h1 here.
After reaction of the hyclrogen sulfide has occurred, the hydrocarbon liquid~ cnnt~;n;ng the exoe ss unreacted ferri-magnetic iron oxide particles, the non-magnetic particulate product of reaction and any other solids, is passed Ll~uyh a magnetic S~r~a~. Su~statl~ially all, c)r at least a greater portion of the unreacted iron oxide particles is separated out of the hydrocar~on liquid and collectea for re-use.
r~he non-p~r~ t~ product of reaction and any other solids are next separated out of the hydrocarbon liquid by use of any conventional solids separation process, such as se~;mPntation or centrifuging, or, for even greater effectiveness, ele~Ll~sLaLic precipitation. These enviL)""~"I~l1y safe solids may be ~;r~rnse~ of simply, as on r~n open waste heap. After this last e~traction, the hydrocarbon liquid is -thor~
ou~hly scavenged, envil~l",~tlLally safe, substantially particulate-free and is ready for 1lt;~ tion.
Use in water:
If the conta~unated liquid is water, such as industrial waste water or ~nn~nced geo~h~rm~l steam, the described ferri-magnetic particles are sl3~Pn~ in the water containing the hydrogen sulfide. I~e quantity of iron oxide particles so added to the contaminated water is in excess of that required to react the hydrogen sulfide present, ~hus to assure glLick and effective scavenging. The hydrogen sulfide particles are contacted and reacted by the described ferri-m~gnetic iron oxide parti-cles, formin~ the non magnetic particulate product of reaction. Inorder to speed the reaction time the water may be agitated.
After effective scavenging has occurred, all the particulate may be con~ L~ed in a first portion of the water small enough to be processed ~jlq ~ ,rr~
J ~ r ~ O

b~ an ec~n~m;~11y sized magnet.ic separator. For such concentration any process may be used; for e~a~lple, the water may be allowed to sett.le in a settling pond equipped with a weir. 'rhe rPma;n;ng or second po.rtion of the water, substantially particulate-free, will flow over ~he weir. Gn 5 pA-~s;ng the first con~ LLdLed portion of the water through the magnetic sep æator, all or at least a greater portion of the unreacted ferri-magnetic iron oxide particles will be separated. ~rhe iron oxide particles so separated are collected for re-useO
If the water is to be then use , the non-particulate product of rPArt;~n and any other solids are then sep æ ated frcm this first portion of the water by any ~vl,vr~r~ nA1 solids separation process, as by diversion into a settling pond. Both po.rtions of the water are then usable. Alter-natively, the water, itself envi~ k~ lly saFe and containing the envi~ "~ 11y safe reaction product and other solids, rnay merely be discharged.
Even though some o~ the magnetically separated iron oxide particles may contain some reacted FeS2 m~lP~11P.~ the correlation between reactivity of the particles and their magnetic characteri~stic is so great a~s to warrant the reference, in this disclosure and clairns, to magnetically separable particles as being subst~nt;~11y unreacted V æ iations from the processes above described will be app æent to those s]cilled in the art. For example, if the present ferri-rnagnetic particles are u~sed in a drilling fluid in cnmhin~ti~n with a conventional non-magnetic weighting agent ~such as barite, the descr~bed process will nevertheless be useful For salvaging and re-using the unreacted ferri-magnetic particles, as well as the c~11O;~ The barite, being non-magnetic, will be separated out along with o-ther non-magnetic particles, that is, the reacted particles, sand and drill cuttings. If i.t :is de~Prm;nP~ that these non-magnetic particles taken together are not too ahrasive to serve as a wP;~ht;n~ agent along with a replP.n;~hPd quantity of unreacted particles and colloids, they may he so re-used; otherwise, such all separated non-magnetic solids should be discarded Industrial ~pp1;~h;1;ty:
A prinr;~l use of the present invention is ~n s~dv~n~in~ L~
sulfide from ~r;11;n~ m~ds ~y the use of a quantity of the particulate iron oxide .~;gn;Fi~ntly in excess of that required to actually react Z ~3'7 the hy~rogen sulfide, so as to provide a margin of sa~ety. ~l~agnetic recovery of the excess L~ld~L~ the p~.ocess ec~n~ nc~ther justi~i-cation for use of an exc~ess is tha~ the particles serve at least in part as a ~ hting agent.

.....

Claims (2)

Claims The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In scavenging hydrogen sulfide from a hydrogen sulfide contaminated liquid, the process of suspending in a hydrogen sulfide contaminated liquid a quantity of ferri-magnetic iron oxide particles of the type which react with hydrogen sulfide to form a substantially non-magnetic environmentally safe particulate product of reaction, said quantity being in excess over that required for the reaction of such hydrogen sulfide, contacting and reacting the hydrogen sulfide with the said iron oxide particles and thereby forming such non-magnetic environmentally safe particulate product of reaction, the excess iron oxide particles remaining substantially unreacted and retaining their ferri-magnetic characteristic, then passing the liquid containing the particulate matter comprising the excess unreacted ferri-magnetic iron oxide par-ticles, particulate product of reaction and any other solids, through a magnetic separator, and, by it, separating and recovering therefrom substantially all or at least the greater portion of the said unreacted iron oxide particles, separating out from the liquid such non-magnetic particulate product of reaction, along with any solids present, whereby to dispose of same without hazard to the environment, recovering the purified liquid and returning the unreacted iron oxide particulates to the contaminated liquid treatment step.

2. In well drilling using a drilling fluid, the process suspending in such drilling fluid a quantity of ferr-magnetic iron oxide particles of the type which react with hydrogen sulfide to form a substantially non-magnetic, environmentally safe particulate product of reaction, said quantity being in excess over that required for anticipated reaction with such hydrogen sulfide as may be encountered in drilling, circulating such drilling mud downward through a drill bit while drilling and then upward through such formation, thus incorporating drill cuttings into the drilling fluid and thus contacting and reacting, with the said iron oxide particles, any such hydrogen sulfide so encountered, whereby to form such non-magnetic environmentally safe particulate product of reaction, and leaving at least a substantial portion of said iron oxide particles substantially unreacted and retaining their ferri-magnetic characteristic, then passing the drilling fluid, containing the particulate matter comprising the drill cuttings, unreacted ferri-magnetic iron oxide particles, and such particulate product of reaction, if any, through a magnetic separator, and, by it, separating and recovering therefrom substantially all or at least the greater portion of the said unreacted iron oxide particles, then separating out from the drilling fluid substantially all the remaining particulate matter including drill cuttings and any such non-magnetic particulate product of reaction, whereby to dispose of same without hazard to the environment, recovering a particulate-free drilling fluid portion, sand separated unreacted ferri-magnetic particles as may be substantially equal to such quantity, if any, of the non-magnetic particulate product of reaction.