k!oa)f- 4 - / r o S &

Transcription

1 5 * a k!oa)f 4 / r o S & * Sanda s a multprograrn faboratory operated by Sanda Corporaton a Lockheed Mann Company for the Unted States Department of Energy under contract DEACWWf85w # J U 9 6)(87 OSV Socety of Petroleum Engneers Mcrosesmc and Deformaton magng of Hydraulc F the C Sand nterval GR/DOE MSte Project NR Warpnsk SPE Sanda Natl Labs and PT Branagan SPE and RE Peterson SPE Branagan & Assoc and JE Fx SPE'Jarnes E Fx & Assoc and JE Uhl and BP Engler Sanda Natl Labs and R Wlmer Branagan & Assoc Copyrght 997 Socety of Petroleum Engneers nc Ths paper was pfepared for presentaton at the 997 SPE Annual Techncal Conference and Exhbton held n San Antono Texas 58 October 997 Ths paper was selected for presentaton by an SPE Program Cmmnee followng revew of nformaton mntaned n an abstract submtted by the author@) Contents of the paper as presented have not been revewed by the Socety of Petroleum Engneers and are subject to correcton by the author@) The materal as presented does not necessarly reflect any poston of the Socety of Petroleum Engneers ts offcers cf members Papers presented at SPE meetngs are subject to publcaton revew by Edtoral Commnees of the Socety of Petroleum Engneers Eledronc reproducton dstrbuton or storage of any part of ths paper for commercal purposes wthout the wrtten consent of the Sodety of Petrdeum Engneers s prohbted Permsson to reproduce n prnt s restrcted to an abs3act of not more than 3 words; llustratons may not be coped The abstrad must mntan conspcuous acknowledgment of where and by whom the paper was presented Wrte Lbraran SPE PO Box RchardsonTX U S A fax Abstract Sx hydraulcfracture njectons nto a fluval sandstone at a depth of 43 ft were montored wth multlevel traxal sesmc recevers n two wells and an nclnometer array n one well resultng n maps of the growth and fmal geometry of each fracture njecton These dagnostc mages show the progresson of heght and length growth wth flud volume rate and vscosty Complextes assocated wth shut downs and hgh treatment pressures can be observed Valdaton of the sesmc geometry was made wth the nclnometers and dagnostc procedures n an ntersectng well Fracture nformaton related to deformaton such as fracture closure pressure resdual wdths and fnal prop dstrbuton were obtaned from the nclnometer data ntroducton Contrary to expectatons based on smple models hydraulc fracturng s provng to be a complex process that s stll not adequately represented by theory The reason for ths s clear as models assume that the earth s a homogeneous sotropc contnuum when n fact the reservors whch are fractured are hghly dscontnuous and varably ansotropc and heterogeneous Snce current models are ncapable of dealng wth ths complexty n anythng but an ad hoc manner' further understandng of hydraulc fracturng s not lkely to progress very rapdly wthout an ablty to measure mage or observe fracturng processes under n stu reservor condtons A glmpse at the complexty of fracturng n real reservors s now avalable from several cores through hydraulc from lmted mneback and from varous dagnost~s~*'~'~ From these relatvely few measurements complex features such as multple fracture strands secondary fractures Tshaped fractures redrecton of fracture orentaton due to producton neffcent growth across beddng complex proppant transport and other unexpected features have been seen From ths lmted samplng one would conclude that the fracturng process s poorly represented by most models However t should also be stressed that the results found at the end of a treatment ( e g as n a cored or mnedback fracture) may not be a good representaton of the actual process durng fracturng snce all complextes wll be seen whether or not they had any sgnfcant effect on the mechancs of the process Separatng out rrelevant features s dffcult usng only postfracture snapshots of the process For the reasons noted above t s clear that the optmum dagnostc would provde a realtme contnuous mage of the fracture growth process Currently there s no envsoned technology for drectly vewng the fracture but some fracture parameters can be ndrectly montored usng downhole sesmc recevers and downhole nclnometers The applcaton of these two technologes n the Csand nterval at the MSte faclty s the subject of ths paper MSte The MSte feld experments" located at the prevous Multwell Experment ste n the Pceance basn of Colorado are cofunded by the Gas Research nsttute (GR) and the US Department of Energy Detals of the MSte layout and nstrumentaton are gven n prevous paper^^*'^^'^*^'^^ and are only brefly repeated here The reservors undergong testng are fluval Mesaverde sandshale sequences so the technologes developed n ths dffcult envronment are translatable to many other reservors Results of prevous tests are found n several papers and reports A plan vew of the ste s shown n Fgure and a schematc of the well nstrument and sandstone layout are gven n Fgure 2 The ste conssts of one treatment well (MWX2) one montor well wth cemented traxal sesmc

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3 DSCLAMER Ths report was prepared as an account of work sponsored by an agency of the Unted States Government Nether the Unted States Government nor any agency thereof nor any of ther employees makes any warranty exprtss or mpled or assumes any legal lablty or responsblty for the accuracy completeness or usefulness of any nformaton apparatus product or process dsclosed or represents that ts use would not nfrnge prvately owned rghts Reference heren to any specfc commercal product process or sentce by trade name trademark manufacturer or otherwse dots not necessarly consttute or mply ts endorsement mm mendaton or favorng by the Unted States Government or any agency thereof The vews and opnons of authors exp~~ssed heren do not necessarly state or reflect those of the Unted States Government or any agency thereof

4 NR WARPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER recevers and baxal nclnometers and one cased observaton well for wrelne run tools (MWX3) Also shown n the fgure s an ntersecton well (WC) wth a devated lateral that penetrates through the created hydraulc fracture(s) The openhole secton of the lateral s shown as the dashed secton The montor well provdes the nstrumentaton for valdatng the sesmc results Thrty traxal recever statons wth lownose (4pg) wdebandwdth (222 Hz) accelerometers provde hgh qualty mcrosesmc data from whch the source can be accurately located n the same well sx baxal tltmeters wth nanoradan resoluton provde nformaton on the mechancal deformaton of the formaton whch s used to valdate the sesmc results as well as provde valuable nformaton related to rock deformaton The 7n cased observaton well s used for multlevel wrelnerun traxal recever arrays of the type that wll be used n a commercal fracture dagnostc servce Ths array uses the same accelerometers as are grouted n the montor well and the multevel feature also provdes for hghly accurate mcrosesmc event locaton The montor well results wth many more levels to apply n locaton algorthms are used to verfy the data obtaned from the wrelne recever arrays Addtonal nformaton obtaned n the treatment well such as bottomhole pressure spectral gamma logs of radoactve tracer dstrbutons and sesmc surveys are used for detaled fracture modelng and addtonal dagnostc nformaton Detaled stress rock property and reservor property data are also avalable for these reservors and are used for fracture models fmte element deformaton models and analyses of the mechancal response of the formaton to the fracture treatment Addtonally crosswell sesmc surveys were conducted to determne the pwave and swave structure at the ste Sesmc data were obtaned wth 5ft source and recever spacngs n the treatment and montor well respectvely and the permanent 3f spacng of the cemented recevers n the montor well The sesmc source was an argun whch provded excellent pwaves and generally good s waves Both p and s tomograms have been produced Of crtcal mportance for valdatng the sesmc results was the lateral well2' whch ntersected the expected fracture plane at a pont 287 ft from the treatment well (MWX2) and at an elevaton approxmately /3 of the thckness of the sandstone from the bottom of the sandstone The lthology of the C sand conssts of an estuarne sandstone found near the top of the Mesaverde formaton Fgure 3 shows a gamma log of ths sandstone taken from the treatment well The stress contrasts around the C sand as determned prmarly from mcrofracture stress measurements are shown n Fgure 4 Stresses n the B and C sands were confrmed usng the nclnometers to the record the pressure at whch openng begns For modelng purposes more detaled calbrated stress logs were also developed Durng Csand testng sx dfferent fracture njectons usng two dfferent fluds were montored mportant nformaton on the njectons s gven n Table Table Treatment Data Data Analyss nstrumentaton conssted of traxal accelerometer arrays n both the montor well and MWX3 observaton well and a baxal nclnometer (tltmeter) array n the montor well Data analyss conssted of locaton analyss of the mcrosesmc events from whch maps of fracture growth were generated elastc modelng of the measured nclnatons from whch fracture heght estmates were derved and correlaton of these results wth other nformaton derved from fracturenjecton and ntersectonwell data Mcrosesms The analyss of the mcrosesmc data was performed n the usual manner for a large number of recever statons~459 Only events that were detected on several recevers were analyzed and used Pwave and swave arrvals were selected and the partcle moton of the ntal p wave was determned usng a regresson based on crcular statstcs The drecton to the source was found from the average partclemoton orentaton not ncludng any obvous outlers The dstance to and elevaton of the mcrosesmc source were found from a jont regresson of the dstance equatons for the two phases r 2 + ( Z z)' = 4) 2 v;(p and where T s the horzontal dstance from the montor well to the source z s the elevaton of the source t s the tme at whch the mcrosesm orgnated Vp and Vs are pwave and swave veloctes z s the elevaton of the " recever and tp and ts are the pwave and swave arrval tmes at the " recever Usng ths approach a best ft locaton of the mcrosesm and welldefned uncertantes can be readly calculated nclnometers nclnometer data were processed n the same manner as descrbed n Branagan et al" For shortterm treatment montorng nclnometers were zeroed at the begnnng of the fracture njecton and changes n the tlt feld normal to the fracture (the most senstve orentaton) were contnuously montored The resultng nclnaton feld was mmedately compared wth several analytc models ncludng

5 M~cRoSESMC AND DEFORMATON MAGNG OF HYDRAULC FRACTURE G R O W H AND GEOMETRY?D pennyshaped and flat ellptc crack (3D) geometres A fmal analyss of the results generally ncluded fnteelement calculatons to fully account for stress and modulus varatons* mportant controllng parameters for the nclnatons nclude the pressure n the fracture fracture length heght and azmuth the modul of the varous rock layers and the stress n the layers contactng the Fracture Unfortunately at the tme of these tests the nclnometers were begnnng to degrade (they had been n the well for two years) and the deformaton data on fracture heght was not as accurate as B sandstone results nclnaton data were also examned for long term resdual effects (proppant placement and fnal propped wdth) and for ntal openng of the fractures (to provde closure stress data) Fracture Experments Fracture experments n the C sand nterval (see Table ) were conducted between August and December 996 and usually were spaced wth several weeks between treatments to reequlbrate the reservor wth the excepton of C and 2C (two days) and 5C and 6C (two days) Fgure 5 shows a correlated plot of pressure data from all sx njectons for reference to the followng dagnostc results Closure stress s approxmately 35 ps the overburden stress s approxmately 46 ps and the maxmum horzontal stress s at most 42 ps n the C sand njecton C (Breakdown) The frst njecton n the C sand conssted of a 95 bbl breakdown usng a crosslnked 4# borate gel pumped at 2 bpm The purpose of the thck flud was to mnmze pressure drops near the wellbore Fgure 6 shows plan and sde vews of all of the mcrosesmc data for ths njecton The fracture appears to have grown upward about 23 ft partcuary on the west wng whle t has generally avoded the lower part of the C sand The fracture shape s also relatvely symmetrc wth a wng length of about 2 ft Addtonal nformaton about hydraulcfracture mechansms can often be gleaned from observng the tmedependent growh of the fracture Fgure 7 shows plan and sde vews of the mcrosesms recorded after 5 mnutes whch s the pont where shutn occurred At ths tme there are relatvely few mcrosesms and they only show fracture mowth out to 3 ft on each wng Thus an addtonal 7 f of len& growth occurred after shut n The sde vew ndcates that ntal growth was wthn the center of the C sand and above the C sand on the west wng Relatve to the ntersecton well njecton C resulted n a fracture whch extended at most 2 ft on the east wng Thus there was no evdence from the mcrosesms that the fracture contacted the ntersecton well (at a dstance of 287 ft from the treatment well MWX2) nor was there any ndcaton of any pressure dsturbance n the ntersecton well u 3 Fracture 2C (Approach Mnfracture) njecton 2C whch was conducted on August was desgned to be a lneargel mnfrac whch would approach the ntersecton well wthout httng t The desgn volume was 25 bbl at a desgn rate of 2 bpm However recognzng that fracture growth s very uncertan n these complex fluval geometres t was decded that at the frst sgn of pressure ncrease n the ntersecton wel the treatment would be termnated As can be seen n the pressure data of Fgure 5 the 2C njecton ncluded a stepup pump at the begnnng of the njecton and then a quck stepdown and shutn for nearwellbore pressuredrop estmates Fnally njecton started agan at about 9 mnutes and contnued untl a pressure ncrease was observed n WC The maxmum net pressure for ths njecton was about 9 ps The pressure ncrease n the ntersectng well was observed after pumpng 3 bbl and the treatment was termnated wth a total njected volume of 32 bbl Detals of the ntersecton pressure behavor are gven n Branagan et al but just the tmng of the pressure ncrease provdes a well defmed fracture length for comparson wth the mcrosesmc results Fgure 8 shows the mcrosesmc fracture geometry at the tme that pressure was observed n the ntersecton well (at a dstance of 287 ft) At the tme of ntersecton the mcrosesmc length s 29 ft + l o ft on the east wng thus valdatng the accuracy of the mcrosesmc length results n ths test the west wng length s also nearly 3 ft Fgure 9 shows the plan and sde vews of all of the mcrosesms recorded durng the 2C njecton The njecton results n an approxmately N74 W azmuth wth an east wng length of at least 4 ft and a west wng that s slghtly less All of the addtonal growth n Fgure 9 as compared to Fgure 8 occurs after shut n On both wngs the fracture appears to avod the lower part of the C sand There s no upward growth on the west wng of the fracture but the east wng shows upward heght growth startng about 5 f east of the wellbore As noted prevously these 2C mcrosesmc results are the most mportant aspect of ths entre C sand test sequence as ths experment proves that the mcrosesms provde an accurate mage of fracture length However some nterestng results wth respect to fracture growth can also be seen n these data The fracture growth upward on the east wng s somewhat unusual as heght growth s generally observed near the wellbore where the pressure s the hghest One possble explanaton s the exstence of addtonal sandstone unts at the top of the C sand on the east wng Such an nterpretaton s supported by the crosswell sesmc survey whch ndcated that the C sand shfted upward n the secton between MWX2 and the montor well Snce ths upper sand unt does not extend north nto the treatmentwell regon t s lkely that t extends eastwest Ths hypothess was confrmed by sedmentary analyss Based on ths nterpretaton the fracture s merely followng the sandstone channel and there s

6 4 NR WARPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER no outofzone growth The fnal fracture length of 4 ft and the mnmal heght growth compared to njecton C shows that there are sgnfcant effects due to the vscosty At a volume of 95 bbl of crosslnked gel the breakdown njecton acheved a fnal length of 2 ft Wth only 4% more volume than C the lneargel 2C njecton acheved double the length even whle experencng greater leakoff due to the lower vscosty and the long shutn perod However ths dfference n length extenson was acheved even though net pressures dffered by only 5 ps njecton 3C (Full ntersecton Mnfracture) njecton 3C whch was conducted on August was a repeat of njecton 2C except that a full 247 bbl were njected The pressure response n and postfracture loggng of the ntersecton well (see Branagan et a*') ndcated that the nterconnecton after the 2C treatment was mnmal t was hoped that ths poor connecton could be remeded wth a larger lneargel treatment that would more adequately ntersect the WC well The complcated pressure response durng njecton 3C as shown n Fgure 5 s due to stepup stepdown and shutn perods Most of the volume was njected n the latter part of the test at a rate of 22 bpm and a net pressure of about 95 ps Mcrosesmc results of njecton 3C are shown n plan and sde vew n Fgure Ths h c t u r e has an njected volume of only 25 bbl and a farly hgh leakoff because t s a lnear gel yet the fracture lengths are almost 5 ft on the east wng and more than 4 ft on the west wng The azmuth through all three ntal njectons have been N74"W or N75"W Ths fracture shows some slght evdence of heght growth near the wellbore The upward growth on the far east wng whch was frst seen n the 2C njecton s also obvous n ths test The ntersecton wth WC (pressure ncrease n the ntersecton well) occurred relatvely early n the treatment but as n njecton 2C t was not a very conductve connecton The mcrosesms suggest that the hydraulc fracture may have been mostly above the ntersecton well snce lttle mcrosesmc actvty occurred n the lower C sand on the east wng Ths test also showed the rsng fracture behavor on the east wng but t s obscured somewhat by the ncreased heght growth near the wellbore The nclnometers provded mportant longterm nformaton about resdual deformaton after unpropped fracture treatments Fgure shows the nclnatons recorded on the shallowest nclnometer durng and after the C3C njectons These data have been normalzed to the largest value (3C maxmum value) and show that the deformaton never returns to zero but nstead mantans a nearly 2% resdual expanson Ths expanson s nterpreted as beng prmarly a result of resdual openng as poroelastc effects would have dsappeared after reservor pressure equlbraton was complete (typcally a few days) t can also be seen that the magntudes of the tdal nclnatons are much smaller than the nclnaton magntudes nduced by the fracture treatments and thus do not cause any nterpretaton problems n ths downhole envronment njecton 4C (Hgh Energy ntersecton) njecton 4C conducted on November was a dual objectve test Approxmately bbl of 4LB/mgal crosslnked gel were njected nto the C sand at about 4 bpm n order to provde the opportunty for obtanng treatment well dagnostcs and to gve a fnal attempt at obtanng a clear ntersecton of WC To test the treatment well dagnostcs a fourlevel sesmc array was placed n the treatment well straddled over the C sand Unfortunately durng ntal njecton of water n the casng the turbulence of the thn flud nduced suffcent vbraton to loosen a lockng nut on the fberoptc cable head causng a break n the copper and fberoptc lnes (but the cable armor remaned connected and there was not a complete dsconnect of the tool strng) Thus no treatment well dagnostcs were obtaned durng ths test and the remanng dagnostcs were based on data from the montorwell recevers The njecton conssted of the prenjecton of 32 bbl of KC water whch was n the casng orgnally followed by the njecton of the crosslnked gel n two stages separated by a 5 mnute shutn perod for leakoff and nearwellbore analyses As seen n Fgure 5 the njecton of the gel occurs for about 5 mnutes followed by a 5 mnute shut down The mcrosesms recorded after the frst gel njecton and shutn perod are shown n Fgure 2 These data ndcate that consderable heght growth occurred on the west wng durng ths perod as well as length extenson on the order of 3 ft The addtonal heght growth s not surprsng snce the net pressure was greater than ps durng the njecton perod There s also an nterestng secondary feature runnng to the northnortheast Although t was speculated that ths feature could be a secondary fracture or actvated fault t was not consdered mportant untl after the 6C njecton showed the same feature and addtonal complexty as a result of t Gel njecton resumed at about 3 mnutes but at frst the gel would not move and surface pressures reached ther maxmum allowable at rates of only 2 bpm Fnally the flud started to move and rates were eventually bult to ther desgn values However at the pont where the gel began movng and fracturng clearly restarted there was a large burst of mcrosesmc actvty and a clear pressure connecton was observed n the ntersectng well Net pressures vared consderably durng the treatment but an average net pressure after fracturng resumed followng the shutn perod s roughly 2 ps All of the mcrosesms from the 4C njecton are shown n plan vew and sde n Fgure 3 Fracture 4C s clearly an asymmetrc fracture wth consderable heght growth The east wng length s 67 ft whle the west wng s only about

7 MCROSESMC AND DEFORMATON MAGNG OF HYDRAULC FRACTURE GROWTH AND GEOMETRY 4 ft Ths asymmetry occurred after the shutn perod and suggests that fracture extenson was affected by the shutn process essentally redrectng growth n the easterly drecton wth lttle extenson along the west wng Fracture growth upward s 6SO ft dependng on the locaton whle growth downward s about 5 ft but prmarly on the west wng Snce njecton 4C exhbted sgnfcant heght growth t s a good test case for evaluaton by the nclnometer array Fgure 4 shows the maxmum 4C nclnaton data at each of the sx statons durng the njecton as compared to 2D fnte element modelng based on a 2 ps treatment pressure The mesh and layerng used are the same as were employed for the B sandstone tests?' Only a 2D case was used because the fracture length on the east wng s 7 ft and prevous analyses had shown that after 6 ft of length there was no sgnfcant dfference between the 2D and 3D models Although the data cannot be exactly matched t s clear that the fracture heght on ths wng s on the order of 34 ft very comparable to the mcrosesmc results For ths calculaton all of the heght growth was upward The C sand results agan show that the mcrosesmc heghts are nearly the same as the mechancal heghts an mportant valdaton pont njecton 5C (TreatmentWell Dagnostc Test) njecton 5C was ntended to be a treatmentwell dagnostc test where a 4level accelerometerbased recever system was run n the treatment well to montor an njecton from the rat hoe below the perforatons As such only 48 bbl of 4LB/mgal crosslnked gel were njected at a rate of 3 bpm Treatment pressure for ths test are shown n Fgure 5 but there are no unusual features other than the relatvely hgh net pressure (4 ps net pressure) Data were obtaned from the treatmentwell array but are stll undergong analyss and are not gven here However the montorwell nstrumentaton recorded data from ths fracture and shows very smple fracture behavor compared to the prevous test Fgure 5 gves the plan vew and sde vew plots of the mcrosesms measured from the montor well alone These data ndcate that the fracture grew very symmetrcally wth lengths of nearly 5 ft on both wngs and approxmately 3 ft of both upward and downward heght growth Ths fracture s of nterest because of ts lack of complexty n contrast to the prevous test and also because of the comparable length to the 3C njecton even though the 3C njecton employed only half of the flud used n the 5C test The prmary dfference between the two tests was the flud vscosty although njecton 5C was pumped at a somewhat hgher rate njecton 6C (Stmulaton) njecton 6C was a propped treatment of a sze typcally performed per nterval n ths basn 25 LB sand and 2 8 bbl of 4LB/mgal borate crosslnked flud were njected at 3 bpm The pressure data for ths njecton are also shown n Fgure 5 The shape of the 5 pressure record appears normal but the fnal net pressure level of 9 ps s well above both the maxmum horzontal n stu stress and the overburden stress The mcrosesmc actvty after 5 mnutes of njecton s shown n Fgure 6 By ths tme the fracture had extended at least 3 ft on each wng but more mportantly a clear secondary fracture(s) had propagated to the northeast and another secondary fracture may have extended more northerly There s a large degree of certanty that these are secondary fractures because they are so much farther removed from the known fracture plane than any other mcrosesms detected prevously (except for the ntal detecton of ths same feature n the 4C njecton) They also be'om to occur after the net pressure exceeds the maxmum horzontal stress At ths tme the fracture s also relatvely well contaned wthn the C sand The fnal mcrosesmc mage s shown n Fgure 7 By the end of the treatment the magng showed several levels of complexty that are most easly seen n a tmehstory vsualzaton but wll be brefly descrbed here The secondary fracture propagatng to the northeast apparently spawned one or more fractures that propagated n the same orentaton as the prmary fracture These addtonal features occurred mostly durng the frst half of the treatment Later n the 6C treatment however mcrosesmc actvty fanned over a wde area to the south of the east fracture wng As seen n the edgeon vew of Fgure 8 all of ths actvty (left sde of plot) occurs n a narrow regon at the top of the C sand Ths type of actvty s most lkely a horzontal fracture but could also be several vertcal fractures propagatng n a narrow zone at the top of the sandstone t begns to occur after the njecton pressure exceeds the overburden stress Fgure 9 shows the nclnaton dstrbuton at several tmes from shutn through closure These dstrbutons have been normalzed by the maxmum nclnaton at each tme and can only be compared relatve to each other f the prop remans suspended n the flud through closure then the normalzed dstrbuton of the nclnatons should not change wth tme as only the absolute magntude of the nclnatons should change as the fracture slowly closes on an amount of proppant proportonal to ts wdth f however all of the proppant falls out to the bottom of the fracture then the shape of curves at later tmes wll dffer sgnfcantly from the orgnal shape at shut n As can be seen here there s only a small dfference n the shapes of the varous curves and t can be nferred that only small amounts of proppant have fallen out or convected to the bottom of the fracture Fgure 2 shows a longerterm vew of the nclnatons measured by the top nclnometer for both njectons 4C and 6C The resdual nclnatons for njecton 4C an unpropped treatment are about 5% of the maxmum values The resdual nclnatons after njecton 6C reman at about 3% of the maxmum wdth (whch was very large due to the hgh net pressure) The much larger resdual wdth after njecton 6C s

8 6 L NR WAlPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER due to the propped wdth of the fracture (about 35 n based on the maxmum fracture wdth predcted by FRACPROTM) Dscusson As ths seres of tests completes the MSte feld experments the man dagnostc objectve of valdatng the accuracy and relablty of the mcrosesmc method has been acheved By usng the array of nclnometers ntersectngwell nformaton and much other data t s clear that n formatons where mcrosesmc actvty s nduced by a hydraulc fracture a map of ths actvty provdes a relable mage of the fracture The C sand experments had as ther prmary dagnostc objectve the determnaton of the accuracy of the mcrosesmc length through a correlaton of the maged data wth the ntersecton of a lateral wellbore Ths ntersecton was acheved on the 2C njecton and showed that the maged length was correct wthn the accuracy lmts of the technque Prevous MSte result^'^ had shown that mcrosesmc heghts and azmuths were also correct wthn ther accuracy lmts n addton the fracture azmuth was found to closely agree wth the prevously determned stress orentaton" Whle the prmary purpose of the nclnometer array (downhole tltmeter array) was to provde valdaton of the mcrosesmc results by measurng the mechancal response of the rock to the hydraulc fracture t was also found that the nclnometers can be a very useful tool for fracture dagnostcs n addton to the accurate heght measurements the nclnometer array has been found to be valuable for determnng the resdual wdth of the fractures and the fnal propped wdth dstrbuton relatve to the orgnal fracture wdth dstrbuton n addton the nclnometer s a very precse nstrument for measurng fracture openng and thus closure stress These tests along wth prevous results" have shown that the fracture heght determned by models s not partcularly accurate There are clearly many addtonal mechansms affectng heght growth that have not been ncorporated adequately nto models Dagnostc results such as these can be used to ad n mprovng the model capabltes The seres of tests usng both lnear and crosslnked gels also shows that there s a sgnfcant vscosty effect Comparng treatments C and 2C t s found that the lneargel fracture resulted n % more lengh growth for only 4% more flud even though there was hgher leakoff of the lnear gel Comparng treatments 3C and 5C t was found that comparable len&s were obtaned for both treatments even though the crosslnked gel had twce the flud volume Whle tp effects may stll be mportant n fracturng t s clear that vscosty has an mportant role n fracture extenson n partcular thnflud fractures acheve fast length extenson wth lttle heght growth a feature that could be used wth great advantage to optmze fracturng procedures On the other hand t s not clear why such dfferent behavor was not always reflected n the net pressure Agan t appears that there are some elements of fracturng that are not entrely understood Dagnostc results such as these can provde valuable data to mprove model results The experments have also demonstrated that the mcrosesmc method s accurate for measurng largescale complexty n fracture treatments Whle smallscale complextes such as multple parallel strands cannot be the large scale complextes such as secondary fractures and horzontal fractures are readly apparent (eg njecton 6C) t s also noteworthy that the secondary vertcal fractures occurred after the njecton pressure exceeded the maxmum horzontal stress and the horzontal features occurred after the pressure exceeded the overburden stress The measurement of resdual fracture deformaton by the nclnometers offers mportant nsght nto the successful mplementaton of water fractures (no prop) The large resdual deformatons nterpreted as fracture wdth shows that sgnfcant wdths can reman even wthout proppant The nterpretaton of the resdual deformaton as wdth s due to the careful montorng of reservor pressure to ascertan that the effect s not due to poroelastc behavor Although the effect could be due to anelastc behavor we hope that ths s not the case as t would nvaldate all fracture models reservor mechancs models tltmeter analyses stress logs and many other calculatons whch requre elastc behavor of the reservor The nclnometers have also been used for determnng changes n the proppant dstrbuton an mportant element for evaluatng convecton and prop transport n the two experments at MSte lttle ndcaton of dropout or convecton has been observed Wth regard to fracture models these dagnostc technques cannot provde detals on fracture mechansms (eg multple fractures tp effects fssure openng etc) but the overall mage of the fracture does allow for accurate testng of model accuracy n gven reservors t s expected that such results wll requre modelers to reexamne the mplementaton of many mechansms related to heght growth net pressure and prop transport Models are mportant elements n any fracturng desgxdanalyss program and any mprovements n models based on magng wll pay valuable dvdends n both hydrocarbon recovery and economcs Fnally the value of magng technology should be readly apparent to all companes nvolved n fracturng reservors t can provde mmedate benefts n desgnng the well layout for new felds and nfll operatons for the optmzaton of multzone completons and for the evaluaton of problem reservors Conclusons Hydraulcfracture magng usng the mcrosesmc method has been shown to be an accurate technque for montorng fracture growth and determnng the fmal sze and shape of the

9 MCROSESMC AND DEFORMATON MAGNG OF HYDRAULC FRACTURE GROWTH AND GEOMETRY _ fracture Fracture length heght and azmuth have been valdated usng other technology at MSte An nclnometer array (downhole tltmeter array) has been found to provde mportant nformaton on fracture parameters not readly measured usng mcrosesms or other avalable dagnostc nformaton Kew features measured nclude resdual wdths fnal prop placement and closure stress Results at MSte show that fracture heght s much more complcated than currently mplemented n models and that vscosty has a sgnfcant effect on fracture growth n addton these feld results provde proof of complex fracture growth when pressures exceed the maxmum horzontal or the overburden stress values As magng results become more wdely avalable and are ncorporated nto model enhancements hydraulcfracture optmzaton should mprove accordngly These dagnostc technques should be of value for new felds nfll drllng programs multzone completons and any problem reservors Nomenclature horzontal dstance to source L ft elevaton of source L ft t= tme of mcrosesm orgnaton t sec Vp= pwave velocty L/t Wsec Vs = swave velocty Llt Wsec z = elevaton of recever L ft fpl= pwave arrval tme at * recever t sec r s p swave arrval tme at the recever t sec F F Acknowledgments These experments were conducted under fundng by the Gas Research nsttute managed by Steve Wolhart and by the Department of Energy managed by Jm Ammer at FETC The authors would lke to acknowledge the support provded by both Steve and Jm and would lke to thank Dck Myal and Rob Zes of CER Corporaton for ther dedcated help BOLT Technology Corp for ther feldng of the multlevel wrelne recever array and the many servce companes nvolved n these tests References Warpnsk NR Moschovds ZA Parker CD and AbouSayed S (994) Comparson study of hydraulc fracturng models test case: GR staged feld experment 3 SPE Producton & Facltes Warpnsk NR Lorenz JC Branagan PT Myal FR and Gall BL: Examnaton of a Cored Hydraulc Fracture n a Deep Gas Well SPE Producton & Facltes August 993 Fast RE Murer AS and Tmmer RS: Descrpton and Analyss of Cored Hydraulc Fractures Lost Hlls Feld Kern County Calforna SPE th Annual Techncal Conference & Exhbton Washngton DC: l Branagan PT Peterson R Warpnsk NR and Wrght TB The Characterzaton of Remotely ntersected Set of Hydraulc 7 Fractures: Results of ntersecton Well No : GRDOE MultSte Project SPE SPE Annual Tech Conf gl Exh Denver CO Oct Warpnsk NR and Teufel LW: nfluence of Geologc Dscontnutes on Hydraulc Fracture Propagaton JPT Feb Warpnsk NR: Measurement of Wdth and Pressure n a Propagatng Hydraulc Fracture S P W 46 February Jeffrey RG Brynes RP Lynch PA and Lng DJ: An Analyss of Hydraulc Fracture and Mneback Data for a Treatment n the German Creek Coal Seam paper SPE SPE Rocky Mountan Regonal Mtg Casper WY Jeffrey RG Enever JR Ferguson T Brde J Phllps R and Davdson S: SmallScale Hydraulc Fracturng and Mneback Experments n Coal Seams paper ntern atonal Coalbed Methane Symposum U of Alabama Tuscaloosa 9 Jeffrey RG Settar A and Smth NP: A Comparson of Hydraulc Fracture Feld Experments ncludng Mneback Geometry Data wth Numercal Fracture Model Smulatons paper SPE 358 SPE Annual Techncal Conference & Exhbton Dallas TX Albrght JN and Pearson CF Acoustc Emssons as a Tool for Hydraulc Fracture Locaton: Experence at the Fenton Hl Hot Dry Rock Ste SPEJ August Vnegar HJ et al Actve and Passve Sesmc magng of a Hydraulc Fracture n Datomte JPT Jan Truby LS Keck RG and Wthers RJ Data Gatherng for a Comprehensve Hydraulc Fracture Dagnostc Project: A Case Study paper SPE 2756 proc 994 ADC/SPE Drllng Conf Dallas TX Feb 58 3 Peterson R et a Results of MultStes Expermentaton n the A Sand nterval: Fracture Dagnostcs Fracture Modelng and Crosswell Tomography GR Topcal Report GR95/66 Aprl Warpnsk NR Engler BP Young CJ Peterson R Branagan PT and Fx JE (995) Mcrosesmc mappng of hydraulc fractures usng multlevel wrelne recevers Paper SPE 357 SPE Annual Techncal Conference and Exhbton Dallas TX A Warpnsk NR Wrght TB Uhl JE Engler BP Drozda PM and Peterson RE (996) Mcrosesmc montorng of the Bsand hydraulc fracture experment at the DOE/GR MultSte project SPE SPE Annual Techncal Conference & Exhbton Denver CO A Wrght CA and ConanL RA (995) Hydraulc fracture reorentaton n prmary and secondary recovery from low permeablty reservors SPE 3484 SPE Annual Techncal Conference & Exhbton Dallas TX ll Peterson RE Wolhart SL Frohne KH Warpnsk NR Branagan PT and Wrght TB Fracture Dagnostcs Research at the GRLDOE MultSte Project: Overvew of the Concept and Results SPE proc SPE Annual Tech Conf and Exh Denver CO Oct Mddlebrook M Peterson R Warpnsk NR Engler B Sleefe G Cleary M Wrghht T and Branagan P MultSte Project Sesmc Verfcaton Experment and Assessment of Ste Sutablty GR Topcal Report GR93/5 Feb Sleefe GE Warpnsk NR and Engler BP The Use of Broadband Mcrosesms for Hydraulc Fracture Mappng SPE

10 8 NR WARPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER Formaton Evaluaton Drc Mwx3 Branagan PT Warpnsk NR Engler BP Wlmer R "Measurng the Hydraulc Fracturenduced Deformaton of Reservor and Adjacent Rocks Employng a Deeply Bured nclnometer Array: GRDOE MultSte Project'' SPE 3645 SPE Annual Tech Conf & Exh Denver CO Oct Branagan PT Peterson RE Warpnsk NR Wolhart SL and Hll RE: "Propasaton of a Hydraulc Fracture nto a Remote Observaton Wellbore: Results of Csand Expermentaton at the GR/DOE MSte Project" SPE SPE Annual Techncal Conference & Exhbton San Antono October England AH and Green AE (963) Some twodmensonal punch and crack problems n classcal elastcty Proceedngs Cumbrdge Phlosophcal Socety Green AE and Sneddon N (95) The dstrbuton of stress n the neghbourhood of a fat ellptcal crack n an elastc sold Proceedngs Cambrdge Phlosophcal Socety Warpnsk NR and Teufel LW "n stu Stresses n LowPermeablty Nonmarne Rocks" JPT Aprl Warpnsk NR "nterpretaton of Hydraulc Fracture Mappng Experments" paper SPE proc Tulsa Centennal Petroleum Engneerng Symp Tulsa OK Aug n MULTLEVEL &?RELNE RECEVERS E+OO = cm E = m3 E+OO = N E+OO = kpa E+OO = m3/s E3 = m3 MONTOR 8 *L * PRESSURE / m m O R RECEWERS c ACCELEROMETERS 4Z m m rn Fgure 2 Layout of MSte wells and nstrumentaton GAMMA RAY (AP UNTS) S Metrc Converson Factors f x 348* E = m n x 254* bbl x LB x ps x bpm x gal x [ SPE E A 43 n 435 k Q W Fgure 3 Gamma ray log showng C sand lthology n E Fgure Pan vew of MSte STRESS (ps) C SAND 5 Fgure 4 Stress contrasts around C sand B SAND TLTMETERS

11 MCROSESMC AND DEFORMATON MAGNG OF HYDWULC FRACTURE GROWTH AND GEOMETRY 6 9 ~ AFTER 5 MN 5 MWXJ 45 h v) P 4 U!Y 3 m 35 MONTOR U 3 y b \ 25 c 2 6cPROPPED SC: MAGNOSTlC TME (mn) : n 3 2 WESTEAST (ft) MWXZ ~ 42 L w MONTOR AFTER5MN Fgure 5 Correlated pressure data for C sand njectons 2 CLWR!Y n u) * *** **e< CSAND m MWX3 ' ALONG FRACTURE LENGTH (ft) Fgure 7 njecton C mcrosesms after 5 mnutes (shut n) 6w z AT NTERSECTON m Mwx3 ml 3 2 MONTOR WESTEAST (ft) 2 3 awx2 42 ' a MONTOR 3 2w loo 2 WESTEAST (ft) 4 Mwxz 3 43 ATNTERSECTON! NTERSECTONWELL 4m E MONTOR a ALONG FRACTURE LENGTH (ft) Fgure 6 All njecton C mcrosesms t 2 3 n w n / ** 44 MCUTOR SLWR ALONG FRACTURE LENGTH (ft) Fgure 8 njecton 2C mcrosesms at ntersecton 4 5

12 NR WARPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER so4 MWXJ 2 :T5 < E MONTOR ! 3 4 Mwx2 42 m loo WESTEAST (ft) z_ E e * * ( ' l 23 * 235 n ' L TME (day of the year) Fgure Long term nclnatons after unproppedfractures 4 8 NTERSECTONWELL ' 44 j 6 N74W E= 4 ALONG FRACTURE LENGTH (R) AFTER 3 MN MWX3 5 F Fgure 9 All njecton 2C mcrosesms 3 3 Y z 8 MWX3 z 2 MONTOR WELL WESTEAST (ft) wa MONTOR 5 ~ 3 2 w loo WESTEAST (R) 2w 2 43 Mwxz j *** AFTER 3 MN MWX2 3 ALONG FRACTURE LENGTH (ft) 5 Fgure 2lnjecton 4C mcrosesmc mage pror to restart 45' 5M w 2 m ALONG FRACTURE LENGTH (ft) Fg O All njecton 3C mcrosesms 4 5w 7

13 MCROSESMC AND DEFORMATON MAGNG OF HYDRAULC FRACTURE GROWTH AND GEOMETRY _ SPE m! m MWX3 N74W FRAC 5C MWX MWX2 2 MONTCf ~~ v) w 3w MWXZ 42 FRAC 5C 4mt 3 J 3 3 MWTOF~ ALONG FRAC LENGTH (ft) Fgure 5 All njecton 5C mcrosesms MWX WESTEAST (ft) 4 WESTEAST (ft) 4 5 j MONTOR WELL MONTORWELL ALONG FRACTURE LENGTH (ft) 6 AFTER 5 MN Fgure 3 All njecton 4C mcrosesms sl m FRAC 6C MWXd 4 2n W sb~~ 4 2 w 42 5 A C Sandstone 44! W 46 MWX2 MONTORWELL 7 5 Joo m DSTANCE ALONG FRACTURE (R) 3 5 4W B H=37 48 ft NCLNATON (Mcroradans) Fgure 4 njecton 4C nclnaton results (2D Fnte Element) 42W 25 44cK 4 4 2w 4 6 DSTANCE ALONG FRACTURE (ft) Fgure 6 njecton 6C mcrosesms after 5 mnutes of njecton

14 NR WARPNSK PT BRANAGAN RE PETERSON JE FX JE UHL BP ENGLER R WLMER g l W t ** CLWa * MONTOR WELL 3w C DSTANCE ALONG FRACTURE (ft) * f 5 5 NORMALZED NCLNATONS 4 Fgure 9 nclnaton dstrbuton through closure 42 " E n w n zw 4 2 DSTANCE ALONG FRACTURE (ft) 4 6 2! 4 E Fgure 7 All njecton 6C mcrosesms 5 v) d 6 8 oo W TME (day of the year) Fgure 2 Longterm nclnatons after 4C and 6C treatments MWX2 h DSTANCE FROM FRAC PLANE (ft) Fgure 8 Edgeon vew of all 6C mcrosesms 3 365