Task

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1 Task 9.0 Phase I Interim Reprt Lwering Drilling Cst, Imprving Operatinal Safety, and Reducing Envirnmental Impact thrugh Znal Islatin Imprvements fr Hrizntal Wells Drilled in the Marcellus Shale Date Jeff Watters, Principal Investigatr General Manager CSI Technlgies 2202 Oil Center Curt Hustn TX, 77073

2 LEGAL NOTICE This reprt was prepared by CSI Technlgies LLC as an accunt f wrk spnsred by the Research Partnership t Secure Energy fr America, RPSEA. Neither RPSEA members f RPSEA, the Natinal Energy Technlgy Labratry, the U.S. Department f Energy, nr any persn acting n behalf f any f the entities: a. MAKES ANY WARRANTY OR REPRESENTATION, EXPRESS OR IMPLIED WITH RESPECT TO ACCURACY, COMPLETENESS, OR USEFULNESS OF THE INFORMATION CONTAINED IN THIS DOCUMENT, OR THAT THE USE OF ANY INFORMATION, APPARATUS, METHOD, OR PROCESS DISCLOSED IN THIS DOCUMENT MAY NOT INFRINGE PRIVATELY OWNED RIGHTS, OR b. ASSUMES ANY LIABILITY WITH RESPECT TO THE USE OF, OR FOR ANY AND ALL DAMAGES RESULTING FROM THE USE OF, ANY INFORMATION, APPARATUS, METHOD, OR PROCESS DISCLOSED IN THIS DOCUMENT. THIS IS AN INTERIM REPORT. THEREFORE, ANY DATA, CALCULATIONS, OR CONCLUSIONS REPORTED HEREIN SHOULD BE TREATED AS PRELIMINARY. REFERENCE TO TRADE NAMES OR SPECIFIC COMMERCIAL PRODUCTS, COMMODITIES, OR SERVICES IN THIS REPORT DOES NOT REPRESENT OR CONSTIITUTE AND ENDORSEMENT, RECOMMENDATION, OR FAVORING BY RPSEA OR ITS CONTRACTORS OF THE SPECIFIC COMMERCIAL PRODUCT, COMMODITY, OR SERVICE. i

3 Abstract This lng term cmprehensive study f the cement systems and field peratins applied in the Marcellus Shale play targets eliminatin f znal islatin prblems and assciated cst, safety, and envirnmental issues. The apprach is t develp an integrated prcess t ptimize znal islatin, reduce jb prblems, minimize remedial cementing, and ptimize rig time spent waiting n cement. In this n ging study, a systematic and hlistic apprach was taken t analyze and ptentially imprve cementing peratins n all casing strings. Initially, a methd f bservatin and analysis is develped using labratry testing, field bservatin and engineering analysis. This methd allws fr identificatin f issues r gd practices. Frm issues identified, recmmendatins can be made. Once a set f recmmendatins are agreed upn, practices can be implemented. The imprvements d nt stp here, as this prject prgresses, a cnstant feedback lp will be cntinuusly running with new ideas t imprve cementing technlgy and peratins. This prject is in the stage f making recmmendatins; hwever initial results and data frm similar prjects indicate that by fcusing n cementing peratins and design leads t an verall increase in the quality f cementing prcesses. Cnsidering the current emphasis n U.S. shale drilling and evidence f imprvement frm previus research 1 cementing imprvement delivers ptential fr reduced cst and increased safety. Imprved cement perfrmance prduces better znal islatin which can result in lwer cst t drill, mre effective fracturing peratins, and higher ultimate prductivity f the well. This prject was specifically chsen by RPSEA t identify issues in shale and identify best practices that will alleviate issues with znal islatin, safety and the envirnment in shale reservirs. ii

4 Signature and Date Stamp X Jeff Watters Principal Investigatr Date iii

5 THIS PAGE INTENTIONALLY LEFT BLANK iv

6 Acknwledgement Statement CSI Technlgies wishes t acknwledge the supprt f RPSEA, Chesapeake Energy and the University f Hustn fr their invaluable expertise and cntributins made tward this prject. v

7 Nmenclature: bbl: Barrel BHCT: Bttm Hle Circulating Temperature BHP: Bttm Hle Pressure BHST: Bttm Hle Static Temperature BOP: bpm: ECD: ID: MD: OD: ppg: PV: Blw Out Preventer Barrels per minute Equivalent Circulating Density Inner Diameter Measured Depth Outer Diameter Punds per galln Plastic Viscsity SGSA: Static Gel Strength Analyzer TOC: TOL: UCA: Tp f Cement Tp f Liner Ultrasnic Cement Analyzer WOC: Wait n Cement YP: Yield Pint vi

8 Cntents Lwering Drilling Cst, Imprving Operatinal Safety, and Reducing Envirnmental Impact thrugh Znal Islatin Imprvements fr Hrizntal Wells Drilled in the Marcellus Shale... i Abstract... ii Acknwledgement Statement... v Nmenclature:... vi 1 Executive Summary Prject Intrductin Marcellus Shale Backgrund Infrmatin Expected Prject Challenges Prject Apprach Assess Chesapeake s Cementing Operatins in the Marcellus Shale Review and Dcument Current Cementing Operatins Observe Drilling and Cmpletin Operatins Run State f the Art Bnd lg Suites Analyze Causes f Cementing Failures and Methds t Prevent Failures Cnduct Labratry Investigatin Cement Cmpsitin Design Gas Flw Placement Methds and Slurry Stability Additinal Specialized Testing Shrinkage and Expansin Rings Impact testing Mechanical prperties testing Tensile Testing Specify Apprpriate Cementing Techniques t Address Issues Identified Operatins Cement Design vii

9 6 Develp Field Analytical Methds t Quantify Ptential fr a Cementing Issue t Occur n a Particular Well Assess Well Drilling Cnditins Develp Rutines t prepare fr effective cementing Technlgy Transfer Activities Path Frward Table f figures, equatins, charts and tables Figure 1: Stages f gas migratin... 5 Figure 2: Prject Prcess... 8 Figure 3: Typical well design studied in this prject... 9 Figure 4: Testing prcedure fr gas migratin ptential Figure 5: Shwing an impact test being perfrmed as well as the fractured sample pst test Figure 6: Diagram f tensile test Equatin 1: Tensile strength equatin Chart 1: Cmparing success rate f Service cmpany A vs Service Cmpany B fr the first phase f the prject Chart 2: Imprtance f variables in statistical analysis Chart 3: Expansin f set cement at intermediate cementing cnditins Chart 4: Average number f impacts required t fracture a bar sample after 24 hurs f cure time Chart 5: Tensile strength results Table 1: Cement bnd lg analysis fr histrical Data. Well name crrespnds t wells analyzed in Appendix 1B Table 2: Cement bnd lg analysis fr real time data. Well name crrespnds t wells analyzed in Appendix 1C Table 3: Variables investigated in statistical analysis Table 4: Cmpsitin f surface and intermediate systems Table 5: Cmpsitin f prductin cement systems Table 6: Cement system transitin times and gas migratin ptential at surface and intermediate cnditins Table 7: Mechanical prperties results viii

10 1 Executive Summary This reprt is submitted in fulfillment f Task 9 f the Lwering Drilling Cst, Imprving Operatinal Safety, and Reducing Envirnmental Impact thrugh Znal Islatin Imprvements fr Hrizntal Wells Drilled in the Marcellus Shale prject and cntains a summary f Phase I activities, identificatin f technical issues and peratinal practices that shuld be addressed t imprve znal islatin, and a recmmended path frward t implement said practices. Phase I f this prject has fcused n dcumenting the current status f technlgies thrugh literature investigatins, labratry testing, field bservatins and engineering analysis. This phase als aimed t establish best practices fr cementing in the Marcellus shale play. The bjectives f phase I tasks have been t determine and evaluate current practices and t analyze the results. Once analyzed, best practices are determined and used in the phase II implementatin stage. Anticipated challenges when implementing these practices are reaching the entire field and ffice staff f the Marcellus shale and reaching cmpanies utside f this prject. All aspects f wells drilled and cemented in the Marcellus shale play frm January 2012 t December 2012 were evaluated. This evaluatin cvered everything frm drilling t pst cementing well perfrmance. This started with a histrical data investigatin. Twenty wells drilled frm January May 2012 were evaluated with a fcus n the cement jbs. There was ne cement jb perfrmed fr each f the surface casing, intermediate casing and prductin casing n each f these wells, resulting in a ttal f 60 cement jbs. Next, t bserve actual cement jbs, a field representative was sent t Pennsylvania and ver the curse f 5 mnths, bserved an additinal 60 cement jbs t see peratins first hand. After bservatin, bnd lgs and perfrmance data were prvided fr wells bserved. Data cllected frm this stage was used t analyze and determine any peratinal causes fr ptential pr znal islatin. During cement jb bservatins, field persnnel cllected and shipped cement blend and lcatin water samples t the CSI labratry fr further testing and analysis. Testing was perfrmed n these field blend samples as well as pilt samples f cement and additives. Initially, typical ilfield cement testing was perfrmed n each system. After establishing sme baseline parameters, specialized testing was used t further analyze the cement systems. During this stage, several parameters were identified that had nt been included in the prjected plan. In rder t investigate these parameters, several tests were develped t quantify and evaluate the cement systems. The data cllected frm well evaluatin and labratry testing was analyzed and used t develp a methd f quantifying ptential fr a znal islatin failure t ccur n a particular well. By statistically analyzing each well, a methd was develped in rder t determine with a certain level f cnfidence a well that wuld have successful znal islatin. Frm these 2

11 results, a decisin matrix was made t assist engineers and field persnnel in decisins invlving cementing and drilling. The results f phase I indicate ptential issues with cement systems being used as well as sme cementing prtcls. This resulted in an additinal time perid f 6 mnths added t the prject as well as additinal labratry testing t prvide additinal infrmatin. These results were crrelated t field wrk and used t help determine the practices and cement systems t be implemented. 2 Prject Intrductin The bjective f this prject is t undertake a systematic and cmprehensive study f the cementing prcess applied in the Marcellus shale, targeting deficits and identifying recmmendatins that can be made t allw fr imprvement. These imprvements will be dcumented alng with the resulting effects n safety, znal islatin, envirnmental issues and verall cst fr the peratr. This systematic apprach t cllecting and analyzing data sets, identifying deficits, making recmmendatins and implementing changes can be used in any shale area t imprve peratins and increase technlgy. 2.1 Marcellus Shale Backgrund Infrmatin The Marcellus frmatin is Middle Devnian and cvers an area abut 95,000mi 2. This frmatin cnsists primarily f black shale with smaller amunts f bentnite, limestne, and siltstne. The frmatins abve the Marcellus cnsist f sandstne, limestne, ther varius shales, as well as pckets f shallw gas frmatins. It is estimated this area cntains 200 tcf (Dittrick) f recverable natural gas, with an estimated 84 tcf (J.L. Cleman) f undiscvered natural gas. Currently, mst develpment is lcated in Pennsylvania. The depth f the Marcellus frmatin in this area ranges frm 4,000 9,000, with a thickness f ft (J.L. Cleman). The majrity f wells are hrizntal, with the hrizntal lateral extending 2,000 6,000' in length (Anthny Jnes). Accrding t the Pennsylvania Department f Envirnmental Prtectin 1,213 ut f 1,405 wells spudded in the Marcellus in 2010 were hrizntal. Hrizntal wells and advances in stimulatin have allwed shale wells t becme ecnmical since hrizntal wells increase the area expsed t the prducing frmatin with a minimized surface ftprint. A recent study by Pennsylvania State University estimates that the Marcellus culd result in 256,420 jbs and add $20 billin t the state ecnmy (Dittrick). Drilling and cmpleting shale gas wells is a technically cmplex peratin that can present many challenges. The thusands f feet f lateral may result in cuttings and mud slids settling ut n the lw side, resulting in mud remval issues. Als, the peratr needs t place cement thrugh this lng, lateral sectin and the cement must remain pumpable while still retaining the ability t develp adequate cmpressive strength fr pst cementing peratins. During 3

12 cementing, slurry design and placement may ultimately impact znal islatin. Cmplete znal islatin is desired in every well. Addressing deficiencies with the cement slurry and peratins befre the cement jb will ensure prper techniques and systems are in place, and will reduce verall csts as well as imprve safety during rig peratins, and decrease the pssibility f envirnmental cncerns (Jessica Bassett) (Phillips). Cncerns ver the envirnment and safety have increased with the grwth f well peratins in the Marcellus. These cncerns include well cntrl, grundwater cntaminatin, chemical use, waste dispsal, water usage and the prximity f drilling and stimulatin t urban areas (Huls). Additinally, the lifetime f a well in an uncnventinal reservir may be much lnger than that f a cnventinal well, leaving mre time fr crrsin t take place (Miskimins). Hrizntal wells may be mre susceptible t crrsin if the primary cement jb is nt adequate. Cement in the annulus between the frmatin and the casing prvides supprt t the casing strings, prvides znal islatin between frmatins and prtects grundwater frm cntaminatin. If cement integrity is cmprmised in a gas well, pathways fr shrt and lng term gas migratin can be created and annular leaks between znes may ccur. This lss f znal islatin can lead t sustained casing pressure and, in severe cases, lss f well cntrl r blwuts. Well cst is als increased due t the high cst f remedial wrk (Rbert Brks) (US Department f Energy). 2.2 Expected Prject Challenges A review f past literature n the current practices in the Marcellus shale has shwn that the fllwing challenges apply: Drilling cnsideratins Stability: When expsed t water, shales can swell r delaminate, causing tight hle cnditins r hle cllapse. Shale swelling can cause prblems during drilling, running casing and during cementing peratins and is estimated t be respnsible fr up t 70% f drilling prblems. Sme fluids have been develped specifically fr use in the Marcellus shales. Use f an il r synthetic based mud r an inverse emulsin fr inhibitin has been shwn t reduce stuck pipe and imprve hle cleaning. Incmplete hle cleaning can lead t lst circulatin, issues during cementing and pr bnding. Factry Drilling: A prcess in which the peratr repeatedly drills a high number f standardized wells in rder t lwer cst and reduce verall cst per well. This methd wrks very well in shale areas where the frmatin is hmgenus and dwnhle cnditins are knwn. This methd can reduce time and mney spent per well in a field. Hwever, the ne pitfall is prductin f individual wells may nt be ptimized by this ne size fits all apprach. Applicatin f a standardized design may fail t 4

13 identify certain characteristics which culd affect lng term durability f the well, ne example being pckets f shallw gas. Mechanical Barriers: Znal islatin can be achieved thrugh the use f mechanical barriers such as packers. Inflatable Packers: Inflatable annular packerss are cmmnly used. This type f packer is attached t the casing string befre it is run dwnhle and is set hydraulically by annular fluids r cement slurry. The packer will thenn unifrmly expand t a certain OD t fill the annulus. Mechanical/Hydraulic set packers: Mechanical set packers are set thrugh tensin, cmpressin r rtatin f casing r drill string. Failure mdes f packers include peratinal prblems while running and mechanical failure during setting. If the hle is nt gauged, r if the casing is ffset, the packer may nt seal evenly and may nt frm a cmplete seal. Swellable packers: Swellable elastmer packers will swell t fill the annulus ver time when expsed t wellbre fluids. Depending n the packer design, it can take days fr the swellable packer t cmpletely seal thee annulus. They will keep expanding up t 200% f their size, until the annulus is filled. Cmmnly used fluids t swell the packers are hydrcarbn liquids r water, which can be damaging t shale frmatins. Sme ther drawbackcs t these packers, is that the Marcelluss has dry gas, resulting in a lw likelihd that a hydrcarbn swelling packer will encunter enugh hydrcarbn t swell t the pint f prviding an effectivee seal. Anther cncernn is the lng term durability, the material prperties f the rubber elastmer may change ver time, becming sfter and less able t prvide an effective seal. Lss f znal islatin: Cementing the annulus between the casing and frmatin prvides znal islatin as well as supprt fr the casing. Znal islatin prevents the flw f fluids frm ne frmatin t anther, this can present itself as gas migratin in a well wheree there are shallw gas znes. Znal islatin lss can ccur thrugh the cement itself r at the cement/casing r cement/frmatin interfaces. This lss can ccur inn the shrt term r lng term time perid. Gas migrating thugh slurry matrix Gas migrating thugh channels and micr annulus Shrt Term Lng Term Figure 1: Stages f gas migratin 5

14 Shrt term znal islatin lss ccurs if the hydrstatic pressure f the cement clumn becmes less than frmatin pre pressure while setting. During this time, gas frm the frmatin can enter the slurry and migrate up thrugh the matrix, ptentially leading t permanent pathways. Lng term znal islatin lss ccurs after the cement has set and can begin years after the well is cemented. Causes fr this type f lss can be due t pr mud remval, excessive channeling in the cement sheath, cntinued peratins causing cyclic stressing n the cement sheath and wellbre stresses due t tectnic stresses r temperature fluctuatin. Causes f znal islatin lss are utlined belw. Znal islatin lss can be related t: Mud remval: Cmplete displacement f mud prir t a cement jb is vital t allw the cement t prvide a seal fr adequate znal islatin. If mud remval is pr, leaving mud filter cake n the frmatin r leaving the casing il wet, this can destry any chances the cement had f bnding t either interface, resulting in little t n znal islatin. This lack f znal islatin can lead t fluids frm ne frmatin, flwing thrugh the wellbre and cntaminating upper frmatins. This pr znal islatin can als have a detrimental effect n cmpletins and prductin. Centralizatin: Centralizatin allws fr better mud remval. In lng hrizntal sectins it is vital t centralize the pipe as best as pssible. In any area where the flw is cnstricted, fluid, including cement slurry, will find the path f least resistance. In the case f an eccentric pipe, that means the wider side f the annulus will have cement cverage, leaving the narrw side with little t n cverage. By adding centralizers t the casing, fluids will flw arund the entire casing mre freely, resulting in better cement cverage. Cement Design: Cement design is a very imprtant part in imprving znal islatin. Varius cement prperties can be imprved upn that will help in this reductin. They are discussed belw: Cement Stability: T prvide adequate cement cverage, cement slurry needs t be hmgenus nce placed in the well. If the cement is unstable, it can result in little mre than water n the tp, and nearly all f the cement slids at the bttm. In a vertical well, this can reduce the hydrstatic pressure lcally, resulting in an influx f gas. In a hrizntal well, the prblems becme mre severe. In the Marcellus, the hrizntal sectin may be a few thusand feet lng, prgressing thrugh the frmatin. If the entire high side f that cement clumn is free water, there is n cement there t prvide znal islatin. That can result in fluid r gas migratin, reduced prductin, and difficulty perfrming fracturing jbs. Cement permeability: If a cement matrix is highly permeable, it can prvide a path fr gas t migrate ver time. With high permeability, the cement fails t prvide adequate znal islatin. A cement matrix may 6

15 als becme mre permeable as it ages. This can be due t chemical reactins happening within the cement r between the cement and ther chemicals present in the wellbre. An imprtant prperty f a cement sheath is t prvide adequate znal islatin fr the entire life f the well. Gel strength develpment: Hydrstatic pressure transmitted by a clumn f cement will decline as the cement develps gel strength and becmes self supprting. If the hydrstatic pressure f the cement clumn drps belw the frmatin pre pressure, gas frm the frmatin may enter the slurry and create pathways fr gas migratin, that may becme permanent. Transitin time is cnsidered t be the time that gel strength develps frm 100 lbf/100ft 2 t 500lbf/100ft 2. At 100lbf/100ft 2 gases are able t enter the cement slurry and begin migrating. At 500 lbf/100ft 2 gases are n lnger able t migrate thrugh the cement slurry. A slurry with higher gas migratin resistance, will have a shrter transitin time than a slurry with lwer gas migratin resistance. The shrter transitin time allws less gas t migrate t surface than a slurry with a lnger transitin time. Fluid Lss cntrl: Fluid lss cntrl is als imprtant in battling gas migratin. When a slurry lses a lt f fluid t the frmatin, it can lwer the hydrstatic pressure the slurry is able t exert n the frmatin. If this pressure is lwer than the pre pressure frm the frmatin, this can result in gas flw thrugh the cement matrix. Als, if the slurry is dehydrated against a zne and bridging ccurs, hydrstatic pressure belw that zne is reduced, which can als result in gas migratin. Cement Systems: Sme cement systems are specifically designed t cmbat gas flw. Certain additives are used t prevent shrt term gas migratin thrugh the cement matrix. Latex, plymer micrgels, and silica fume are amng sme f the additives used fr this. Thixtrpic cement slurries are anther ptin. They remain liquid as they are pumped, but when static will rapidly gain gel strength, this rapid transitin can reduce the risk f shrt term gas migratin. Anther system smetimes used is a gas generating cement. These systems use an aluminum pwder t create a cmpressible cement. The aluminum pwder reacts with water and prduces hydrgen gas bubbles dwn hle. The bubbles expand and exert pressure n the frmatin. When prperly designed, the hydrgen gas bubbles will remain interspersed thrughut the cement slurry alng the entire well. Anther aspect is cement durability. Mechanical prperties must be managed t allw fr gd znal islatin fr the life f the well. Tensile strength, Pssin s 7

16 rati, etc can indicate hw well a cement can withstand cyclic stresses frm drilling, fracturing, temperature, etc. 2.3 Prject Apprach Phase I f the prject has fcused n investigating the current practices and determining any specific techniques that culd be implemented t imprve znal islatin. The bjectives f the prject tasks in phase I have been t identify and develp best practices fr cementing in the Marcellus shale area and then estimate expected imprvements. T achieve this, all aspects f cement jbs were analyzed in a hlistic type apprach. This required cllecting data frm the field as well as labratry testing all t be included in engineering analysis. The methdlgy used in this prject was t analyze the data frm the field and labratry results. This analysis allwed fr the identificatin f any ptential deficits in the cement design r applicatin. Frm this, recmmendatins culd be made t help imprve the deficits seen in the field r labratry. After making recmmendatins, CSI will wrk with Chesapeake t develp a plan fr field implementatin f the recmmendatins t ensure they will be applied crrectly when necessary. During and after implementatin, CSI will cntinue t mnitr fr imprved results. The belw diagram shws a graphical representatin f the apprach fr this prject. Develp Methdlgy Identify Deficits Make Recmmendatins Implement Changes Imprved Results Figure 2: Prject Prcess 3 Assess Chesapeake s Cementing Operatins in the Marcellus Shale 3.1 Review and Dcument Current Cementing Operatins The first majr step in this prject was t determine hw the current cementing peratins were perfrmed and what particular fluids systems were being used. T d this, data was cllected frm wells drilled during the previus six mnths. This well data included: Drilling data 8

17 Mud systems Cement systems Well pathway Well perfrmance data Pst cementing peratins This data was cllected and analyzed by engineers and field specialists t identify any areas needing imprvement r best practices in use. In this task, 20 wells were analyzed, fr a ttal f 60 cement jbs. Of these 60 cement jbs, many included cement bnd lgs inn the data fr analysis. The interpretatin f the cement bnd lgs were crrelated t ther data gatheredd t determine cement perfrmance. A full summary and analysis f the data cllected is shwn in Appendix 1B fr the field data summary and analysis. Figure 3: Typical well design studied in this prject Figure 3 shws an example f the wells drilled in the Marcellus shale. These wells have an uncemented cnductr casing set at arund , a surface casing at 500 1,000 and an intermediate casing at 1,500 2,000. Within the intermediate casing, a prductin casing string is run, vertically t arund 7,000 and hrizntally ut t arund 13,000. As can be seen in the schematic, cement is run t surface 9

18 in all strings except the prductin string, were a small gap f abut 1,000 is left pen t the frmatin. The infrmatin cllected regarding these wells included cementing and drilling techniques as well as prperties f the cement and tls used in these wells. 3.2 Observe Drilling and Cmpletin Operatins After cllecting histrical data, field persnnel frm CSI were sent t Pennsylvania t bserve field peratins. One f the first steps when preparing fr a cement jb is t blend lad the dry cement at the bulk plant. This step is extremely imprtant fr the quality f cement jb relies heavily n the quality f the cement blend. Each blend must have the crrect rati f additives t cement in rder t allw the cement pump peratr t mix the cement slurry crrectly n a jb site. Field persnnel fr CSI bserved blending and lading peratins at the bulk plants t ensure the cement that went t lcatin was blended at the right cncentratins and as thrughly as pssible. This step was perfrmed using the prcess fr bulk plant audits described in Appendix 1A. After the cement is laded, it is sent t the well where it will be used. At this pint, the CSI field persnnel was als called t lcatin t bserve the rig up f the cementing equipment as well as precementing peratins perfrmed n the well. All peratins are recrded in the prvided audit frm. The prcess fllwed when filling ut this frm is detailed in Appendix 1A. The CSI persnnel recrded infrmatin frm the pint when the service cmpany rigged up t the pint when they began rigging dwn fr all cement jbs. During this time, CSI persnnel als cllected samples f blended cement and mixwater frm lcatin t be sent back t the CSI labratry. That audit sheet was sent back t CSI Technlgies ffices and used t determine any practices that lead t success r failure in the field. This data was used in cnjunctin with well perfrmance data and CBL data. The CBL was analyzed, and the interpretatin f that analysis was crrelated with field data t help determine cement perfrmance. The full summary and analysis f the data cllected is in Appendix 1C. 3.3 Run State f the Art Bnd lg Suites T determine the quality f cement after placement in a well, a cement bnd lg was run. Mst bnd lgs btained were frm the vertical sectin f the well, this cvered the surface and intermediate strings. Due t the nature f the tl, running a hrizntal bnd lg is much mre difficult. Hwever, 2 hrizntal bnd lgs were als run during this time. These bnd lgs were cllected and analyzed t determine the quality f cement that was placed. Fr intermediate sectins, 13 intermediate string cement bnd lgs were cllected and analyzed. The results f this analysis can be seen in table 1 belw. Thse results were crrelated with field results and lab results t begin t identify areas f imprvement. T analyze the cement bnd lg, the fllwing cut ffs were used in analyzing the casing and frmatin bnd 100 ft belw the she f the previus casing: 1 =best bnd <10mV n CBL 2 = mv 10

19 3= 20 40mV 4 = wrst bnd, >40mV n CBL Table 1: Cement bnd lg analysis fr histrical Data. Well name crrespnds t wells analyzed in Appendix 1B 100 ft cverage belw she Well Mix Water Date (Weather Name Casing Bttm Plug Packer Type Frmatin Bnd Temp, F Temperature) Bnd /10/12 NO Inflatable /2/12 NO N Packer /8/12 NO Inflatable /7/12 NO Inflatable /8/12 NO Inflatable /6/12 NO Inflatable /11/12 NO Inflatable /2/12 YES Swell /22/12 YES N Packer /8/12 NO Inflatable /12/12 NO Inflatable /8/12 NO Inflatable /20/12 YES Inflatable Table 2: Cement bnd lg analysis fr real time data. Well name crrespnds t wells analyzed in Appendix 1C Well Name 100 ft cverage belw she Mix Water Casing Bnd Frmatin Bnd Temp, F Date (Weather Temperature Bttm Plug Packer Type I 2 2 X Dec X X L /12/12 NO N Packer N /22/12 NO Inflatable P /2/12 NO Inflatable Q /6/12 NO Inflatable S 2 2 August f 2012 A /7/12 NO Inflatable B /11/12 NO Inflatable C /1/12 YES N Packer G /25/12 YES N Packer T /18/12 YES Inflatable U /10/12 YES N Packer W /20/12 YES N Packer X /19/12 NO Inflatable 11

20 Y /9/12 NO Inflatable AB /31/12 YES N Packer AC /12/12 YES N Packer AD /20/12 NO Inflatable AF 2 2 X Mid Oct 2012 X X AG 3 3 X Mid Aug 2012 X X 3.4 Analyze Causes f Cementing Failures and Methds t Prevent Failures In additin t cllecting field data, well perfrmance data was als cllected. This perfrmance data can indicate znal islatin success r failure. This data was crrelated with the data cllected regarding peratins, cement design, and well cnditins and parameters. In additin t the well perfrmance data, cement bnd lgs were analyzed and als cmpared t the peratins, design and cnditins t help identify patterns leading t success versus failure. In this study, ne pattern nticed was the success rate in ne service cmpany versus the ther, specifically fr the intermediate casing. In the cases where the system used fr the intermediate casing cement was pumped by Cmpany B, success rate was much lwer than when Cmpany A pumped the cement, as seen in Chart 1. This was investigated fr all strings, as the failures n the surface string were s lw, data frm that was incnclusive, als since prductin strings are pen t frmatin, the peratr preferred the study be fcused n intermediate strings % 90.00% 80.00% Percentage Success 70.00% 60.00% 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% Histrical Data Cnventinal Cement Thixtrpic Cement Service Cmpany A Service Cmpany B Chart 1: Cmparing success rate f Service cmpany A vs Service Cmpany B fr the first phase f the prject A specific methd used here was a Partial Least Square Discriminant analysis (PLS DA) perfrmed at the University f Hustn. Partial Least Square Discriminant analysis is an effective way t study systems with several variables. It is a statistical methd fr finding the relatin between predictr variables, such as cement additives and rhelgical prperties, and binary respnse variables. Based n the discriminant functinal analysis, ne is able t predict znal islatin success r failure with sme 12

21 accuracy. X and Y matrices were frmed using the cementingg data prvided and analysis was dne n intermediate and prductin casing data. Dimensinless parameters were btained frm riginal predictr variables. Each string was analyzed separately. The intermediate results are in Table 2 and Chart 2 belw. Table 3: Variables investigated in statistical analysis Chart 2: Imprtance f variables in statistical analysis In Table 2, the list details the crrelatin between annular pressure and certain dimensinless parameters. If the parameter is negatively crrelated, it cntributes t reduced annular pressure. If it is a psitive crrelatin, then it is cntributing t increased annular pressure. Chart 2 shws hw 13

22 imprtant each parameter is. This is based n a VIP, r variable imprtance fr prjectin, statistic, the higher that number the mre imprtance the parameter has n final utcme f the well. 4 Cnduct Labratry Investigatin 4.1 Cement Cmpsitin Design The first step in the labratry study was t determine the current cmpsitin and hw it perfrmed under nrmal test prcedures. This testing included Thickening time Cmpressive strength develpment Free water Fluid lss Rhelgy (surface and dwnhle) Measured density Settling tests All cement samples gathered in the field were tested in the labratry and a summary f the results were recrded, average results are in Appendix 2A and 2B. These results were used t analyze and cmpare the results t the expected results. Certain parameters, such as fluid lss, can be greatly affected by the quality f the blend, as well as small adjustments in the fluid lss additive as a result f an incnsistent blend r lack f chemical. During this prject, tw main service cmpanies are being used. The cement systems used by them are as seen in Tables 3 and 4. These tables shw API cement class and cncentratins in percent by weight f cement (%bwc) f varius additives. Table 4: Cmpsitin f surface and intermediate systems Service Cmpany A B Cement System Surface/ Intermediate 1 Surface/ Intermediate 2 Surface/ Intermediate 1 Surface/ Intermediate 2 Re Designed Surface/ Intermediate 3 Cement Type Class H Class H Class A Class A Class H Gypsum %bwc CaCl %bwc NaCl%bww 12 Retarder %bwc 0.3 Fluid Lss %bwc Suspensin aid %bwc Stablizer %bwc 0.5 Antifam %bwc

23 Dispersant %bwc Defamer %bwc De static %bwc 0.02 Table 5: Cmpsitin f prductin cement systems Service Cmpany A B Cement System Prductin Lead Prductin Tail Prductin Lead Prductin Tail Cement Type Class H Class H Class A Class A Gypsum %bwc 5 Pzzaln %bwc 5 KCL %bww 5 Retarder %bwc Fluid Lss %bwc Suspensin aid %bwc 0.1 Stablizer %bwc 0.2 Antifam %bwc Dispersant %bwc Defamer %bwc De static %bwc Gas Prducing %bwc 1.2 The majr difference in Service Cmpany A versus Service Cmpany B is the cmpsitin f the cement slurry. The rati f gypsum t cement as well as the class f cement used is where they differ the mst. Service Cmpany A is using class H cement with 3% gypsum. Service Cmpany B is using Class A cement and 100% gypsum. This means that the cement t gypsum rati is 1:1 fr Service Cmpany B. The majr difference between the surface/intermediate 1 and surface/intermediate 2 fr bth service cmpanies is system 2 is thixtrpic. These systems were put int use in September f 2012, these results may als be seen in Appendix 2B. The re designed surface/intermediate system used by cmpany B was made in respnse t reprted well perfrmance data (Chart 1). Results frm the new system are still being finalized, initial results are als in Appendix 2B 4.2 Gas Flw The first f the specialized tests perfrmed was gas flw. This was perfrmed n a fluid migratin analyzer. A fluid migratin analyzer has the ability t test ptential fr gas flw in a cement system in a scaled dwn manner. There are tw parts t this test, the fluid lss prtin and the gas migratin prtin. The tw parts simulate what is ccurring in the well bth befre the slurry begins t develp gel strength, and during the develpment f gel strength. The static gel strength develpment f a slurry must be tested prir t testing fr gas flw. This requires a static gel strength test t be perfrmed. There are currently three ptins available fr this test. 15

24 Chandler SGSA: The SGSA is run similarly t the standard ultrasnic cement analyzer. The static gel strength is determined by measuring the change in ultrasnic signal that is transmitted thrugh the cement sample as it cures. This has been prven empirically, thrugh many tests. This test is ne f the easiest t perate as it is run typically while a cmpressive strength test is running n an SGSA/UCA cmbinatin machine. The dwnside is it des nt ffer a way t cnditin the sample prir t testing gel strength. Any cnditining needs t be dne n pressurized cnsistmeter befre lading the sample. Rtating Paddle Cnsistmeter/Static Gel Strength Analyzer: This machine has a slurry cup with a rtating paddle inside. This can be prgrammed t cnditin the slurry t simulate placement befre measuring gel strength withut switching machines. After the cnditining cycle, machine switches t gel strength measurement. T measure gel strength, the paddle mves slwly thrugh the slurry as it is develping gel strength. The trque applied t the paddle is measured and cnverted t a gel strength measurement. Multiple Analysis Cement System II (MACS II): This machine perfrms static gel strength test n cement slurry samples. The cement is first cnditined t simulate cement placement in dwnhle cnditins. Then the instrument begins cllecting gel strength data. Unlike the previus 2 systems, the MACS II directly measures gel strength instead f inferring the gel strength frm anther reading. The fluid lss prtin f the testing begins by mixing the slurry accrding t API specificatins. Then, the slurry cnditined n an atmspheric cnsistmeter fr a predetermined time t simulate the slurry placement in the well. After cnditining, the slurry is pured int the gas migratin cell which is preheated t bttm hle circulating temperature and a backpressure is applied t the bttm f the slurry. Pressure is applied t the tp as slurry at an initial pressure which is determined by the well and cement jb cnditins. The differential between the tw pressures is equal t the scaled dwn differential pressure f actual well cnditins. (SPE 19522) This differential pressure squeezes the cement, simulating the fluid lss experienced in a well. During this stage, pressure is decreased at time specified by a crrelatin with the amunt f gel strength the cement is develping. When this appraches a zer pressure differential, the gas migratin prtin f the test is started. If there is little fluid lss cntrl in the cement system, the result may be t much dehydratin f the cement clumn resulting in gas migratin in the secnd prtin f the test. During the gas migratin prtin f the test, nitrgen gas is used t simulate gas bubbling thrugh the slurry. The rate and vlume f gas entering and exiting the slurry are recrded and frm thse, cupled with the gas permeability calculatin, it can be determined if the slurry has sufficient gas migratin cntrl r nt. In additin, if the permeability f the set cement is belw 0.2 md, the slurry is cnsidered a gd cement t prevent gas migratin. This is desirable in the areas with high ptential fr gas migratin Receives Gas Gas Cement cell Receives Fluid 16

25 Transitin Times fr Thixtrpic Cement Systems Table 6: Cement system transitin times and gas migratin ptential at surface and intermediate cnditins Service Cmpany A2 B2 B3 String Surface Intermediate Surface Intermediate Surface Intermediate 100 lb/100sqft (hr:mn) 1:23 1:37 2:11 1:51 1:09 1: lb/100sqft (hr:mn) 1:42 1:50 12:56 3:44 1:22 1:44 Ttal time (hr:mn) 0:19 0:13 10:45 1:53 0:13 0:10 Gas Migratin Ptential Passed Passed Passed Passed Nt Tested Nt Tested The thixtrpic systems tested shwed gd transitin times fr service cmpany A and service cmpany B s third system. Slurries with shrt transitin times are cnsidered t be resistant t gas migratin, reducing the amunt f time gas can enter a cement matrix and migrate t surface. These systems were tested with a MACSII machine. 4.3 Placement Methds and Slurry Stability Slurry stability in a dynamic and static state was studied using varius methds. The first methd t determine the static stability f a slurry is t measure the density f the tp, middle and bttm f cement cured under bttmhle temperature and pressure. If the variance between the tp and bttm is significant, that can translate t pr cement cverage in a well. If the sectin is vertical, the tp prtin will have very pr cmpressive strength and lw density. In a hrizntal sectin, the upper prtin may have a large amunt f free water, ptentially resulting in a channel and cement with lw cmpressive strength. This can impact fracturing peratins and final prductin. T measure dynamic stability, tw methds were used. The first methd is used t indicate whether there may be an issue r nt. This is t measure the tp, middle and bttm densities f a sample frm a thickening time test. Differences greater than 5 7% can indicate need fr mre testing. A mre stringent test is a dynamic settling test. This test uses the same equipment as a thickening time, but a different schedule. After ramping t temperature and pressure, the cement is cnditined fr anther 20 minutes. After initial cnditining, the mtr is turned ff fr 10 minutes, t simulate a shut dwn during a cement jb. The mtr is turned n again fr anther 10 minutes, then ff again. At the end f the last n ff cycle, the mtr is turned and the spike in cnsistency is recrded. The mtr is turned ff again, and machine is cled t remve the cement sample as quickly as pssible and measure the tp, middle and bttm densities. This test helps t indicate the ptential fr failure during a cement jb. If the settling is severe during this test, it can translate t catastrphic failure in the field. 4.4 Additinal Specialized Testing Thrugh this prject, CSI and Chesapeake were able t identify ideas and ptential issues that had nt been previusly included in the scpe f wrk. Once these were identified, the prcesses fr testing 17

26 them were develped and the systems were tested. Analyzing the results helped t identify trends and decide if any f the ptential issues identified culd be actually affecting znal islatin in these wells. Testing was perfrmed t identify any shrinkage r expansin f the cement, gel strength transitin time, mechanical prperties f the cement, impact resistance, tensile strength, and permeability f set cement Shrinkage and Expansin Rings A cement system must remain bnded t the casing and the frmatin in rder t maintain znal islatin. Shrinkage f the cement sheath can ccur in as little as a few days and begin t allw gas t flw. All systems were tested fr shrinkage and expansin. This test set up requires a ring mld and a curing chamber. This ring mld is filled with cement and allwed t cure fr several days. Each day, the mld is remved frm the chamber and measured. Measurements are recrded and cmpared t the riginal measurement t determine percentage expansin r shrinkage. As can be seen in Chart 3, all systems tested shwed expansin during the 14 day test. This expansin indicates the cement sheath cntinued t expand slightly upn placement and did nt shrink. The likelihd that the cement remained bnded t the casing and frmatin is very gd. Char three als shws sme cement systems that have a slight shrinkage near the beginning f the test. This is likely an issue with the measurement device r the testing apparatus rather than actual shrinkage. Overall, this system shws at least slight expansin indicating that there is n verall shrinkage ver time. Expansin f Set Cement at Intermediate Cementing Cnditins Percentage Expansin Day 1 Day 3 Day 6 Day 9 Day 13 Day 14 Service Cmpany A Trial 1 Service Cmpany A Trial 2 Service Cmpany B Trial 1 Service Cmpany B Trial 2 Service Cmpany B Redesign Chart 3: Expansin f set cement at intermediate cementing cnditins Impact testing Midway thrugh this prject, Chesapeake and CSI discussed the pssible culprits resulting in cmprmised znal islatin, specifically in the intermediate casing. One area f interest was pst cementing peratins. After cementing surface and intermediate casings, drilling cntinues within hurs. The questin was if this affects the integrity f the cement sheath. Since bth f the cement 18

27 systems have similar cmpressive strengths, it was decided a type f impact test shuld be run t determinee any differences. There were tw types f impact tests develped fr this prject. The first was a small impact test. This used a 6 lng 1 x1 cement bar that was placed n hlder and a 66 gram ball was drpped frm a height 9.25 abve the cement sample. The number f drps this cement sample was able t withstand withut breaking was recrded. These tests were perfrmed after curing the cement fr 24 hurs. These results weree cmpared between cement systemss and the average results are shwn in Chart 4. As can be seen in the chart, thee system with less gypsum perfrmed better than the system with 100% gypsum. Figure 5: Shwing an impact test being perfrmed as well as the fractured sample pst test % Gypsum 100% Gypsum 5% Gypsum 1 0 Average Number f Impacts Chart 4: Average number f impacts required t fracture a bar sample after 24 hurs f cure time Mechanical prperties testing Mechanical prperties f cement can vary frm ne system t the next. In this prject, the mechanical prperties were crrelated t the perfrmance f the cement system in the labratry setting as well as t the perfrmance f the actual well these cement systems were being used n. These systems were tested fr ultimate cmpressive strength, Pssin s rati, andd Yung s Mdulus. Each f these results was cmpared fr the different systems. As seen in Table 6, Service Cmpany A s intermediate system perfrmed better than Service Cmpany B s system. This is likely due t the amunt f gypsum in the system. A third system was presented fr testing. This system is a re designed ne frm Cmpany B. It cntains just 5% gypsum, and uses class H cement. Refer t Table 7 results shw this system has a Yung s Mdulus and Pssin s rati much clser t that f Cmpany A. 19

28 Table 7: Mechanical prperties results Service Cmpany A Design B Original B Redesign Yung's Mdulus (psi) Pssin' s Rati 1.24E * *10^5 9.21E E E 01 Ultimate Cmpressive Strength (PSI) 1886 psi psi 1760 psi Tensile Testing Tensile testing was perfrmed using a splitting tensile strength methd. This methd is similar t ASTM C ( standard testt methd fr splitting tensile strength f cylindrical cncrete specimens). Fr this test, the slurry is cured in a 1.5x5 in mld t make three specimens. Afterr curing, each specimen was prepared by cutting ¼ sectin frm each end. Thse pieces were discarded, and the specimen was split int threee 1 inch segments specified as tp, middle r bttm. Density is then calculated fr each segment using Archimedes principle. Each sample is then crushed in the testing apparatus as shwn in Figure 6. The maximumm reading is nted and used t calculate the tensilee strength as per the equatin belw. Tensile strength is calculated by the fllwing equatin: Equatin 1: Tensile strength equatin T(psi) = (2*F) / (Pi*L*D) Where: T = Tensilee Strength (psi) F = Maximum Frce Recrded (lbf) Pi = 3.14 Figure 6: Diagram f tensile test 20

29 L = Sample Length (in.) D = Sample diameter (in.) Tensile test results shw a large difference in tensile strength between the three cement systems tested Tensile Strength (psi) % Gypsum 100% Gypsum 5% Gypsum 20 0 Tensile Testing Chart 5: Tensile strength results 5 Specify Apprpriate Cementing Techniques t Address Issues Identified After reviewing and analyzing the data, sme techniques and changes were discussed. 5.1 Operatins Field data cllected and analyzed thrughut the prject helped identify specific practices that may imprve cement placement peratins. Arund 120 cement jbs were bserved and analyzed. These jbs included surface, intermediate and prductin string. Sme practices fund t greatly impact the integrity f the cement sheath are detailed belw. A checklist f requirements can be fund in the Appendix Paperwrk: Cement jb simulatins and cmplete labratry reprts need t be n hand during all cement jbs. These shw hw the jb is expected t prceed and allws thse n lcatin the ability t make real time decisins abut any issues that arise in the field. Labratry Reprt Pre jb simulatins Lad sheets fr cement and additives Latest maintenance fr equipment Irn certificatins Cement jb prgram based n the simulatin 21

30 Pre jb calculatins: Cement vlumes, displacement vlume, all shuld be calculated independently by the peratr and the cement service cmpany representative prir t the jb. Labratry Testing: A full panel f lab tests shuld be perfrmed n every cement system that is pumped in the Marcellus. These tests are vital t knwing hw cement will perfrm dwnhle. Tests shuld be perfrmed with the same cement, additives and water that will be used in the field. Hwever, if a full suite f tests cannt be run due t timing, at a minimum the fllwing shuld be run and reprted t the drilling engineer and be presented t the representative n lcatin: If the well is vertical: Thickening time Cmpressive Strength (UCA) Fluid Lss If the sectin is hrizntal, in additin t the abve tests: Free water Settling test Every new cement grind and new additive lt shuld be tested fr quality assurance Cement n lcatin: Verify the cement recipe n lcatin matches the recipe in the labratry tests by cmparing the cement lad sheets with the labratry reprt t check that lt numbers match up frm chemical t chemical and the cncentratins are the same n the lad sheet and the labratry reprt. Density and pumping: In all cement systems, density drives the ther prperties. Crrect density will ensure the crrect ratis f cement, water and additives are present fr the cement t perfrm as intended. Density that is lw will have high free water, and pr cmpressive strength develpment. Higher than designed density can lead t shrtened thickening time, higher circulating densities, and higher viscsity. When mixing and pumping cement, density shuld take pririty ver rate. Maintaining a pump rate that allws the cement truck peratr t pump cement at density is recmmended. Typically, this is achieved at rates 4 7 barrels per minute. Jb executin skills: The ability t prperly execute a jb is vital t cement sheath perfrmance. Gd executin skills include: prper pressure testing prcedures, adequate mixing t maintain density, adequate rate, prper cntrl f the cement unit, adequate cement and water delivery t the unit and the ability t trublesht during a cement jb. These skills are typically learned and develped as mre experience is gained. In the jbs bserved, several imprvements had been made in jb executin skills. Timing f casing pressure test: Casing pressure tests are perfrmed t ensure the casing integrity during further well cnstructin r prductin. The casing pressure test is typically dne after cement placement due t ease f peratins. There will already be a plug in place t pressure up against. With a cnventinal cement slurry, this can be dne at the very end f a cement jb, when there is very little chance f the cement building any static gel strength. When the cement is a thixtrpic blend, this is nt recmmended. When the casing is pressured up, it will expand slightly. If the cement has a tendency t develp gel strength 22