KoalaWold153‐97‐1‐5‐29‐2HRefracProject
November 22, 2017 Report to the North Dakota Oil and Gas Research Council
SEAN VETTER, JASON BARRETT & CHARLES OHLSONWHITING PETROLEUM CORPORATION
1700 S BROADWAY DENVER CO
NOVEMBER 22, 2017
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ContentsProject Overview ......................................................................................................................................... 2
Summary: ........................................................................................................................................................ 2
Cost Tracking .................................................................................................................................................. 2
Well Selection ............................................................................................................................................... 2
Initial Stimulation ........................................................................................................................................... 3
Offset Frac Impact: ......................................................................................................................................... 3
Preparation for Refrac .............................................................................................................................. 4
Pull Production Equipment and Install Scab Liner .......................................................................................... 5
Clean‐out of Lateral ........................................................................................................................................ 5
Jet Cut Perforating .......................................................................................................................................... 5
The Re‐Frac .................................................................................................................................................... 6
Refrac Pre‐charge ........................................................................................................................................... 6
Pumping the Refrac ........................................................................................................................................ 7
Post‐Frac Cleanout ......................................................................................................................................... 8
Production Results ...................................................................................... Error! Bookmark not defined.
Production Comparison .................................................................................................................................. 9
Return Well to Rod Lift ................................................................................................................................... 9
Initial Learnings .......................................................................................................................................... 10
Next Steps .................................................................................................................................................... 10
Appendix ....................................................................................................................................................... 10
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ProjectOverviewSummary:The Koala Wold 153‐97‐1‐5‐29‐2H (KW 5‐29‐2H) was selected as a top refrac candidate in the Whiting Oil & Gas Corporation (WOGC) Refrac Project (refer to Appendix ‐1, for pre‐refrac Wellbore Diagram). The well preparation, stimulation and post‐stimulation clean‐out were conducted between November 26th, 2017 and June 26th, 2017. The total project was estimated to cost $1.5MM, and actual costs the end of the project were $1.54MM. Table 1 below provides a detailed timeline of events, along with the costs for each phase:
CostTracking
MM/DD/YY 11/26/16-12/7/16 12/7/16-12/20/16 5/29/17-5/31/17
Cost tracking $0-$182k $182k-$462k $462k - $599k
Phase Prepare vertical portion of well bore for Refrac
Cleanout of Lateral and Jet Cut new perfs
Pre-frac formation pressure charge
Detail of Work Performed
Pull rod lift production out of hole, polish the Polish Bore Receptacle, install 5", 18#, P-110 casing from LT to surface as permeant casing and frac string
Cleaned out lateral with 3.75" mill to total depth of 20,356'. No circulation, limited debris after 18,000'. Trip in hole Jet cutting tool and jet cut 56 new perfs.
Pump initial charge at 9bpm @ 3800 psi, after pressure climbed over 4,000, reduced rate to 6.8bpm holding pressure at 3500psi. Pumped total of 10,348bbls.
MM/DD/YY 6/1/17-6/5/17 6/9/17-6/17/17 6/17-Present
Cost tracking $599k-$1,283MM $1.283k-$1,455k $1.45MM-$1.54MM
Phase Refracture Stimulation Clean out of Lateral Post Refrac
Run production tubing and Flowback
Detail of Work Performed
1-4 cycles - 195k # 100 mesh, 5k bbls at 55bpm, 6300 psi cycle 5-17, same targeted rate but including physical diverters (balls) and chemical diverters.
Clean out to bottom with retrievial of heavy sand and ball diverter. Maintained circulation w/ 2bpm rate and pressures at 500-900 psi.
Following cleanout, 2/78ths by 2 3/8ths taperd tubing string run into a packer set at 10,371'. Took off flowing after a 2 swab runs and has flowed from 6/22 until the time of this report (19 days).
Table 1. Detailed Chronology and Costs for KW 5‐29‐2H Refracture Operations
WellSelectionTo ensure the greatest likelihood of success in creating an economic project, choosing the correct well for re‐stimulation was the most important step. The selection process posed the following questions:
1. Were the initial stimulation design and execution adequate, compared to current standards? 2. Was the job pumped as designed, or were there any equipment failures or execution failures that
resulted in a disappointing initial completion? 3. Is the well performing to expectations and successful offset wells, or is it underperforming for
reasons that could be attributed to completion method or a loss of connection between the well and the formation?
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InitialStimulationDetails
Completed March 2013 (by KOG)
Plug and Perf (1‐ 6’ cluster/stage)
Cemented 4.5” Liner
21 stages (isolation plugs)
72,000 bbls water/slurry
Cross‐linked 35# borate gel
3.5MM lbs 20/40 Ceramic prop
Post Frac Cleanout only reached plug #18 (18,218’)
The original completion outlined above was reasonably common at the time, except for ceramic proppants, which was considered a premium completion component at the time. Compared to current practices though, the original KW 5‐29‐2H completion was lacking in many areas: the total stage count and stage spacing were too modest to adequately stimulate and drain the reservoir along the lateral, the proppant loading was very low, and the water volume and fluid system methodology (high gel‐load cross‐link vs slick water or hybrid) did not provide the stimulated reservoir volume necessary to adequately drain the reservoir along the lateral. In addition to the ceramic proppant, another upgrade that the KW 5‐29‐2H offered was a cemented liner, affording a refrac opportunity with a higher confidence in annular isolation than open‐annulus/packer completions that were more common at the time.
CumulativeProductionIn addition to the undersized initial completion, the KW 5‐29‐2H had been underperforming compared to similarly completed Bakken offset wells (Figure 1), further lending to the high likelihood of a successful refrac candidate.
Figure 1. Offset Cumulative production and Relative location
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OffsetFracImpact: An important screening metric when evaluating refrac candidates is the observed impact to production on existing, offset “parent wells” when new infill “child wells” are drilled and completed nearby. In particular, if a frac on the child well results in a positive production “bump” in the parent well, positive refrac results in the area are expected to be more likely. As shown in Figures 2‐4, such a scenario was recently observed near the KW 5‐29‐2H. In the DSU’s directly south of the KW 5‐29‐2H, a new infill well was drilled and completed next to an existing parent well, and upon completion, the parent well experienced a significant and sustained production increase.
Figure 2. (top) Map of offset frac strike well
Figure 3. (bottom left) Daily production of parent well that was frack struck Figure 4. (bottom right) Cumulative Oil Production indicating slope change from frac strike
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PreparationforRefracPullProductionEquipmentandInstallScabLinerThe KW 5‐29‐2H was first prepared by pulling the rod pump equipment and tubing out of hole. During a previous workover for a downhole equipment failure in August 2016, a caliper log had been run, showing two (2) partial collapses of the 7”, 32 lb/ft, HCL‐80 grade casing at 7,222’ and 8,566’. Coincidently, these depths corresponded with the Oppeche Salt and Charles Salt formations, occasionally associated with casing collapses in certain parts of the Williston Basin. To prevent further salt encroachment, ensure wellbore stability and allow for the necessary production equipment, a permanent 5”, 18 lb/ft, P‐110 grade casing string was run from the liner top to surface and cemented in place. Cumulative costs to date were $182,000.
Clean‐outofLateralTo ensure the KW 5‐29‐2H’s lateral was entirely open and fully prepared for the refrac, it was necessary to clean‐out the wellbore to the total original depth of the well (TD). The original attempt to drill‐out frac plugs after the primary completion only reached a depth of 18,218’, leaving three (3) frac plugs un‐drilled. The lateral cleanout was accomplished in three (3) days, and the three (3) plugs previously left in the hole were successfully drilled‐out. During the clean‐out, the workover rig was unable to achieve full circulation, indicating the open perforations were connected to partially‐depleted reservoir.
JetCutPerforatingAs previously mentioned, the KW 5‐29‐2H was completed in 21 stages, with only 1 perf cluster per stage. This completion design left approximately 750’ of uncompleted lateral and un‐contacted reservoir between each perf cluster, resulting in a substantial opportunity for refrac. In previous refrac projects WOGC perforated additional holes in the casing between existing perforations using standard shaped‐charge perforation explosives run on tubing‐conveyed guns. For this project, WOGC opted to perforate the casing between existing perf clusters (to create additional entry points into formation) using an abrasive jet‐cutting tool (Table 2). This process involved running a jet‐cutting tool on tubing and pumping water and sand through the tool to abrasively erode holes in the casing (Figure 5). WOGC recognized that the resulting jet‐cut perforations would more easily allow the planned refrac to stimulate new portions of the reservoir than standard explosive‐charge perforations would have allowed.
Figure 1. Model of Jet‐Cut Spacing
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Table 2. Abrasive Jet Cut Perforations (NEW) vs Existing Perforations
After the jet‐cutting operation, WOGC experienced logistical issues with frac resources, and found that modifications to the newly installed 5” scab liner would be necessary. Due to these events, the planned refrac was delayed until it could be rescheduled in May 2017. Since the modification work to the 5” scab liner was necessary to ensure the ongoing integrity of the wellbore irrespective of the refrac, those costs were deducted from the refrac project total resulting in a cumulative cost to date of $462,000.
TheRe‐FracRefracPre‐chargeThe primary goal of the planned refrac was to develop new reserves by accessing and stimulating new portions of the reservoir in areas the initial completion failed to stimulate. The initial step to successfully diverting away from existing, depleted perforations and into new perforations was to inject a high “pre‐charge” volume of treated water into the well. To accomplish this, a total of 10,350 bbl of treated water was pumped at a low rate (6 ‐ 9 bpm), all while remaining under a maximum pressure corresponding with the fracture initiation pressure. Exceeding fracture initiation pressure was believed to reduce the chances of dispersing the pre‐charge fluid to all portions of the lateral. Cumulative costs after the pre‐charge were $599,000.
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PumpingtheRefracThe refrac pumped on the KW 5‐29‐2H comprised a total of 2.365 Million pounds (MMbls) of proppant in 60,160 barrels (bbl) of fluid. The 2.365 MMbls of total proppant included 1.277 MMlb of 100 mesh and 1.088 MMlb of 30/50 Premium White proppant. The fluid system used was a Hybrid fluid system, including three (3) different types of fluid: (1) Slickwater, (2) 20 lb/Mgal Linear Gel, and (3) a 20 lb/Mgal Zirconate Cross‐Linked gel. Proppant was primarily pumped in the Linear Gel and Cross‐Linked Gel portions of the refrac. The refrac was pumped in seventeen (17) cycles, each cycle separated by diversion material. A total of 5,000 lbs of particulate diversion material was used (PolyLactic Acid) along with a ThruTubing Solutions product called SlicFrac PCL™ Perf Pods. Figure 6 below shows the plot of the KW 5‐29‐2H refrac:
Figure 6. Treatment plot for KW 5‐29‐2H refrac, 17‐cylces
The refrac was pumped at an average rate 54.4 barrels per minute (bpm), and an average pressure 6,458 psi. The total volume of clean fluid pumped was 60,160 bbl, and the total slurry volume was 62,475 bbl. The post‐job Instantaneous Shut‐in Pressure (ISIP) was 4,331 psi. Over the course of the refrac, pressures indicated new reservoir was being accessed with much of the refrac, measured through ever increasing ISIP’s. Figure 7 shows the increasing ISIP’s between cycles, corresponding with increasing gradients of minimum horizontal stress throughout the refrac, and gives a positive indication of refrac performance and the successful diversion away from existing perforations.
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Figure 7. Increasing ISIP’s between cycles, corresponding with increasing gradients of minimum horizontal stress
Referencing Figure 7 above, it’s estimated that during stages one (1) through three (3), the initial refrac cycles stimulated the existing fractures from the initial completion. Refracturing the existing fractures benefited the well by overcoming degradation or scaling that may have occurred over the last several years. After reaching the estimated gradient of minimum horizontal stress (0.78 psi/ft in this case), the remaining cycles stimulated new reservoir volume, opening new parts of the reservoir, helping develop new reserves. The refrac started on June 1, 2017 at 11:52 PM and ended on June 4, 2017 at 5:53 AM. All seventeen (17) cycles were pumped as planned, although the aggressive manner of diversion screened‐out the refrac at one point, requiring WOGC to flowback the well prior to resuming the remainder of the refrac. The cumulative cost after the refrac was $1,283,000.
Post‐FracCleanoutThe KW 5‐29‐2H was shut‐in after the refrac, and a composite bridge plug was run and set just below liner top to serve as a “kill plug”. A 24‐hour Workover Rig was used to drill‐out the frac plugs and clean‐out the wellbore. After the drill‐out was complete, a packer and tubing were installed in the well, and it was flowed for clean‐up and put on production. The cumulative cost after the clean‐out was $1,540,000.
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ProductionResultsProductionComparisonPrior to being refrac’d, the KW 5‐29‐2H was being rod‐pumped with a 1‐1/2” insert pump seated at 10,073’. The fluid level indicated that the well was pumped‐off, producing an average 70 BOPD, 134 MCFPD and 119 BWPD. The post‐refrac IP (peak 24‐hour rate) was 639 BOPD, 1238 MCFPD and 1366 BWPD. The first 30‐day average production was 317 BOPD, 1030 MCFPD and 856 BWPD. In mid‐August 2017, the KW 5‐29‐2H was shut‐in for offset frac operations, but re‐opened in September 2017 when the offset operations were finished (Figure 8 below).
Figure 8. Before and After Daily Production
ReturnWelltoRodLiftThe KW 5‐29‐2H continues to flow up tubing and packer. The final step to the refrac will be to install artificial lift once the well loads‐up to the point it can no longer free‐flow. A 2” insert pump with a mechanical capacity of 400 BFPD will be installed. After this work, the final job costs are estimated to be $1.62MM, compared with the $1.5MM originally budgeted. The overspend is attributed to increases in vendor pricing between onset of project and completion due to increases in demand for those services.
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InitialLearningsThe KW 5‐29‐2H was WOGC’s first refrac of a well having an older‐generation completion, but the benefit of a cemented liner. There were some very important lessons learned during the preparation for the refrac, the refrac execution and the post‐refrac work.
The frac string was able to be run and tested successfully, despite the age of the well, ensuring wellbore integrity during the refrac;
The pre‐refrac pre‐charge was adequately designed and helped the refrac divert away from the original fractures early in the refrac;
The perforations made with abrasively‐jet perforating the cemented liner appeared to have aided in helping stimulate new parts of the reservoir between the existing perforations; and
Increasing ISIP’s and corresponding frac gradients indicated a successful diversion away from existing fractures.
NextStepsOver the next several weeks and months, WOGC will be closely monitoring the KW 5‐29‐2H. Recently the well has started exhibiting liquid‐loading, and it is anticipated to be converted to rod‐pump over the next few months. After that, the well will be monitored with production tests, fluid shots, and fluid analyses. WOGC will be striving to optimize the production from the KW 5‐29‐2H by ensuring the artificial lift is appropriately sized, and changed if necessary to capture as much value from the refrac as possible. Based on the early flowback information, the initial production from the refrac will meet and exceed WOGC’s expectations. The next performance metric WOGC will evaluate for the refrac will is the way the production decline and estimation of incremental reserves.
Appendix1. Original Wellbore Diagram, prior to Refrac 2. Resulting Wellbore Diagram, post Refrac
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1. Original Wellbore Diagram, prior to Refrac
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2. Resulting Wellbore Diagram, post Refrac
