Uncertainty Factors
The initial review of data from other wells in the field, showed how challenging this project would be. As with many mature fields, the Geologist had to contend with data of different vintages and qualities. Another big problem was caused by a paucity of log data across the zone of interest. In this field, the former Operator’s practice was to set casing in the shale immediately above the Whirlpool sandstone, and then TD the well before penetrating the base of the sand. Due to the sensor configuration of the wireline logging tools, most logs obtained from such wells showed only 30 or so feet of open hole, and no trace of the base of pay. In fact, only 2 wells completely drilled through the pay zone.
The Geosteering team identified other issues as well:
- Well logs in the Roberts #3 Original Hole ended above the base of the pay zone, so exact thickness of this formation could not be determined.
- Surface elevations of wells previously mapped were verified by GPS surveys to ensure that no elevation changes were caused in preparing these wellsites. The GPS elevations revealed several wells that needed slight adjustments in ground elevation. These slight adjustments were critical for mapping a zone that was only 8-10 feet thick.
- Lack of good well cutting samples was another concern. The only well in the field that had any samples was the Roberts #3. This well was drilled by a cable tool rig, and sample depths were found to be off by 19 feet from the wireline log measurement.
- An azimuthal LWD tool was recommended, but fell outside the budget constraints for this project. Without the benefit of an oriented resistivity log while drilling, the Geosteering Team would have to rely heavily upon the gamma ray log (which is 34’ behind the bit), drilling rate, cuttings, and hotwire to stay within the target zone.
Project Budget Geosteering
After devising a Geosteering Plan and Wellbore Plan, HSC formulated an AFE to appropriate $541,900.00 for the project. The Drilling Contractor, Mudlogger, Directional Drilling Contractor, Tubulars, Drilling Fluids and all other ancillary services were selected on the basis of lowest bid and local experience.
A general breakdown of costs is provided in the table below:
| General Cost Category | Budgeted Cost |
|---|---|
| Wellhead Equipment | $ 11,550 |
| Pre / Post-Drilling Costs | $ 111,426 |
| Drilling | $ 370,124 |
| Clean-up / Stimulation | $ 41,900 |
| Pipeline Reconnection | $ 6,900 |
| Total AFE | $ 541,900 |
Roberts #3 Sidetrack Operations Sequence
The well was sidetracked and directionally drilled in the following sequence.
Moved in coiled tubing unit to acid wash the formation in preparation for logging well. Ran Circumferential Borehole Imaging Log for fracture orientation. Determined that faults were aligned to the northeast. Set bridge plug at top of pay zone and at KOP.
Moved in drilling rig. Set whipstock at 3092’, oriented at N28W (casing shoe at 3177’). Milled a window in the 5 1/2″ casing from 3074-3093’ (90’ above pay zone). This window was judged to be insufficient for passage of the BHA, so the window had to be re-milled (thus setting the drilling schedule back by 1 1/2 days). Rigged up Mudlogging Unit with gas chromatograph and hotwireo monitor gas fromhe shale shaker, ando describe formation cuttings. Rigged up MWD unit for real-time gamma ray and directional data.
Ran in hole with directional drilling assembly, including 4 3/4 inch bit, mud motor, nonmagnetic flex drill collars and MWD equipment. Directional Driller gyroscopically oriented the motor. Drilled new 4 3/4″ hole at 3093’, sliding with 3º mud motor.
A survey obtained at 3129’ measured only 18º of angle. This survey alerted the Geosteering Team to the distinct probability that a 3º mud motor would not provide a build rate sufficient to land horizontally in the Whirlpool sand.
Tripped out ofhe hole to install a 4º mud motor and bit #2. Drilled new 4 3/4″ oriented hole from 3129’ to 3196’, sliding with motor. (Built angle increased from 18º to 64º.) Directional Drillers projected that the wellbore would land horizontally in the Whirlpool, now expected at 3203’ TVD -at which point the wellbore would be 155’ away from the original hole.
Tripped out of the hole for new bit #3, and changed back to 3° mud motor (set at 2.12°). Drilled 4 3/4″ oriented hole from 3196’ – 3237’, sliding with motor. (Built angle to 75º). Rotated and drilled 4 3/4″ hole from 3237’ – 3255’. Drillers projected that the target is 1 foot below present depth. Background gas increased four-fold, from 2 to 8 units. Continued drilling 4 3/4″ oriented hole from 3255-3281,’ rotating with motor. Entered Top of Whirlpool at 3259′MD/3195′TVD (111.1 Vertical Section), noticed increase in ROP, sand content and gas readings (Angle 76.7º at top of Whirlpool sand).
Tripped for new bit #4. Drilled 4 3/4″ oriented hole from 3281 – 3475’, sliding and rotating with motor. The 3º motor was set at 2.12º (survey angle = 91º). MWD log showed that, upon reaching a depth of 3323’ MD (3203’VD, 173’ VS), wellbore encountered Lower Whirlpool, (a low-porosity zone), 8 feet below top of sand. Basically, the build radius was bottoming out at the very base of the Whirlpool.
Tripped for new bit #5, reset 3º motoro 1.83º. Drilled 4 3/4″ hole from 3475 – 3656’, rotating and sliding with motor. Encountered fracture zone, accompanied by lost circulation, at 3650 – 3656’. Pumped lost circulation material downhole, then drilled ahead to 3749’.
Tripped for new bit #6, maintained motor setting at 1.83º. Drilled 4 3/4″ hole from 3749 – 3865’, rotating and sliding with motor. Drilling ceased upon reaching a sharp decline in bit performance. At this point, the budget was essentially spent.
Final survey at TD: 3865′MD/3190.48′TVD -Angle = 91.3º -Azimuth = 329.1º -North:618.9’ -East:358’
Pre-and Post Performance ofhe Well
After reaching TD, a coiled tubing unit moved in to clean out the well with a nitrogen foam and acid wash. The well attained an initial flow of 5800 MCFD, and average flow of 5000 MCFD, along with substantial amounts of water that had been introduced during lost circulation and during coiled tubing operations. (Previous meter observations on the Roberts #3 Original Hole showed 2300 MCFd maximum and 1750 MCFd average flows during high production periods.) A four-point back-pressure test has been scheduled for the near future.
Budgeted and Actual costs
The goal of extending a horizontal wellbore updip between two faults was attained within 1.5% of the budgeted cost, despite additional milling to open a window in the casing, and encountering lost circulation in the storage zone. A table comparing budgeted and actual costs is shown in the table below:
| Cost Category | Budgeted Cost | Actual Cost | Variance |
|---|---|---|---|
| Wellhead Equipment | $ 11,550 | $ 9,807 | $ 1,743 |
| Pre/Post-Drilling Costs | $ 111,426 | $ 107,191 | $ 4,235 |
| Drilling | $ 370,124 | $ 390,118 | ($ 19,994) |
| Clean-up / Stimulation | $ 41,900 | $ 38,600 | $ 3,300 |
| Pipeline Reconnection | $ 6,900 | $ 4,653 | $ 2,247 |
| Total AFE | $ 541,900 | $ 550,369 | ($ 8,469) |
An analysis of major variances in well cost shows that savings were achieved in some areas, and losses were experienced in others. The over-runs can be loosely grouped into two main groups, consisting of Site Work and Operations. A good portion of the Operations over-runs can be attributed to the cost of additional time required to mill the casing window, along with time and materials devoted to remediation of lost circulation.
| Cost Category | Budgeted Cost | Actual Cost | Variance |
|---|---|---|---|
| Site Preparation | $ 5,000 | $ 14,375 | ($ 9,375) |
| Engineering Survey | $ 7,000 | $ 13,000 | ($ 6,000) |
| Logging | $ 20,000 | $ 13,000 | $ 7,000 |
| Mud Logging | $ 3,750 | $ 9,247 | ($ 5,497) |
| Setting Plugs | $ 15,000 | $ 11,000 | $ 4,000 |
| Disposal | $ 15,000 | $ 7,500 | $ 7,500 |
| Drill Bits | $ 45,000 | $ 43,000 | $ 2,000 |
| Whipstock | $ 32,000 | $ 30,000 | $ 2,000 |
| Mobilization | $ 40,000 | $ 48,000 | ($ 8,000) |
| Fuel | $ 8,000 | $ 5,400 | $ 2,600 |
| Drilling | $ 129,000 | $ 152,197 | ($ 23,197) |
| Contingencies / Miscellaneous Equipment | $ 72,000 | $ 53,500 | $ 18,500 |
| Total Cost Over-Run | ($ 8,469) |
Conclusion
This well marked the first horizontal well drilled in the Honeoye Storage Field, and provided 606 feet of exposure to the Whirlpool Sandstone. This exposure fell within the limits established by the Geosteering Plan.
The experience gained from this well will serve as a guide for planning and drilling additional horizontal wells in the Honeoye Storage Field. Based on this well, it has been determined that any future horizontal wells drilled at Honeoye will be drilled from new locations, rather than milling out and sidetracking from an existing well. Given the cost of milling out, and the restriction in hole size, it was deemed more beneficial to drill an original hole, which would provide a larger hole size, thereby increasing reservoir exposure, while avoiding the cost spent in milling through casing.
