CHOPS began when the progressing cavity pump overcame rod float making it possible to achieve maximum drawdown. At maximum drawdown disintegration of the near wellbore matrix and other formation alterations take place that increase rate and recovery.
Insular depleted areas form around a well when draining fluids from unconsolidated sandstone. This leaves up to 90% of the reservoir unaffected by production.
Horizontal wells in unconsolidated sandstone are designed to prevent sand inflow while obtaining production from long continuous sections of reservoir. Preventing sand inflow obstructs ultimate recovery. The long wellbore produces high rates that payout drilling and completion in an acceptable amount of time, but horizontal wells have been economic failures as they cost twice as much to drill and complete as a vertical CHOPS well for similar recovery. Horizontal well CHOPS can change this.
It follows from these observations that Horizontal Well CHOPS would increase recovery in two ways:
- Inducing sand inflow would widen the drained area along a horizontal wellbore up to two orders of magnitude.
- Spacing sequential CHOPS re-completions from the Toe to Heel of the well would be similar to an equivalent number of vertical CHOPS wells placed close enough together that their depletion areas meet or overlap.
Each time the well reached economic depletion perforating the liner generated incremental oil recovery.
The first perforation event was placed in a section of the liner approximately half way between the depleted areas of the off-setting vertical wells. Recovery was 70% of the average from the off-setting vertical wells.
The second perforation event is less informative in terms of the source of inflow due to perforations being made in the heel, mid-liner, and toe. Still, it successfully restored production and recovered 129% of the average from the off-setting vertical wells.
Of the 576 horizontal wells studied in this region, this was the only one found to be perforated after initial economic depletion. Also, it was the only horizontal well that recovered multiples of the volume of off-setting vertical wells.ur own text
Conventional oil horizontal well producers report that re-completion of liners by perforating to allow for controlled intermittent production of solids for brief periods stimulates inflow that had been declining. The paradigm shift from doing all that was possible to prevent sand inflow, to doing all that is possible to maximize sand inflow occurred in cold heavy oil with the introduction of the PCP. These two situations exemplify that when the benefits of inducing sand inflow become apparent, engineered solutions for producing, handling, and disposing of produced sand become part of the daily operations.
Knowing CHOPS has a finite diameter depleted area, re-completions would have to be sequenced from Toe to Heel to tap all of the reservoir along the length of the well.
Effective sand removal at the perforations is critical for CHOPS recovery. Attempts to keep long perforation intervals open would require multiple expensive workovers and production tubing would likely get stuck in the liner. Very short lengths of perforations could be kept virtually sand free using common operating practices.
With no downhole moving parts, effective operation at any angle, ability to pass through the build section without damage, no rod string, no electric cable, relatively small diameter, short length, low risk of destruction when pumped off, and the ability to produce high solid content fluids and viscous fluids are attributes that make the jet pump more suited to this application than other pump systems. Although it has a reputation for lower efficiency and greater energy consumption than other pump systems, it is the pump for this job.
This region has multiple pay zones. Typically a vertical well is not drilled with the Lloydminster being the sole target because the recovery is too low for an attractive capital cost per recovered barrel.
The CAPEX for vertical wells targeting only the Lloydminster provides insight into the relative profitability of exploiting this large asset using vertical wells or horizontal wells. Further, it would require 224 vertical wells to access the same amount of reservoir as the 14 horizontal wells.
Recovery from horizontal well CHOPS depends on how much of the wellbore is in effective pay. Effective pay is determined by reservoir heterogeneity and planar unevenness. A 1,500m wellbore can have 16 re-completion sequences spaced at 100m intervals. If each re-completion sequence produced the average volume of oil derived from the vertical off-setting wells, this is deemed as 100% of the wellbore being in effective pay.
The CAPEX presented for re-completing existing horizontal wells, and for drilling parallel horizontal wells, represents 100% to 50% of the wellbore being in effective pay.
Generally, thicker pay would result in wider well spacing and re-completion spacing. Combined with more oil recovery per meter of wellbore, thicker pay would require less capital per recovered barrel.
Pad drilling is known to reduce drilling costs.
Adding horizontal well CHOPS to pad drilling provides these other capital cost reduction opportunities:
- Pad drilling 14 parallel horizontal wells requires 60% less surface land than 16 wells on 40 acre spacing.
- Wellhead proximity and longer well life promotes infrastructure savings in flowlines, solution gas gathering, central treating facilities, sand disposal, oil sales, SCADA control and monitoring, and electrification.
- Follow up flood schemes would not require infill drilling nor extensive additional flowlines.
1,500m horizontal wells in the previously mentioned Lloydminster zone produced at 7 to 15 times the rates of the off-setting vertical wells. At these rates drilling and initial completion pays out in an acceptable length of time. Follow-up horizontal well CHOPS sequential re-completion production rates will be lower but re-completion costs are an order of magnitude less than drilling a vertical well. This lower cost for 16 re-completions per horizontal well makes less prolific zones attractive long life resource plays.
Successful horizontal well CHOPS should leave a marginal amount of residual oil. If the remaining volume of oil becomes economically attractive, the length of reservoir directly accessed by parallel horizontal wells would improve the effectiveness of secondary recovery schemes.
Thirty-five years ago practically no one could imagine that a progressing cavity pump would be competitive with a pumpjack and rod pump, let alone that it would totally replace them and create a step change in profitability and recovery of cold heavy oil.
Similarly, until today, it would have been challenging to consider that another step change in cold heavy oil recovery and profitability could be achieved by causing sand laden fluid production from horizontal wells.
We know that oil prices cycle. Low oil prices provide auspicious circumstances to begin the process of sequential re-completion of economically depleted horizontal wells such as:
- A dormant paid out capital asset can be re-activated and re-completed for about 60% the cost of drilling a new vertical well to maintain production and cashflow.
- Equipment and services are typically less expensive during times of low oil prices.
- Greater than 50% of the estimated initial re-completion cost is equipment that is expected to serve the 20+ years life of a horizontal CHOPS well.
- Proof of profitable incremental recovery would emerge about the time the oil price cycle is beginning to increase adding value to reserves.