This message has been cross posted to the following Discussions: Research and Development and Production .
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While prospecting in the Lloydminster Heavy Oil Belt it became apparent that CHOPS wells and cold heavy oil horizontal wells had similar initial rates and recovered about the same volume of oil. 3-D seismic work done by Pan-Canadian in the 1990's showed an affected area around CHOPS wells that closely matched the calculated area affected by fluid & sand volume produced. The diameter of this affected area is one to two orders of magnitude greater than the width of affected area calculated along the horizontal well lateral positioned in effective pay. Increasing the width of the affected area along the lateral to match the diameter of the affected area of the off-setting CHOPS wells would increase horizontal well recovery.
Serendipity had given me the opportunity to work for a company who had installed sand screens and slotted liners in cold production vertical wells to control sand inflow before the advent of the PC Pump. Sand inflow was prevented, but eventually all inflow ceased. Back flushing with various fluids resulted in a return to sand free inflow, but back flushing had to be repeated several times with the frequency between back flushes increasing to the point where it was no longer economic to continue. In the cases where the sand screen/slotted liner could not be pulled to restore inflow, they were perforated. In either situation sand production was troublesome for a while but it eventually became manageable for the pumps available at the time.
An SPE sponsored course on Rock Mechanics contained a section on sand control methods which lead me to the Risnes and Bratli (1981) experiment that demonstrated that flow rate through an unconsolidated sand pack was the determining factor for managing the rate of sand production for a given diameter perforation. The rate through CHOPS perfs is an order of magnitude greater than the rate through the slots of a slotted liner. Clean out of horizontal well slotted liners generate an insignificant amount of sand relative to the volume of sand produced by CHOPS perf'd wells supporting the Risnes and Bratli experiment.
Another incidence of serendipity gave me the opportunity to be working for a company that was the only case I could find in the Lloydminster Heavy Oil Belt where a slotted liner in a cold horizontal well was perforated. The liner was perforated two separate times, each time restoring economic inflow for a period of time. Cumulative production from the horizontal well was triple that of the vertical offsets as a result of the perf jobs. This is the only cold heavy oil horizontal well I found in this area whose production more than marginally exceeded the off-setting vertical wells.
These perf jobs were not CHOPS. The initial rates after each perf job was in the range of that of flow through slots and little sand was produced. The PC pump was landed at the top of the build section to avoid premature rod & tubing failure resulting in only an 80% draw down, but the largest contributing factor to not achieving CHOPS was the length of each perf interval. The first interval was 50m of 13 shots per meter (spm) alternating Big Hole (BH) and Deep Penetrating (DP) charges. The second interval was 100m of 13spm alternating BH and DP charges. Because there were so many perfs over a large area there was no opportunity to develop the rate required at a given perf to induce CHOPS.
The conclusion drawn from all this is that after production from a horizontal well with slotted liner has become uneconomic, a limited number of BH and DP perforations over a very short interval, with a pump intake landed at the perforations, will result in CHOPS production from that area of the lateral. As with vertical CHOPS wells, inflow will eventually cease. Moving up hole to perforate and land the pump would result in CHOPS production again. With a mile long lateral in a reservoir where the vertical wells drain 2 acres, this process could be repeated up to 16 times for a total capital cost of Cdn $4 to Cdn $6 per recovered barrel. To ensure that OPEX is competitive with vertical CHOPS wells, a jet pump would be required as I could find no viable means of driving a PC Pump in 5 1/2" or smaller diameter liner once the pump was below the build section.
I am looking to work with a company whose assets would benefit from proving this method in reservoirs 1.5m to 6m thick. Currently I would not recommend this method for reservoirs with active bottom water, or, a reservoir with less than 6m of very competent material as a barrier to a lower water zone. Neither would I recommend this method for pay greater than 6m thick as the method will make the reservoir material too weak to support infill drilling of horizontal wells needed for secondary recovery.
I can be contacted directly at 403 357-9032 or
dcadrin@telusplanet.net The attached PowerPoint file expands on what is covered in this posting. There is also a demonstration of how drilling parallel mile long laterals and using sequential limited entry perforating in known fields, even if they have been waterflooded, can result in incremental recovery of 30% at a capital cost of Cdn $7 to Cdn $13.50 per recovered barrel.
Thank you.
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David Cadrin
Director/Consultant/Prospector
D. Cadrin Enterprises LTD
Red DeerAB
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