Case History: Sequential Re-completions from Toe to Heel in a Horizontal Well Increased Recovery 332%

191/9-26-49-26w3 was drilled in 1996 to evaluate horizontal well with slotted liner recovery relative to perforated vertical well recovery prior to field development.

The slotted liner consisted of three sections of slotted liner or screen with double External Casing Packers bracketing two blank joints to provide isolation for flow testing three slot widths.

There are several lessons from this well’s Case History that validates the principles SCIHOW is based on.

The over-looked lesson is the fact that serial well perforation restored production rate twice and recovery increased more than 2 fold after flow through the slotted liner was uneconomic.

See PETSOC 99-18, “Loading and Sand Cleanout in a Horizontal Heavy Oil Well”. Authors V. Wiebe, D.D. Leung, C.R. Weckesser, R.G. Gillies (available from OnePetro.org)

The conundrum for using horizontal wells in unconsolidated sand reservoirs is that a slotted liner must be installed to prevent borehole collapse but sand exclusion rapidly creates a filtercake that chokes off inflow leaving more than 90% of OOIP in the reservoir.

All things being equal in a reservoir, perforated cold production heavy oil wells recovery is 6 times greater at rates up to 15 times faster than wells that are completed with downhole sand exclusion under the following conditions:

Unconsolidated reservoir sand.
Foamy oil (micro-bubbles in the oil versus solution gas).
Absence of active bottom water.
Ability to effectively extract several hundred cubic meters of near wellbore sand.
Ability to apply maximum drawdown during near wellbore sand extraction.

Oil viscosity, porosity, and permeability are reservoir conditions of minor concern for perforated cold production wells.

Hz wells were relatively new technology when this well was drilled.

Multiple vertical wells had been re-completed to the zone of interest giving a sense of what to expect from the reservoir.

To provide more stringent control on comparing vertical and horizontal well recovery two vertical wells were drilled and depleted then 191/9-29 was drilled off-set and parallel to the two vertical wells.

There were no loss circulation events at this distance from the depleted vertical wells indicating the horizontal well was outside the drained area of the two vertical wells.

The first 150m was in poor quality pay resulting in 700m of trajectory in effective pay.

There were no problems installing or setting the ECP’s or the liner.

Successful installation of the External Casing Packers (ECP) apparently prevented annular flow outside of the liner.

Pack-offs at top & bottom of the scab liner prevented crossflow from the rest of the well.

The PCP was landed above the liner top near the top of the Build Section to minimize rod/tubing failure.

Recovery from 245m of slotted liner exceeded the average of the two off-setting vertical wells by 34% and Initial production rate was 5 times faster.

65% of OOIP was left in the reservoir when inflow through the liner in the Toe was no longer economic.

The scab liner was pulled to evaluate production from the entire liner.

No change in production rate lead to the conclusion there was no inflow through the smaller slot sizes.

An area of good pay was selected for perforating in the Mid-Section.

Rate increased 6 Fold with an IP similar to the Toe section.

There were multiple workovers due to sand inflow into the liner that could not be carried to the pump intake.

Recovery was 70% of the vertical wells.

The immediate up-tick in production rate plus the volume recovered indicates untapped reservoir was accessed when perforating 171m uphole from the economically depleted Toe slots.

Sand was found covering the original perfs in the Mid-Section when preparing to perform the 2nd Perforation Event.

The sand was displaced back through the perforations to the outside of the liner.

Arguably most of the incremental recovery is from the Heel as sand should have re-entered the liner from the Mid-Section perforations.

The lower IP could be caused by 55% of the Heel section in poor quality pay plus rapid re-entry of the sand in the Mid-Section.

Recovery was 29% greater than the off-setting vertical wells.

Oil price affected Economic Depletion rate. Economic depletion occurred at a higher oil rate in 1999 when oil was less than $20 per bbl vs the rate in 2004 for the 3rd Sequence when oil price was above $40 per barrel.

The up-tick in rate plus the volume recovered indicate untapped reservoir was accessed by additional perforating.

This graph illustrates the up-ticks in production rate after each perforating event.

Different declines could be due to reservoir quality or sand influx accumulating in the liner and throttling flow.

This table summarizes the vertical wells’ recovery and rates along with the recovery and rates from each segment of the horizontal well.

Cold production horizontal wells in this area recover about the same volume as a vertical perforated off-setting wells.

Total recovery from this horizontal well was more than triple the average from the off-setting perforated vertical wells.

Each perforation event in the horizontal well accessed untapped reservoir.

The big take-away is that a horizontal well is capable of several times more recovery than vertical wells.

Currently suspended horizontal wells are candidates for re-completions that would restore them to production and ultimately lead to much higher recovery.

Cost Effective removal of the initial high influx of sand is necessary to maximize recovery and profitability.

Since the recovery from each re-completion is similar to a vertical off-setting well’s, and the gamma-ray plus geologist’s strip log identify when the wellbore is in effective pay, the number of re-completions and ultimate recovery can be estimated per horizontal well.

The technique of Sequential Re-completions does not require pre-installed isolation tools on the liner nor does it require plugs in the liner after the re-completion is depleted.

It is designed to perforate, stimulate, and put the well on pump in one run.

Inflow from the perforated interval is contained such that sand & oil inflow is delivered directly into the pump intake.

The pump is landed at the perforations to provide maximum drawdown maximizing sand inflow and oil recovery.

Well servicing and flush-by operations can be carried out by equipment readily available locally.

Besides re-completing currently non-productive horizontal wells, there are about a half dozen more opportunities for using sequenced re-completions to restore productivity and value to cold heavy oil assets.

Sequencing Re-completions in Horizontal Wells provides a step-rate improvement for lower cost cold heavy oil recovery. Contact me so we can get you ready to maximize profits and recovery when the oil price returns.