Isolating horizontal wells without cement

Historically, operators had three choices with regard to long-term wellbore isolation for open-hole horizontal wells: no isolation at all; cementing and perforating; or cement-inflated external casing packers. Cementing and perforating is time-consuming, costly and requires specialized personnel and logistics to handle health, safety and environmental issues. Cement potentially impairs near-wellbore permeability, and a poor cement job allows uncontrolled flow in the annulus, which, in a long, horizontal well, can lead to hot spots, water coning or gas breakthrough. Conversely, having fewer specialized personnel at the wellsite lowers costs and risks to health, safety and the environment. For this reason, many horizontal wells have been completed ‘barefoot’ – that is, without provisions for zonal isolation. However, barefoot completions limit production management and cannot mitigate water or gas production along the wellbore.

New alternatives

New technologies such as swelling elastomers and reactive polymers can provide long-term wellbore isolation in gage-hole wells that previously would have been completed without zonal isolation. These technologies are applicable where barriers are sufficient to prevent migration of fines. In applications where hole geometry is unknown, sand control is necessary, gas is present or an immediate seal is required, an inflatable packer with a core that reacts with wellbore inflation fluid can provide an immediate, long seal for the life of the well without the need for cement inflation.

One such packer is Baker Oil Tools’ MPas. Run as an integral part of the casing or liner string, the MPas uses an elastomeric element with composite structure, which is hydraulically set. Shifting a balance sleeve allows wellbore hydrostatic pressure to act against an atmospheric chamber, which applies setting force to the non-inflatable element for the life of the well. The packer can be set by one of two methods. An inner workstring with setting collet can be used to shift a sleeve in the MPas Packer to activate the setting mechanism as the string is pulled out of the hole. Or, differential pressure can be applied that will activate and set the packer. A lock mechanism maintains the setting force even if hydrostatic pressure is removed, whilst additional setting force can be applied at any time by increasing the hydrostatic or applied pressure at the packer. One-trip deployment and instant sealing allow for immediate testing following activation. The seal element is effective in both water-based and oil-based fluids.

MPas packers can be run on blank casing to isolate unwanted zones, in slotted casing or standalone screens to separate producing zones, or between screens in a gravel pack for zone isolation. The packers have performed impressively on more than 1000 runs in many applications. They have isolated gas caps in wells where the exact positions of the top and base of the gas zone were unknown. They have isolated lost circulation and water in high-angle wells that would be difficult to plug back with cement. And they have been used in many uniform flow wells to enhance the positive effects of uniform inflow control systems by creating a seal between reservoir sections of varying permeability.

Uniform reservoir flow systems such as Baker’s Equalizer system create uniform flow profiles along lateral well sections to optimize reservoir production with fewer wells and significantly reduce field development costs. They also delay water and gas coning and increase the percent of oil recovered. In these systems, MPas one-trip mechanical isolation packers enhance the positive effects of inflow control by creating an annular seal between sections of varying permeability. The combination, spacing and geometry of packers and inflow control devices is determined in advance through detailed engineering analysis. Uniform reservoir flow has been used successfully in sandstone formations and naturally fractured carbonates in horizontal and highly deviated wells with lateral lengths from 400-13,000ft. Benefits realized from uniform inflow control completions range from substantial reduction in gas cusping, water coning and cementing/perforating-related costs to prolonged well life, improved depletion, maximized sweep, effective sand control and reduced need for future well intervention.

Notable successes in Saudi Arabia and Timor Sea

In Saudi Arabia, using an MPas packer in a long, horizontal well across the reservoir sand in the Zuluf field enabled the toe of the lateral to contribute 43 percent of the well’s total production, versus 10 percent from a conventional open-hole completion. Elsewhere, slim-hole (3.5-inch) MPas packers have been successfully run and set with slim inflow control devices (ICDs) through an expandable liner. Other applications in the country include scab liners to consolidate fractures; gas cap isolation to eliminate gas coning; carbonate uniform flow completions, including a 5000-ft horizontal section and dogleg severity of 30 degrees/100ft; uniform flow completions in sandstone; shoe applications; and plug and abandonment with up to 58 degrees/100ft dogleg severity, including one job where circulation was re-gained from total losses at the toe of the horizontal section.

In the Timor Sea, a gas recycling project well team used one-trip MPas packers with slotted liners in a long horizontal section to reduce rig time by eight days, increase production and injection rates to more than 350 MMscf/d and shut off water with no perforation damage or debris.

Water management offshore India

In India’s Mumbai field, where water production rates pose a significant challenge, running an MPas system in open hole below the water zone significantly reduced water content from the previous 93 percent, saved several days’ rig time and eliminated the need to perform a complicated and difficult cementing and perforating operation in a highly deviated well.

In another well, using one-trip MPas isolation packers in a rigless intervention helped lower water production from 2088bwpd to 954bwpd while increasing oil production from 340bopd to 390bopd. The well team also installed sliding sleeves to segment the horizontal open hole into three sections (heel, middle, toe) to study the behavior of the different heterogenic sections and shut off the undesirable portion to reduce water production.

About the authors

Ed Wood is Wellbore Isolation Product Line Manager at Baker Oil Tools, and can be contacted at Edward.Wood@bakerhughes.com. Brent Emerson is Wellbore Construction Product Line Director at Baker Oil Tools and can be reached at Alan.Emerson@bakerhughes.com. For more information, please visit: www.multilateralwells.com.