Cycle time is reduced by eliminating wireline services and combining perforating and fracturing functions in a single operation sequentially treating multiple zones.

Perhaps one of the most versatile treatment techniques is elegant in its simplicity. For some time, the industry has needed a hydraulic fracture treatment that can be applied in almost any well: vertical or horizontal, open hole or cased hole, single-stage or multistage. In spite of current high commodity prices, a challenge facing operators is controlling cost when attempting to improve production in existing wells. Not only must they invest in treatments to stimulate their reservoirs, mitigate formation damage and scale buildup, or attempt to suppress water influx, they must also defer production while intervening to improve it. This double-hit on cash flow can be problematic.

Accordingly, engineers have been looking for ways to reduce intervention costs while at the same time minimize the length of time production must be deferred. Several solutions offer advantages by combining services to reduce the number of trips into the wells to complete the necessary services. Another option is to use coiled tubing (CT) technology. This offers advantages in fast mobilization, rapid rig-up and minimal trip time. Most wells do not have to be shut-in during the intervention and the versatile CT units offer a variety of combinable downhole services so some trips can be eliminated.

The Schlumberger AbrasiFRAC abrasive perforating and fracturing service is an example of the successful combination of downhole services to save time and reduce costs.

Versatility

EOG Resources (EOG) operates in the Sligo field in North Louisiana. The operator produces natural gas from multiple interbedded sandstones of the Hosston formation. Unfortunately, the thin pay sands are interspersed with water-bearing sands. The field is mature and many of its sands are depleted, making them candidates to act as potential thief zones. EOG was looking for an economical way to treat the thin pay zones without stimulating the water zones. Conventional methods previously involved multistage stimulation treatments using traditional hydraulic fracturing techniques. Bridge plugs were used for zonal isolation. While effective, the old method was both costly and time-consuming. EOG needed a fast, effective way to treat the individual zones without jeopardizing depth accuracy, because missing one of the thin zones could nullify any advantages gained.

Using CO2-energized fracturing fluid, the operator treated its wells, which ranged from four to nine individual pay sands. The CT-conveyed abrasive perforating and fracturing service enabled more accurate placement of the individual fractures in the target sands. Moreover, by controlling fracture propagation using variations in pump pressure and treatment volumes, fracture growth into nearby water-bearing sands or depleted zones was avoided. Treatment was performed in one continuous CT operation with a major reduction in completion cost and time-on-location. Most importantly, water production in one case was reduced 85% while gas production was boosted from 1.2 MMcf/d to almost 3 MMcf/d.

Options

Because of its inherent simplicity, combining additional features with the jet stimulation treatment is straightforward. Deployed using CT, the technique enables accurate placement of fracture treatments down the casing or the CT-casing annulus. With its unique jetting action, it requires much lower hydraulic pressure to initiate the fracture than conventional hydraulic treatments. As its name implies, the technique involves directing a high-velocity jet of slurry containing abrasive solids against the target zone, which may be cased or open hole. Accurate depth control is assured using conventional tie-in techniques so even thinly laminated pay zones can be treated. Within seconds, the jet’s highly erosive slurry cuts its way through casing, including liners, pre-drilled or slotted liners, and/or tubing as well as the cement sheath to pierce the formation, thereby initiating the fracture. The abrasive material used is typically 20/40 or 100 mesh fracturing sand. Once the fracture is initiated it propagates conventionally, driven by moderate differential pressure above the natural fracture pressure of the formation being treated (Figure 1).

For multistage operations, sand plugs or bridge plugs can be set to isolate the target formations during treatment. Alternatively, the jet guns can be designed to run with a retrievable bridge plug. The guns are available in various sizes and phasing. Among other available options are fiber-optic downhole tools that provide real-time depth, bottomhole pressure, and bottomhole temperature measurements, telemetered to surface via rugged fiber optic cables. The tools enable distributed temperature measurements that monitor fracture fluid migration as well as the flow profile of the target interval before and after treatment. These options enable completion engineers to evaluate the result of the treatment in near-real time, allowing them to make operational decisions to stop pumping or continue pumping to optimize reservoir contact. The equipment contains a reverse check valve that allows sand to be removed from the well bore by reverse-circulation between stages.

Beside the cost-savings from eliminating explosive jet perforating from the job sequence, its inherent crushed-zone formation damage around the perforation tunnels is suppressed as well. The erosive slurry cuts into the formation without creating a damaged zone. Sand residue can be flushed out after the treatment and any remaining sand will fall harmlessly into the rat hole, no barrier to production.

EOG lowered its completion costs and reduced water production using the AbrasiFRAC technology. The technology is part of the contact family of staged fracturing and completion services designed to maximize reservoir contact. Delivered in four categories, the services are designed to offer a wide variety of solutions depending on the well, the reservoir and the best treatment techniques.

It’s fast too

This technology also was applied by another operator, in South Texas’ Vicksburg field, where traditional techniques for multistage fracturing operations required repeatedly perforating, setting plugs and stimulating for each stage of the operation. In this case, where depth accuracy is not so critical as in the thin pay sands of the Hosston Formation, efficiency can challenge conventional time constraints. The operator switched to the AbrasiFRAC technique and, using its characteristic continuous operation sequences, cut 15 days off the total job time. Not only was job time cut by more than 80%, but gas production from the treated wells more than doubled compared to offset wells in the field completed conventionally.