3,800 3,900
3,500 3,600 3,700
3,400 3,300
3,200 3,100
03:05:11 03:08:31 Bottomhole temperature
Annular bottomhole pressure 03:11:51
Time, h
> Detonation indicators. A coded sequence of pressure pulses is sent downhole to command a perforating gun to fire. Real-time data confirm hydrostatic pressures, firing-head-activation pulses and the perforation event. In this case, downhole pressure and temperature increased substantially after firing.
2,200 psi [15.2 MPa], thus signaling that 1,000-psi underbalance had been reached in accordance with the perforating design. The CCL tool on the ACTive BHA helped to precisely position the guns at the zone to be
90 4 80 3 WI 70 1 60 WI WI 50 Fracture density from FMI log 5 10 2 15 20
perforated. During descent, the CCL detected short pup joints installed above the perforation zone. During the first run, a 10-m [33-ft] gun string was used to perforate a pay interval. With the guns on depth, nitrogen pulses were sent
25
CT bottomhole pressure
Pressure pulse sequence
Guns fired
300 310
280 290
270
260 250
240 230
03:15:11 03:18:31
downhole via the annulus to the eFire-CT electronic firing head system. Upon receiving the correct sequence of pulses, the eFire-CT system detonated the guns. In the control cabin, the operator saw positive confirmation that the guns had fired as programmed: The ACTive sensor recorded an instantaneous increase in bottomhole pressure to 3,700 psi [25.5 MPa], accompanied by an increase in bottomhole temperature (left).
The coiled tubing was then retrieved to surface and the well was flowed to production. Following the perforation of a second, adjacent zone, production was established at 70 MMcf/d [1.98 million m3/d].
Openhole Stimulation in Canada
An operator in western Canada faced multiple challenges while planning matrix stimulation of a multilateral well in a mature gas field. This multilateral well consisted of openhole completions in two branches drilled in a naturally fractured dolomite formation. Along with methane, it produced 21% H2S and 5% CO2. Successful stimulation would hinge on three important factors: • ability of the conveyance tools to enter each branch of the well
• proper functioning of the tools in a subhydro- static environment
• effectiveness of the stimulation fluid in treat- ing the formation.
The subhydrostatic condition resulting from depletion of this mature reservoir limited its ability to support a full column of fluid, which is normally required when using downhole tools that depend on pressure-pulse telemetry.6
The 40 3,200 3,400 3,600 Depth, m
> DTS temperature response to water injection followed by acid treatment. A fracture density plot from an FMI fullbore formation microimager (bottom) indicates the presence of numerous fractures throughout this openhole completion. Following a preacidizing water wash of the wellbore, a DTS survey (blue curve) was obtained. The temperature data show three cold spots (WI) where water has entered formation fractures, noticeably lowering temperatures below the established gradient. The operator expected that these zones would be receptive to the subsequent acid treatment. Another DTS survey (red curve) obtained after the acid treatment revealed four hot spots where fractures were opened by the acid. Zones 2 and 4 correspond to the operator’s expectations, but Zones 1 and 3 proved to be bonuses, where fractures took up acid but had not taken water during the prewash.
3,800 4,000 4,200 0
ACTive matrix stimulation service—with its fiber-optic telemetry, CCL depth control, precise fluid-conveyance capabilities and downhole temperature and pressure measurements—was an ideal alternative. To guide its entry into the intended branch of the well, a multilateral reentry tool was attached to the crossover sub beneath the ACTive BHA. The Discovery MLT multilateral tool consists of an orienting tool and a controllable bent sub. From the surface, the CT engineer can orient the tool azimuthally while controlling the angle of the bent sub to identify the window to each lateral in a multilateral well. Downhole pressure readings allow the engineer to confirm successful entry into the selected leg. After the lateral branch designated for stimulation was entered, depth correlation using the CCL aided in positioning the BHA for optimal stimulation.
32
Oilfield Review
Pressure, psi
Fracture density, fractures/meter
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