4,000 4,500
1,000 1,500 2,000 2,500 3,000 3,500
500 0
0 500 Vertical
perforations 1,000
Openhole completion
Horizontal perforations
1,500
2,000
2,500 Reservoir pressure, psi
> Critical drawdown pressures for three scenarios of perforated completions in a Mirren horizontal well. The rst scenario considered an openhole completion (red). The second scenario examined drawdown conditions when perforations are shot horizontally (green), and the third case shows the drawdown conditions when vertical perforations are used (blue). The vertical perforations clearly produce the largest sand-free window and suggest the reservoir sand should not fail until the reservoir pressure declines to less than 500 psi [3.4 MPa].
3,000
3,500
4,000
4,500
This 3D model, originally developed to provide wellbore-stability information, enabled the suc- cessful drilling of two wells in the field.27 Significantly, the 3D model predicts that the maximum stress orientation near the diapir is tilted 20° to 40° from horizontal, potentially impacting BP sand-avoidance efforts in two planned horizontal production wells, the East and West wells. Building on the MEM, BP con- structed a geomechanical model along the planned trajectories of two of the wells using log data— including gamma ray, compressional traveltime, tc, and density data— core measure- ments, leakoff tests and reservoir pressure measurements from offset wells. Shear data, or ts, were estimated using compressional informa- tion from the sonic tool. The dynamic rock properties calculated from the sonic and density measurements were converted to static proper- ties and then calibrated to rock strengths measured in cores from offset wells. In addition, BP analyzed the average grain size in cores of the Mirren fi eld reservoir rock.
Openhole
Perforation Inclination 10
deg 0
Compressive Strength kPa
1.95
Bulk Density gm/cm3
Unconfined 60,000 2.95 3,300
Critical Drawdown at 2,000-psi Depletion
-1,000
Critical Drawdown psi
5,000
Sandstone Shale
-1,000
Critical Drawdown at 3,000-psi Depletion
Critical Drawdown psi
5,000 -1,000
Critical Drawdown at 3,000-psi Depletion
Critical Drawdown psi
5,000 Vertical -90 Sandface Failure
Critical Drawdown at Initial Reservoir Pressure
Horiz ontal Perforation Sandface Failure
Critical Drawdown at Initial Reservoir Pressure
Vertical Perforation Sandface Failure
Critical Drawdown at Initial Reservoir Pressure
3,400
3,500
> Continuous critical drawdown data. Track 1 displays vertical perforation orientation, computed uncon ned compressive strength (UCS) and bulk density data. The three scenarios are presented in Tracks 2, 4 and 5. The openhole case is run using a depletion of 2,000 psi [13.8 MPa], while the perforated scenarios use a depletion of 3,000 psi [20.7 MPa]. The light green area represents the critical drawdown at depletion, and the critical drawdown at the initial reservoir pressure (dark green) is also presented.
20
Oilfi eld Review
Critical bottomhole flowing pressure, psi
Depth, m
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