Updating the Geomechanical Model and Calibrating Pore Pressure From 3D Seismic Using Data from the Gnu-1 Well, Dampier Sub-basin, Australia
- Adrian White (Geo Mechanics International) | Brett McIntyre (Apache Energy) | David Castillo (GeoMechanics International) | Julie Trotta (GeoMechanics International) | Marian Magee (GeoMechanics International) | Christopher D. Ward (GeoMechanics International) | Paul O'Shea (Apache Energy)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2009
- Document Type
- Journal Paper
- 408 - 418
- 2009. Society of Petroleum Engineers
- 3 in the last 30 days
- 846 since 2007
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A post-mortem analysis of the Gnu-1 well was conducted to help us to understand drilling experiences in the context of the pore-pressure and stress profiles. The post-mortem involved a review of the drilling experiences and an analysis of CAST image data, wireline-log data, and the logging-while-drilling (LWD) logs. This information was used to refine and verify a geomechanical model (in-situ stress, pore pressure, and rock-mechanical properties) in the vicinity of the Gnu-1 well. Of prime concern was the verification of the predrill pore-pressure prediction previously undertaken using 3D-seismic-velocity data and offset-well data. Wellbore-failure and natural-fracture analyses were integral parts of the post-mortem. Wellbore breakouts seen in the image data allowed the pore pressure in the 8.5-in. hole section of Well Gnu-1 to be constrained. Modeling using image data collected in the Athol formation indicates that the pore pressure does not increase as rapidly as was estimated in the predrill study. Pore pressures in the North Rankin formation and below were consistent with the predrill study. The geomechanical model was able to explain the losses seen in the Athol formation in Well Gnu-1 when using the mud weights experienced by the open hole at the time of drilling.
The Gnu prospect is situated in the northern portion of Block WA-209-P in the Dampier subbasin, Australian northwest shelf (Fig. 1). The prospect is located within the Reindeer gas field. A number of offset wells exist in the region, the closest wells being Well Reindeer-1 (approximately 1.5 km to the northeast) and Well Caribou-1 (2 km to the southeast).
Well Gnu-1 was designed as an exploration well. The anticipated overburden stratigraphy at the location of Well Gnu-1 consists of Tertiary and Upper Cretaceous carbonates, marls and siltstones that overlie Cretaceous claystones, siltstones and minor sandstones, and greensands. The primary aim was to drill vertically to intersect the Muderongia australis glauconitic sandstone and then to build angle and continue drilling a deviated hole through the main Reindeer field gas appraisal within the Legendre formation and into the North Rankin, Brigadier, and Mungaroo formations.
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Aadnøy, B. and Bell, J.S. 1998. Classification of drilling-induced fracturesand their relationship to in-situ stress direction. The Log Analyst39: 27-42.
Barton, C.A., Zoback, M.D., and Moos, D. 1995. Fluid flow along potentially active faults in crystalline rock.Geology 23 (8): 683-686.doi:10.1130/0091-7613(1995)023<0683:FFAPAF>2.3.CO;2.
Bell, J.S. 1990. Investigating stressregimes in sedimentary basins using information from oil industry wireline logsand drilling records. Geological Society, London, SpecialPublications 48: 305-325. doi:10.1144/GSL.SP.1990.048.01.26.
Ewy, R.T. 1999. Wellbore-Stability Predictions by Useof a Modified Lade Criterion. SPE Drill & Compl 14(2): 85-91. SPE-56862-PA. doi: 10.2118/56862-PA.
Hermanrud, C., Wensaas, L., Teige, G.M.G., Nordgård-Bolås, H.M., Hansen, S.,and Vik, E. 1998. Shale porosities from well logs on Haltenbanken (offshoremid-Norway) show no influence of overpressuring. In Abnormal Pressures inHydrocarbon Environments, ed B.E. Law, G.F. Ulmishek, and V.I. Slavin,65-68. Tulsa: AAPG Memoir 70, AAPG Publications.
Hillis, R.R. and Williams, A.F. 1993. The contemporary stress field of theBarrow-Dampier Sub-Basin and its implications for horizontal drilling.Exploration Geophysics 24 (4): 567-576.doi:10.1071/EG993567.
Horsrud, P. 2001. EstimatingMechanical Properties of Shale From Empirical Correlations. SPE Drill& Compl 16 (2): 68-73. SPE-56017-PA. doi:10.2118/56017-PA.
McNally, G.H. 1987. Estimation of coalmeasures rock strength using sonic and neutron logs. Geoexploration24 (4-5): 381-395. doi:10.1016/0016-7142(87)90008-1.
Mouchet, J.P. and Mitchell, A. 1989. Abnormal Pressures While Drilling:Origins, Prediction, Detection, Evaluation. Paris: Elf EP-Editions,Editions Technip.
Osborne, M.J. and Swarbrick, R.E. 1997. Mechanisms for generatingoverpressure in sedimentary basins: a re-evaluation. AAPG Bulletin81 (6): 1023-1041.
Plumb, R.A. and Hickman, S.H. 1985. Stress-induced boreholeelongation: A comparison between the four-arm dipmeter and the boreholeteleviewer in the Auburn geothermal well. J. of Geophysical Research90 (B7): 5513-5521. doi:10.1029/JB090iB07p05513.
van Ruth, P., Hillis, R., and Tingate, P. 2004. The origin of overpressure inthe Carnarvon Basin, Western Australia: implications for pore pressureprediction. Petroleum Geoscience 10 (3): 247-257.doi:10.1144/1354-079302-562.
Ward, C.D., Mujica, D., and Ferrebus, C. 2003. Constraining Pore Pressurefrom Wellbore Failure Observations: examples from Venezuela. Presented at theAAPG International Conference, Barcelona, Spain, 21-24 September.
Zoback, M.D. 2007. Reservoir Geomechanics, 464. Cambridge, UK:Cambridge University Press.
Zoback, M.D. and Healy, J. 1984. Friction, faulting and in-situ stress.Annales Geophysicae 2: 689-698.
Zoback, M.D., Moos, D., Mastin, L., and Anderson, R.N. 1985. Well bore breakouts andin-situ stress. J. of Geophysical Research 90 (B7):5523-5530. doi:10.1029/JB090iB07p05523.