Wellbore Stability Modelling for Horizontal and Multi-Branch Lateral Wells in CBM: Practical Solution to Better Understand the Uncertainty in Rock Strength and Coal Heterogeneity
- Ratih Puspitasari (Schlumberger) | Thomas Gan (Arrow Energy) | Zachariah John Pallikathekathil (Schlumberger) | Joao Luft (Arrow Energy)
- Document ID
- Society of Petroleum Engineers
- SPE Asia Pacific Oil & Gas Conference and Exhibition, 14-16 October, Adelaide, Australia
- Publication Date
- Document Type
- Conference Paper
- 2014. Society of Petroleum Engineers
- wellbore stability, CSG, CBM, coal strength
- 2 in the last 30 days
- 274 since 2007
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Arrow Energy has engaged in drilling production Coal Bed Methane (CBM) wells in the Bowen Basin. As part of its field development strategy, varied styles of horizontal wells have been planned and executed along the coal targets of Moranbah Coal Measures (MCM). Some of the recently drilled multi-branch lateral and horizontal wells experienced different drilling challenges and production performance. Potential geomechanical issues such as borehole conditions and fines/solid production are directly related to wellbore stability during and post drilling.
As part of Arrow subsurface modeling strategy, the project has embarked a detailed Geomechanics study in Moranbah Gas field. The main objectives were aiming to: (i) optimize the mud weight that is required to stabilize the borehole, (ii) understand how specific coal targets respond to the induced stress concentration around the wellbore during drilling and, (iii) capture the vertical and lateral mechanical heterogeneity within specific coal seams. This paper focuses on practical solutions to model the borehole stability, in particular of the uncertainties in the rock strength modeling and coal heterogeneity.
This innovative workflow coupled with geostatistical approach of rock strength and insitu stress with depth-of-damage is first of its kind in CBM environment. Borehole collapse depth-of-damage (DoD) concept is then used to assess risk associated to the volume of yielded rock as a percent of borehole size. The higher the percentage of DoD, the higher the risk of producing excessive cavings. It provides more confidence in optimizing drilling mud weight for CBM horizontal wells by allowing a more scientifically-sound and practical solution to address rock failure mechanisms associated with borehole instability.
Arrow Energy has been extensively producing coalbed methane (CBM) from fields in the Bowen basin in central Queensland and the Surat basin in southern Queensland. One of Arrow’s main coal targets in the Bowen Basin is the Moranbah Coal Measures (MCM) of late Permian Age (Fig. 1). The MCM is part of the Blackwater group, and it is best developed along the western margin of the northern Bowen basin. The MCM contains multiple coal seams generally ranging in thickness from 2 to 5 m but up to 10 m in some areas, with cumulative thickness of up to 25 m. A typical log profile and coal properties in the MCM are shown in Fig. 2. The MCM seams exhibit favorable CBM reservoir properties with wells yielding good production rates through surface-to-inseam drilling and hydraulic fracturing completion techniques.
As part of the field’s development strategy, varied styles of horizontal wells have been planned and executed along the coal targets of MCM. Some of the recently drilled multibranch lateral and horizontal wells experienced different drilling challenges and production performance. Potential geomechanical issues such as borehole collapse, drilling challenges, and fines/solid production are directly related to wellbore stability during and after drilling.
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