Wellbore Stability Modelling for Horizontal and Multibranch Lateral Wells in CBM: Practical Solution to Better Understand the Uncertainty in Rock Strength and Coal Heterogeneity

Abstract

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.

New Integrated History Matching Approach for Vertical Coal Seam Gas Wells in the KN Field, Surat Basin, Australia

“…Since the engineering factors have significant impacts on the gas production, , the production behavior of each well should be analyzed before conducting the history matching for the individual wells. It was found that most low producers used open annulus and gravel-packed completion types, and the abnormal low production at a particular period was usually affected by the unreasonable drainage working systems, such as a sudden decrease in BHFP and noncontinuous dewatering.…”

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…Coal fines are a common issue in almost all major CSG fields globally, such as in Bowen Basin (Australia), San Juan Basin (USA), Qinshui Basin (China), and Junggar Basin (China) . Coal fines are small particles released from the coal and mainly consist of nonorganic minerals like clay, kaolinite, quartz, and others. ,, They can be divided into two types: (i) primary coal fines, which refer to the coal fines that already exist before the production, and (ii) secondary coal fines, which are production induced. , More coal fines are observed during the dewatering and two-phase flow stages than in other stages, , as illustrated in Figure .…”

“…Coal fines are a common issue in almost all major CSG fields globally, such as in Bowen Basin (Australia), 201 San Juan Basin (USA), 202 Qinshui Basin (China), 203 and Junggar Basin (China). 204 Coal fines are small particles released from the coal and mainly consist of nonorganic minerals like clay, kaolinite, quartz, and others.…”