Abstract
In this study, a hydro-geomechanical coalbed methane reservoir characterization workflow was applied to multiple multilateral wellbore stability cases from the same coalseam formation. The data from core studies and borehole geophysical logging was integrated to create a full field hydro-mechanical earth model. The models were then used for uncoupled reservoir geomechanical simulation. The uncoupled simulations results were history matched against observed gas and water production rates. The initial and evolved stress tensor from the simulation was used to provide insight into observed horizontal CBM wellbore stability issues including borehole: initial failure, fines generation, and failure during depletion.
1. INTRODUCTION
Coalbed methane (CBM) in the Western Canadian Basin in Alberta has been identified as a major resource that can add to Canada's energy economy by filling part of the gap left by declining conventional gas reserves. In Alberta, the CBM industry has gone from relatively little activity prior to 2003 (less than 100 wells drilled per year), to more than 18 000 total wells as of 2012 being drilled for CBM, with some wells are comingled gas wells [1].
In the Mannville coal formations, production rates in vertical wells are typically less than 3000 m3/day. However, some successful horizontal wells have gas production rates greater than 12,000 m3/day. Based on historic data, economic viability of methane extraction from the Mannville formation is believed to be possible only through the drilling of horizontal wells, which provide greater connectivity to the coal reservoir surface [2]. Horizontal wells have been used extensively in the United States for CBM development, but transfer of technologies from the USA to the Mannville formation in the Western Canadian Basin has not been as successful as originally expected.
Several reasons for the limited success of horizontal wells production have been postulated, with geomechanical effects being included. The list of geomechanical effects includes: high stress fields, high stress anisotropy, weak coal, and coal natural fracture (cleat) closure
