Abstract Exploration and development of coalbed methane (CBM) reservoirs is ongoing in the Asia Pacific region, with low permeability, undersaturated coals being the target in some areas. Horizontal wells are typically required to produce low permeability CBM reservoirs at commercial rates, and may experience a period of single-phase (water) transient flow, followed by a transition to two-phase (water + gas) transient flow. Wells exhibiting this behavior are particularly difficult to model analytically, yet simple analytical and semi-analytical tools are desirable for making quick, but reasonably accurate forecasts. The purpose of this work is to therefore provide a new forecasting methodology for low permeability, undersaturated CBM wells. The new method for forecasting CBM wells introduced in this work is based on the concept of a dynamic drainage area (DDA), recently adapted to forecast tight black oil and gas condensate wells exhibiting two-phase flow. A critical advancement provided in the current work is modeling the transition from single-phase flow of water to two-phase flow of gas and water during the transient linear flow period, which was not attempted for the black oil/gas condensate cases. Above desorption pressure, material balance, performed on the dynamic drainage area to determine average pressure in the distance of investigation, is combined with the linear flow productivity index equation to forecast water production at each time step. For two-phase flow below desorption pressure, the two-phase version of the linear productivity equation and material balance equations for water and gas are solved iteratively for pressure, saturation and fluid production rate within the DDA. The gas material balance equation accounts for desorption effects. In order to calculate the DDA at each time step, the linear flow distance of investigation equation is used. Importantly, using the DDA method, variable operating conditions (flowing pressures) may be accounted for, which is critical for CBM wells during early stages of production. The new semi-analytical DDA model is used to history-match production data from an actual horizontal well completed in a low permeability, undersaturated, western Canadian CBM reservoir. Further, the match is compared to that obtained from rigorous numerical simulation. The history-match of the field data is reasonable with the new model and comparable to numerical simulation. The new model is however easier to setup and less data-intensive than numerical simulation, providing a practical alternative to CBM reservoir engineers who are responsible for generating a large number of forecasts.
[1]
Y. Meng,et al.
Modeling transient flow behavior of a horizontal well in a coal seam
,
2012
.
[2]
Thomas Gentzis,et al.
The use of numerical simulation in predicting coalbed methane producibility from the Gates coals, Alberta Inner Foothills, Canada: Comparison with Mannville coal CBM production in the Alberta Syncline
,
2008
.
[3]
C. Clarkson,et al.
Transient flow analysis and partial water relative permeability curve derivation for low permeability undersaturated coalbed methane wells
,
2015
.
[4]
T. Gentzis,et al.
Coalbed methane producibility from the Mannville coals in Alberta, Canada: A comparison of two areas
,
2008
.
[5]
Ahmed H. El-Banbi,et al.
Production Analysis of Linear Flow Into Fractured Tight Gas Wells
,
1998
.
[6]
Christopher R. Clarkson,et al.
Optimization of CBM Reservoir Exploration and Development Strategies through Integration of Simulation and Economics
,
2005
.
[7]
Christopher R. Clarkson,et al.
Impact of Distance-of-Investigation Calculations on Rate-Transient Analysis of Unconventional Gas and Light-Oil Reservoirs: New Formulations for Linear Flow
,
2015
.
[8]
C. Clarkson.
Case Study: Production Data and Pressure Transient Analysis of Horseshoe Canyon CBM Wells
,
2009
.
[9]
Paul S. Schafer,et al.
A guide to coalbed methane reservoir engineering
,
1996
.
[10]
C. Clarkson,et al.
History-Matching and Forecasting Tight Gas Condensate and Oil Wells Using the Dynamic Drainage Area Concept
,
2015
.
[11]
Christopher R. Clarkson,et al.
Production-Data Analysis of Single-Phase (Gas) Coalbed-Methane Wells
,
2007
.
[12]
A. Ibrahim,et al.
A comprehensive model to history match and predict gas/water production from coal seams
,
2015
.
[13]
Louis Mattar,et al.
A Physics-Based Method for Production Data Analysis of Tight and Shale Petroleum Reservoirs Using Succession of Pseudo-Steady States
,
2014
.
[14]
Randahl Dean Roadifer,et al.
Coalbed Methane Pilots--Timing, Design, and Analysis
,
2009
.