Abstract
Horizontal well completion and stimulation technologies are the keys to successfully develop shale gas reservoirs. The impacts of hydraulic fracture parameters, hydraulic fracture induced complex natural fracture system, and rock characteristics to well performance need to be clearly understood. Numerical simulation based methods provided a better way over other conventional methods for modeling well performance in shale gas reservoirs. However, current numerical simulation methods, dual porosity modeling and discrete modeling, have following limitations: 1) time-consuming in setting up hydraulic and natural fracture systems; 2) large computation time required.
We developed a new methodology to simplify hydraulic and natural fracture systems. Since large variations in natural fracture distribution and reservoir characteristics may result in unpredictable complex fracture network that cannot be accurately represented by discrete modeling, the hydraulic fracture and hydraulic fracture induced complex natural fracture system are treated as one enhanced zone. The simplified coarse dual porosity simulation model enables us to evaluate the effectiveness of stimulation treatment and understand shale gas production mechanism in a short time. To validate the new methodology, simulation results of a fine-grid reference model were compared with the simplified model. The simplified model greatly decreases simulation time and provides accurate results.
We applied this methodology to Haynesville shale gas wells. Historical gas production and flowing BHPs were matched. Reservoir and enhanced zone parameters were obtained after history matching, including porosity and permeability of the matrix and natural fracture system, half length, width, and permeability of the enhanced zone, as well as EUR. Simulation results indicate that if conductivities of enhanced zones are in same order shorter enhanced zone is corresponding to sharp production decline, while long enhanced zone is corresponding to relatively slower production decline. Conductivity of enhanced zone is the controlling factor for early time production performance and behaviors of flowing BHPs, while Matrix permeability and SRV half-length are the controlling factors for late timeproduction performance. Sensitivity analyses then were conducted to quantify the impact of the reservoir characteristics and enhancedzone parameters. The simulation results provided insights into effective stimulation designs and flow mechanism for shale gas reservoirs.
