Introduction

Probabilistic evaluation

In this stage, the uncertainty overlooked in stage 1 is considered and evaluated. Each fixed parameter in the previous stage is now given an initial distribution (Table 1). Correlation between porosity and saturation was assumed to be a positive correlation, and that between the fracture numbers and fracture half-length was assumed to be a negative correlation. Next, a simulation was performed to refine the assumed distribution and to forecast the possible production. The initial and final distribution of the parameters is summarized in Table 1. Figure 7 shows P10, P50, and P90 forecast for Well 1 and Well 2. Fracture networks and fracture number are two of the major parameters that affect gas production from shale gas reservoirs.

Table 1 Initial and final distribution of uncertain completion parameters

Parameters Initial distribution Final distribution
Distribution type Min Max Mean Distribution type Mean P10 P90
Number of fractures Triangular 32 63 48 Normal 47 57 38
Fracture half-length (ft) Uniform 30 250 – Log-normal 118 208 46
Fracture conductivity (N/A) Uniform 5 300 – Normal 21 32 16
Inner permeability Uniform 90 400 – Log-normal 162 290 117
Outer permeability Uniform 20 90 – Log-normal 25 34 20




Fig. 7

Forecasted Normalized Gas Rate Versus Normalized Time (Semi-Log Scale)