Development of liquid rich shale (LRS) reservoirs has gained tremendous momentum in recent years. A detailed understanding of fluid behavior, completion practices and reservoir dynamics is essential to accurately predict their long-term performance. This paper uses stochastic reservoir modelling to identify the optimal values for several completion and uncertainty parameters.
A compositional reservoir simulation model for a typical gas condensate well in the Eagle Ford shale was used to identify the optimal production strategies for maximum EUR of oil and gas. The important factors considered for the study are fracture spacing, fracture conductivity, fracture half-length, well spacing, porosity, permeability, initial GOR and well constraints. These factors are often studied independently of one another and their interaction is usually ignored. For example, in a higher permeability play, greater fracture density leads to rapid recovery but ultimate cumulative production does not improve. However, for a play with lower permeability, greater fracture density improves both recovery rate and EUR thereby leading to improved overall economics. Thus, interaction effects due to coupling can have a decisive effect on the overall performance of a reservoir. This paper presents a statistical study of both independent and coupled effects on ultimate oil and gas production from a LRS gas condensate reservoir.
The results show that fracture half-length and fracture spacing have the most complex and significant effects on performance of the reservoirs studied. High initial rates are often preferred in unconventional reservoirs with their rapid rates of decline. These high rates can be achieved with larger fracture half-lengths and smaller fracture spacing. This study shows that high initial rate of production leads to a greater liquid dropout and larger condensate banking. These results also reduce the production rate of gas due to relative permeability effects. Return on investment is reduced due to reduced cumulative production and excess spending on fracture creation. Similar effects were observed for other factors like well constraints where higher minimum flowing bottom-hole pressure led to lower cumulative gas production and lower liquid dropout. In some cases higher bottom-hole pressure might be preferable due to the differential in the price of condensate and gas.
The sensitivity studies in this study provide considerable insight into the long-term production behavior in LRS gas condensate reservoirs. During the initial phase of a project, uncertainties related to various field parameters and their coupled effects are often ignored leading to suboptimal returns on investment.