A Practical Methodology for Production Data Analysis in Carbonate Reservoirs Using New Decline Type Curves

Abstract

Carbonate reservoirs typically have complex pore structures, so the production wells typically have high production in the early production stage, but they decline rapidly. It is highly challenging to achieve accurate interpretation results. In this paper, a new and practical methodology for production data analysis of fractured and fractured-vuggy carbonate reservoirs is proposed. Firstly, analytical solutions to characterize the different multipore media and simulate transient production behavior of fractured and fractured-vuggy carbonate reservoirs during the transient flow regime are presented. Then, a new function f q D and f ′ q D that related to the dimensionless production rate is introduced, and a series of new decline type curves are drawn to make a clear observation of different flow regimes. In addition, the effects of the storativity ratio, interporosity flow coefficient, skin factor, and dimensionless radial distance of external boundary on production performance are also analyzed. Finally, two example wells from the fractured and fractured-vuggy carbonate reservoirs are used to perform rate decline analysis with both the Blasingame type curves and the new type curves. The validation of the new method is demonstrated in comparison to the results of well test interpretation. The results show that the curves of 1 / f ′ q D vs. t D are ∧ -shaped for dual-porosity reservoirs and M -shaped for triple porosity reservoirs and also indicate that the interpreted parameters such as permeability, skin factor, storativity ratio, and interporosity flow coefficient using new decline type curves are aligned well test interpretation. In correlation with other traditional well test analysis, this approach effectively reduces the multisolution probability of interpretation.

Practical Semianalytical Models for Pressure-Transient Analysis of Carbonate Reservoirs with Complex Fracture and Cave Distributions

“…Fracture-caved reservoirs have great development potential in carbonate reservoirs and are gradually becoming the focus of carbonate reservoir development. − As the demands for crude oil increase, the development of fracture-caved reservoirs is becoming an increasingly important field in energy production. − Fracture-caved reservoirs exhibit high heterogeneity due to the fractures and meter-scale caves located in the different distributions. − The large-scale caves offer ample storage space while fracture zones with higher conductivity enhance the fluid flow efficiency. − The flow behavior will be affected by the location of wells and the distribution of caves in the formation. − The complex wellbore–fracture–cave distributions and flow mechanism characterization are not clear in previous studies. Therefore, there is an urgent need to develop transient models suitable for various fracture-caved distributions.…”

Novel Approach for Rate Transient Analysis of Fractured Wells from Carbonate Reservoirs with Heterogeneous Natural Fractures

“… 20 − 22 However, the Blasingame method is unsuitable for well productivity evaluation during the transient flow stage. 23 In addition, the formation is not divided into several regions to capture the heterogeneities in these models. 24 Numerical models can accurately simulate complex fracture geometries and reservoir heterogeneities for fractured well productivity evaluation and prediction in unconventional reservoirs.…”

“…The second type of method is based on analytical and semi-analytical models. In these models, the type of fracture is divided, and the distribution characteristics of the fracture and matrix systems are summarized. − Because of the simplicity of the mathematical formulation, the Laplace transformation is commonly used to derive the solution of these models, and type curves plotted by Blasingame are mainly used to conduct rate decline analysis for wells in various kinds of reservoirs. − However, the Blasingame method is unsuitable for well productivity evaluation during the transient flow stage . In addition, the formation is not divided into several regions to capture the heterogeneities in these models .…”