This paper describes how the fracture model for Ahmadi was incorporated into a single and dual porosity simulation model. It highlights the approach and methodology that has been used for understanding the reservoir connectivity and its drive mechanism. In addition, the effect of dual porosity model in improving the initial history match of the reservoir performance and its recovery mechanism has been studied.The two Ahmadi carbonate reservoirs in Bahrain Field (Aa and Ab) are thin, highly faulted and irregularly-fractured. The complexity of these reservoirs has prevented an efficient recovery with average production of wells to 15 Bopd. This has prompted a detailed integrated study to fully understand the recovery mechanism and to increase the wells' productivity.A conceptual model has been developed for the reservoir connectivity of Ahmadi reservoirs by integrating static and dynamic data. This comprehensive study that integrates transient welltesting and production data with cores and image logs to map fracture network derived using seismic facies has resulted in improving the understanding of reservoir connectivity and flow mechanism. This was accomplished by building Discrete Fracture Model (DFN) that was tuned and validated using sector local well test models to match KH and pressure responses.In order to reduce uncertainties in the model, different scenarios were built for different fracture intensity and aperture to derive appropriate parameters to pass to reservoir simulator for full field simulation. DFN model output was used in both single and dual porosity models to obtain production performance of the reservoirs.
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AbstractThis paper describes a creative and pragmatic approach that improved the production from one of the most difficult reservoirs in the Bahrain field. The Middle Cretaceous Ab zone is a thin, tight, highly faulted, and irregularly-fractured limestone reservoir. The difficulty with this 15 ft, 1 md reservoir has prevented an efficient recovery. The average production of wells is 15 bopd. This has prompted a detailed integrated study plan to increase the wells' productivity. Welltesting was key to understand the reservoir dynamics. A comprehensive welltesting campaign revealed a flow mechanism controlled by a fracture network. Fracture modeling and simulation failed to give clues on how to improve the productivity. However, the new approach that links transient welltesting and production data with fracture network indications derived from seismic interpretations has resulted in improving the productivity considerably. This was accomplished through re-entering old wells and designing special trajectories to intersect productive open fractures. The productivity was significantly increased to 60 bopd with sustained performance. The paper describes in detail our approach and methodology to understand the reservoir and its drive mechanism and to increase productivity and recovery starting from analyzing core data up to designing special configuration wells. The paper further highlights the pitfalls of the conventional workflow approach in modeling such difficult reservoirs.
This paper presents a new way to numerically simulate flow in Dual Porosity - Dual Permeability system which is solved rigorously with wellbore storage and skin. This paper shows that the use of Orthogonal Collocation method is feasible and that, in many cases, it results in solutions that are more realistic than those resulted from numerical inversion of Laplace transform. There are, however, certain disadvantages. For example, oscillation of the pressure derivative which can be overcome by using Orthogonal Collocation on Finite Element (OCFE) in which programming effort are usually in excess of that required by a finite- difference or numerical Laplace inversion scheme. Even so, it is felt that the potential of the technique is sufficient justification for this work and for a continuing effort to apply it to well test simulation problems.
Dual Porosity - Dual Permeability well testing problem is described by a complex set of nonlinear partial differential equations. Their solution is normally achieved analytically using Laplace transform or numerically through the use of numerical inverting methods of the Laplcace transform like Stehfest and Crump. This paper is an extension to the paper SPE 120668 that introduced the method for the basic well test problem.
The primary objective of this paper is to investigate the feasibility of using Orthogonal Collocation on well test in Dual Porosity - Dual Permeability system. Since this work was primarily concerned with the feasibility of Orthogonal Collocation simulation, no attempt was made to study a wide spectrum of cases of well test problems. However, a few typical applications are presented and some of the results are compared with those derived from analytical and numerical inversion.
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