A Practical Numerical Model to Optimize the Productivity of Multistage Fractured Horizontal Wells in the Cardium Tight Oil Resource

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Abstract
The technology to multi-stage fracture horizontal wells has opened up development of tight hydrocarbon resources world wide. One such resource in Canada is the Cardium Formation which extends over 3.5 million acres and has an estimated OOIP of over 10 billion barrels. The new technology has allowed accessing these tight resources which were previously uneconomic to develop with vertical wells. For the Cardium it is particularly true for the halo (or periphery) where reservoir quality was insufficient for economic depletion with vertical wells. This paper demonstrates an efficient model and methodology to optimize multi-stage fractured horizontal wells and provides production forecasts. A quarter of a fracture numerical simulation method (Quarter-Frac Model) with multi-phase and multi-dimensional characteristics is utilized in this paper to simulate the fluid flow from the repetitive drainage element in a full field development. The model uses an accurate description of the reservoir in terms of geology, fluid characteristics, and pressure profile. The overall performance of the multi-stage fractured horizontal well is determined by a range of completion variables that include well spacing, fracture spacing, fracture dimensions and characteristics, and placement of first and last fracture. The simulations are carried out for a range of completion and development variables. The results are then translated into the performance of the whole horizontal well. The optimum completion and development scenario depends on economic considerations. It is realized that the first and last fractures (toe and heel) will have different drainage areas compared to those of the inside fractures. This is demonstrated by comparing the Quarter-Frac Model to an All-Frac Model simulating an actual horizontal well length with multiple fractures simulated with local grid refinement. A penetration ratio is introduced that describes the effect of placing fractures nearer to the section boundaries. The quarter-fracture model is shown to be efficient and provides reservoir engineers with a practical and accurate tool to design and optimize multi-stage fractured horizontal wells. The quarter-fracture model has applications for primary and secondary recovery. Simulation results for the Cardium Formation have shown rapid pressure decline with primary depletion in full field development. An improvement in recovery can be achieved with pressure maintenance. Some preliminary simulation results are provided that show the effect of water injection which will be piloted in the field to demonstrate the feasibility.

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