Front-End Engineering Studies for Carbonate Stimulation Optimization

This paper describes an integrated approach to stimulation treatment design for carbonate reservoirs. Using this process helps ensure that appropriate candidates are stimulated with the optimum treatment. Historically, many of the steps described have been applied in sandstone reservoir stimulation, but industry has lagged in the application of these technologies to carbonate reservoirs.

The discussion begins with preliminary candidate selection based on estimated productivity gains from various stimulation options. Well history and formation data is reviewed to evaluate near-wellbore damage and identify possible fluid-formation compatibility issues that will affect treatment choices. Productivity analyses indicate formation flow capacity, which can then be used to rank potential treatment options such as comparing the expected results from a matrix treatment to an acid fracturing treatment.

Core testing demonstrates that specific carbonate "rocks" will have uniquely different reaction characteristics when treated with various acid systems. This is a valid design consideration, whether the proposed treatment is matrix or fracture acidizing. This paper reviews the specialty core testing programs which are used to optimize acid treatments and present illustrative data.

All the previously-gleaned data provide inputs to selection of the most appropriate approach to stimulation and set the stage for the final design. In matrix treatments, the biggest challenge is often fluid placement and diversion. Fluid placement modeling, which also predicts skin reduction and stimulation results, is critical to evaluate the potential effectiveness of a possible treatment. When fracture acidizing is required, the same data can be used to refine the treatment design and provide more realistic simulation of the expected well response.