For low permeability formations like oil and gas bearing shales, hydraulic fracturing stimulation is a requisite to obtain commercial production. One of the key parameters for ensuring successful stimulation and prolonged production is the right selection of stimulation fluid. The selection and optimization of the fracturing fluid is greatly dependent on the reservoir rock properties as well as the formation softening due to fluid-formation interaction. A slick water treatment fluid has often been adopted in tight shale plays in the past for creating a complex fracture network for maximum production yield. Most often the slick water recipe is driven by formation fluid sensitivity analysis, e.g., effect of fresh water, salt or acids on formation. While this may work for some formations, the rock mechanical properties such as Young’s Modulus and Poisson’s ratio will determine the fraccability and whether it is advantageous to use a slick water, linear gel, or crosslinked gel. Similarly, analysis of formation softening with Brinell hardness testing and proppant embedment testing will help ensure that the formation does not close upon treatment completion and will have conductive flow channels. This paper discusses the impact of different types of fracturing fluids on different shale formations. The paper also describes test processes involving fluid sensitivity tests, formation softening, and rock mechanical tests and compares data from a few representative shales to show the impact of choosing the right fluid formulation for hydraulic fracturing. The formation rock, proppant, and fracturing fluid interaction may also result in diagenetic growth on proppant and formation faces resulting in formation softening and large decrease in fracture conductivity. The paper focusses on careful optimization of the stimulation fluid based on rock parameters to ensure prolonged production in tight oil and gas shale plays.
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