The relative reduction in both formation permeability and fracture flow capacity caused by the residue remaining after water based fracturing fluids are broken is often very important in the final selection of a fracturing fluid. Therefore, it is important to understand some of the factors which can affect the amount of residue produced from the gelling agents and the changes in relative flow which may result.
One of the most important factors in determining the amount of residue produced is the type of gelling agent used as a viscosifier. In general, the following order is commonly used as a guideline to determine the relative residue content of a number of gelling agents: guar gum > derivatized guar gum > derivatized cellulose.
Test results have shown that this relative order can be changed by varying the break time, breaker concentration, crosslinker and pH of the fluid system. For example, data has shown that a cellulose fluid can potentially cause more reduction to both fracture flow capacity and formation permeability than commonly used derivatized guar gelling agents.
The information which will be presented in this paper will contain results of an investigation into the effect of breaker concentration, breaker type, break time, crosslinker and pH of a fluid system on the relative flow reduction caused by a variety of water based fracturing systems. Fluids prepared with standard guar and cellulose gelling agents broken at low temperatures in a variety of porous media have been investigated. The importance of evaluating an entire fracturing fluid system and not just the specific gelling agent to determine which fluid should provide the optimum production increase from a hydraulic fracturing treatment will also be presented.