Abstract
Fracturing operations in tight reservoirs tend to be driven by efficiency and costs of the operations due to low reservoir quality and field development economics dictate the continuously increasing demand to deliver more stages within a short period of time. The objective of this paper is to revise and enhance fluid design parameters in high-temperature (HT) reservoirs by dealing away with fluid over-designing practices through accurate fracturing modeling which will significantly reduce reservoir damage.
Fluid design practices often assume a safety factor for the fluid exposure duration to be greater than the full treatment duration. It is also commonly required to match the bottom hole static temperature (BHST) for the whole lab test with a minor focus on the overall tubulars and reservoir cooldown during later stages of the treatment. The data frac results were then compared with the experimental lab condition in order to measure leak-off severity and cool-down dynamics in both scenarios. The result was injected into a detailed sensitivity analysis in order to come up with the optimum fluid design assumptions.
Advanced software modeling and rheological studies identified several ways to avoid fluids overdesign, leaving behind cleaner reservoirs without imposing operational risks. The sensitivity analysis revealed that depending on several parameters such as the fluids temperature at surface, volume and rate of the treatment; the safety factor applied in typical laboratory practice may reach up to 300% for some additives in the acid systems. This translates into additional challenges to formulate the fracturing fluid for excessive exposure periods, which as proven in lab experimental conditions, is not really required. Even more, the excess treatment chemicals create significant reservoir damage. The studies provided a workflow describing how and where fluid design can be tailored to reservoir conditions and a decision tree for fluid design in extreme HT formations.
This paper will reveal a modeling and experimental approach to optimizing assumed parameters of the fracturing and stimulation fluids and will help to shape the future of the treatments in HT reservoir conditions in a way that will not only reduce the fracturing cost but will also help to reduce reservoir damage hence improving well productivity.
