FAST Optimization of Line-drive Water Injection

Abstract The Halfdan Field has been developed with long parallel horizontal wells using alternating producer/injector pairs (Figure 1). Using the Fracture Aligned Sweep Technology (FAST) the injectors were hydraulically fractured along the wellbore to increase injectivity and enhance the sweep geometry. The anticipated FAST fracture orientation has been verified by 4D seismic interpretation and confirms the geomechanical concept of FAST. As reservoir pressure increases the fractures tend to close. This provides an opportunity to further increase injection pressure. However, the risk of extending the fracture into the Halfdan spine wells makes it necessary to increase injection pressures in a controlled manner. This paper provides a method to operate water injection at the field's performance limit. The following tools have been applied, further developed and confirmed by field data. Fall off testing to Estimate Current Fracture Heights: Analysis of more than 200 falloff tests to estimate fracture height and to identify opportunities for increased injection rates. Step Rate Tests to Increase Injection at Unchanged Fracture Height: Execution and analysis of more than 60 Step Rate Tests to increase injection rates at constant fracture height. Controlled Fracture Criterion to Control Fracture Propagation: Development of correlations for fracture height vs. injection pressure and fracture opening pressure vs. voidage to identify performance limits and improve the control of the fracture propagation. An average pressure gain of 80 psi per injector corresponding to a total of 8,000 bbl/d of injected water has been achieved for the 26 Halfdan water injectors. The incremental oil gain from this is estimated at 3,500 bbl/d. Better fracture height control and propagation, securing reserves by lowering the risks of producer-injector short circuits, has been achieved through an improved understanding of fracture behavior from fall off tests and correlation between pressure, rates and voidage. This method has successfully been applied at field scale with proven results and is refined with the acquisition of new field data.