Selection of Diverter for Refracturing in Hydrocarbon Bearing Formations

Abstract

The application of chemical diverter is an evolving technology and has become popular among E&P operators especially during refracturing treatment. The primary objectives of diverter application are uniform distribution of treatment slurry within the target zone to increase stimulated reservoir volume (SRV); treat unstimulated and under-stimulated zones; reduce the treatment time by decreasing the number of stages; increase fracture density by creating complex fracture network; and prevent fracture interference between adjacent wells. Diversion of treatment fluid is the major attribute of successful refracturing treatment. This presents challenges with respect to selection of diverter chemical, particle size distribution, proportions of diverter and proppant, and total quantity of diverter. The advantages of chemical diverters are simple injection without any pumping system modification and negligible increase in treatment time. Their chemical composition can be tailored according to the reservoir properties. The mixture of powder and flakes are employed for Near Wellbore Diversion (NWD) application to develop temporary bridge at pre-existing fractures. The mixture of chemical particulates in the powder form and proppant is applied for Far-Field Diversion (FFD) to redirect fluid far in the formation by (restricting fracture extension) to develop additional fractures. Several diversion mechanisms are illustrated for various applications. The diverter works on jamming and sealing mechanism. These mechanisms are investigated in the laboratory by performing plugstability experiments on simulated perforations and fracture. This helps in optimization of parameters such as particle size distribution, minimum diverter concentration and proportions of various sized particles for different applications. The viii behaviour of pressure build-up and leakoff are compared to evaluate a variety of diverter blends. The effect of flakes is also evaluated. An empirical model is developed based on dimensional analysis to estimate pressure differential when fluid flows through a diverter pack. The diagnostic tools such as pressure monitoring, microseismic, tracers and fiber optic techniques are also illustrated in detail to analyze and understand the effectiveness of diversion. This research accentuates on establishment of novel methodology to evaluate performance of diverter for NWD and FFD applications. It will aid in development of industry standard procedure for the evaluation of diverter performance. The primary focus of this research is on the selection parameters for near-wellbore diversion application but also throws light on the selection parameters for far-field diversion. This research will advance the state-of-the art chemical diversion technology and ultimately improve the effectiveness of refracturing treatments. Significant insight into the diversion technology and guidelines for its successful application are provided to help engineers to increase the effectiveness of refracturing treatments.