Abstract
Fracturing fluids diversion has played a crucial role for maximizing well productivity in multistage fracture wells. Proper sizing and material designs of diverting agents are key elements to effectively bridge and plug perforations and fractures during treatment. In this study, we present improved designs of the water-soluble diverting agent that can cover a range of fracture widths. Also, a wellbore flow model that predicts swelling and dissolution behaviors of the diverting agents flowing from the surface to the fractures are developed for field applications.
Butene-diol vinyl alcohol co-polymer (BVOH) which has elastic and sticking properties in water is used as diverting agents. The cylindrical pellets and smaller size powder made from the polymer are mixed to bridge and plug hydraulic fractures. Using a HPHT filtration apparatus, BVOH diverting agents are evaluated for slit widths of 1 to 4 mm with different pellet geometries. The swelling and dissolution rates depend on many parameters such as temperature, dissolution time, crystallinity degree, and its geometry. In this work, empirical correlations that predict swelling and dissolution rates of BVOH polymers for various formulations were developed and implemented to the wellbore flow model that simulates fluid flow and heat transfer during pumping operations. A case study of a multistage hydraulic fracturing treatment is also presented to demonstrate applicability and effectiveness of the treatment.
The filtration test results with various diverting agent designs indicate that the length and diameter of the pellets affect the performance and effectiveness of bridging and plugging fracture-like slits. Moreover, the optimum pellet size exists for different slit sizes. With modified pellet size and diameter ratios, wider slits of 3 to 4 mm can be effectively plugged by the diverting agents with reduced leakoff volumes. The swelling and dissolution models show very good matches to the experimental data taking into account temperature, dissolution time and crystallinity degree. The case studies presented in this work illustrates that the models can predict the time required for the diverting agents to dissolve under field conditions and determine if the diverting agents pumped into the well provides sufficient conditions for diversion. Also, the study results indicate that the pump rate and injection conditions prior to pumping the diverting agent are key controlling factors in determining downhole temperatures and thus affect the time required for the degradation of the diverting agent. In addition, a field case study is also presented to demonstrate the effectiveness of the swellable, BVOH diverting agent in low downhole temperature, hydraulic fracturing treatment in the Permian Basin.
The swelling diverting agents exhibit more elastically than existing particulate diverting agents. The swelling polymers are less abrasive and thus reduces risks of equipment damage during preparation and pumping. The wellbore flow simulator developed in this study helps stimulation engineers optimize material types, particle size distribution, and concentration of the diverting agents for various field applications.
