Maximizing Fracture Conductivity with Proppant Partial Monolayers: Theoretical Curiosity or Highly Productive Reality?

Abstract

Abstract Hydraulic fracturing practitioners have long theorized that maximized fracture conductivity could be achieved by creation of fractures with partial monolayers of proppant. Fracturing mechanics and design experts have lamented that fractures filled with partial monolayers of proppant, while highly desirable, were "virtually impossible to achieve". The expert's reasoning was expressed as due to the inability to obtain uniform and complete coverage of the fracture with a partial monolayer, insufficient proppant strength to support the load, loss of fracture width due to proppant embedment and, potentially deleterious non-Darcy flow effects in the relatively narrow propped fracture. Many innovative fracturing products and design techniques have recently been developed and introduced to cost efficiently enhance well productivity. Evaluation of case histories of several wells recently treated utilizing some of these innovations have led to the consideration that perhaps the experts were a bit too hasty. Slickwater fracturing has enjoyed a recent renaissance, in large part, due to the favorable treatment cost economics for the well stimulation benefit achieved using such non-damaging, low viscosity fluids. Slickwater fracturing treatments have historically been typified by pumping large volumes of slickened water at high rate to deploy relatively small volumes of frac sand. A potential shortcoming of slickwater fracturing treatments is the tendency for fracture propagation out of zone due to the high treating rates and, proppant settling below the target zone due to the poor transport properties afforded by the low viscosity treating fluid. Optimization of slickwater fracturing treatments employing recently developed ultra-lightweight proppants to facilitate proppant placement throughout the entire created fracture area has found success. Wells treated with the new proppants using refined placement techniques have been observed to experience extraordinary stimulation increases which are indicative of production through a partial monolayer proppant pack. The observed increases are resulting in payouts in a few weeks or months compared to the years experienced historically with previous methods. The focus of this effort will be a review of case histories of wells treated with new products and placement techniques. Discussion of slickwater treatment design optimization and laboratory evaluation of the ultra-lightweight proppant partial monolayer conductivity and transportability is also provided. Results demonstrate how merging new technologies with old techniques can produce modern, high value results. Introduction and Background Hydraulic fracturing may be characterized as a complex process involving pumping highly pressurized fluid into a well at a rate sufficient to create fractures in a subterranean formation. The fractures provide highly conductive flow paths radiating laterally away from the wellbore, and thereby, a means to increase the productivity of an oil or gas well completion. Proppants are typically placed in the fracture to ensure that the created flow path remains open and thus, conductive, once the treating pressure is relieved. Since the first "hydrafrac" treatment in 1947, hydraulic fracturing has become recognized as a key process in the enhancement of petroleum recovery1. Over the past fifty-some years, the industry has directed substantial resources toward gaining greater understanding of the mechanics of fracturing processes and, to the ongoing evolutionary improvement of equipment, products, and techniques to optimize the productive benefits of hydraulic fracturing application.