Qi Qu

Water-Based Environmentally Preferred Friction Reducer in Ultrahigh-TDSProduced Water for Slickwater Fracturing in Shale Reservoirs

Currently inverse-emulsion polymers are the most popular friction reducers used in fresh water slickwater fracturing in shale reservoirs. The fluid volumes in fracturing treatments have increased substantially, while water supply has become more of a public concern. Rather than paying to treat and dispose of produced and flowback water, operators would like to reuse it in subsequent stimulation treatments. Produced water, especially from shale plays such as Marcellus and Bakken, is known for its high total dissolved solids (TDS) and high divalent cation content. This poses extreme challenges for current friction reducers because cations hinder the inversion of friction reducers and cause loss of efficiency of friction reduction to below 30%. Treating produced water to the quality suitable for conventional fracturing fluids is time-consuming and often costprohibitive. A salt-tolerant, water-based friction reducer was developed to address the challenges of high-TDS produced water. It was tested in a friction loop in a wide variety of produced water types from Bakken, Marcellus, Permian basin and other shale plays at different temperatures and was found to be highly effective. In a produced water sample with TDS over 300,000 ppm and total hardness as CaCO3 (TH) over 90,000 ppm as representative water, the new polymer hydrates within 10 seconds and gives a friction reduction profile similar to that of current inverse-emulsion friction reducers in fresh water. The fluid is compatible with other common stimulation additives such as scale inhibitors, biocides, clay stabilizers, surfactants, and breakers. The new friction reducer was also field tested in New Mexico using produced water with higher than 250,000 ppm TDS and 50,000 ppm total hardness as CaCO3, and head-to-head comparison with a conventional friction reducer under field conditions showed significant performance improvement in terms of pumping at much higher rates while maintaining much lower surface treating pressure. This paper will discuss the evolution of the technology and show friction reduction performance in various high-TDS water samples under lab conditions. Successful field test and comparison against conventional friction reducers are presented. The new friction reducer provides the oilfield industry a cost-effective solution of reducing produced water disposal and fresh water demands, thereby ultimately improving environmental impact of well operations.

Benefits of Novel Preformed Gel Fluid System in Proppant Placement forUnconventional Reservoirs

Post-treatment production analyses after hydraulic fracturing with crosslinked gel or slickwater often indicate that the treatment did not achieve the designed fractured area, which could be attributed to non-ideal proppant placement in the fracture. Although crosslinked gel provides good proppant suspension, it may not provide the desired proppant transport under downhole conditions. It is also difficult to clean up and thus induces gel damage into the proppant pack and formation. Slickwater treatment reduces gel damage, but proppant settling and banking problems can reduce the chance of achieving optimal fracture conductivity. Several proppant placement techniques have been developed to generate highly conductive paths for hydrocarbons to flow from an unconventional reservoir to the wellbore, such as hybrid fracturing, ultralightweight proppant delivery, and reverse hybrid fracturing. This paper demonstrates a novel fracturing fluid and its nearly perfect proppant transport characteristics. An engineered method of applying such fluids to optimize proppant placement and maximize fracture conductivity is discussed. The novel fracturing fluids are based on preformed gel fluids. When properly selected, the fluids can ideally suspend proppant under downhole conditions and carry all types of proppants into the fracture. This leads to better transverse and vertical placement of proppant in the fracture and significantly increases the fractured surface area, which is one of most important factors in unconventional reservoir production. The degradability of the fluid can be controlled by reservoir temperature, fluid pH, or breaker loading, which leads to optimized proppant pack conductivity. This paper discusses the evolution of the technology and laboratory testing results for this unique fluid system. The system has applications in areas requiring high fractured surface area and high regained conductivity, such as unconventional liquids-rich formations.