Leaching studies on Novolac resin-coated proppants-performance, stability, product safety, and environmental health considerations

Experimental Study on the Backflow Mechanism of Proppants in Induced Fractures and Fiber Sand Control Under the Condition of Large-Scale and Fully Measurable Flow Field

The proppant backflow in the process of flowback has a great significant effect on gas field development. Therefore, the study of proppant backflow is of great significance for the development and production of gas wells. At present, the physical simulation methods for proppant backflow mainly include the tube perforation model, the slot model, an API standard flow tester, and a large-scale flowback apparatus. The current experimental methods are unable to observe the backflow of proppants during the process of the flowback test. In addition, the only characterization parameter for proppant backflow is the liquid flow rate corresponding to the sand discharge in the diversion chamber called critical velocity, which is too simple and single to accurately characterize the movement state of proppants during the flowback process. In this paper, a physical simulation method of proppant backflow in fractures based on the measurement of flow field was proposed. It can realize the observation and fine description of the proppant backflow state and movement rule. In addition, the process of proppant backflow can be quantitatively described by a multidimensional characterization parameter. The research shows that (1) the proppant backflow is closely related to the shape of the sand bank formed during the proppant placement and the irregular voids formed; (2) the fiber increases the strength of the proppant pack significantly; (3) the critical velocity with fiber increased by 2.25 times compared with the critical velocity without fiber, the optimum fiber concentration was 0.8%, and the fiber length was 12 mm; (4) the full fiber injection was selected as the best injection mode by the experiment; and (5) the whole process of flowback can be divided into two stages. In the strong fluid shear stage, the effect of fiber sand control is more significant. However, when the flowback enters the stage of slow erosion, the difference in the sand control effect under different parameters is no longer significant.

Insight into thermo-mechanical enhancement of polymer nanocomposites coated microsand proppants for hydraulic fracturing

The present work reports the fabrication of ultra-high strength microsand proppants (100 mesh) through a polymer nanocomposite dual coating approach and gives insight into their thermo-mechanical reinforcements. The dual coating can be of 3D-cross-linked poly(styrene-methyl methacrylate)/divinylbenzene) (PS-PMMA/DVB) porous network and thermally cross-linked epoxy with graphene nanosheets. The inner layer of PS-PMMA/DVB was prepared using bulk polymerization of styrene (S) and methyl methacrylate (MMA) at 70 °C with a free radical initiator azobisisobutyronitrile (AIBN). The outer layer was prepared by mixing epoxy resin, a cross-linker, and commercial graphene (CG) followed by thermally curing the mixture. The dual-coated microsand proppants exhibited enhanced mechanical characteristics of elastic modulus (E) as high as 7.78 GPa, hardness (H) of 0.35 GPa, and fracture toughness (K_c) of 3.19 MPa m^1/2 along with largely improved thermal properties. Moreover, the dual-coated microsand proppants exhibit a very high-stress resistance up to 14000 psi, and to the best of our knowledge, this is the highest stress resistance value attained for the modified sand-based proppants so far.

Progress of Polymer Application in Coated Proppant and Ultra-Low Density Proppant

Design, synthesis and application of low-density proppant (LDP) are of great significance for efficient and clean exploitation of low permeability oil and gas. On the basis of a brief introduction of hydraulic fracturing and the application of traditional proppants, this review systematically summarized the polymer application progress in LDP, including coated sand, coated ceramics, coated nutshells, especially for polymer composites based ultra-low density proppant (ULDP). Finally, the existing problems and future development direction are also prospected.

Facile and Controllable Preparation of Poly(St-co-MMA)/FA Microspheres Used as Ultra-Lightweight Proppants

Hydraulic fracturing is an important technology for the exploitation of unconventional oil or gas reservoirs. In order to increase the production of oil or gas, ultra-lightweight proppants with a high compressive strength are highly desirable in hydraulic fracture systems. In this work, a new type of ultra-lightweight proppant, poly(styrene-co-methyl methacrylate)/fly ash (poly(St-co-MMA)/FA) composites with a high compressive strength were prepared via in situ suspension polymerization. The Fourier transform infrared (IR) and X-ray powder diffraction (XRD) analyses confirmed that the poly(St-co-MMA)/FA composites were successfully prepared. The morphology analysis indicated that the composite microspheres show good sphericity, and FA powder was evenly dispersed in the matrix. The apparent density of the microspheres was between 1 and 1.3 g/cm³, which is suitable for hydraulic fracturing. Furthermore, the compressive strength and thermostability were dramatically improved with the incorporation of FA, which could withstand high pressures and temperatures underground. The obtained poly(St-co-MMA)/FA composite microspheres are promising for application as an ultra-lightweight (ULW) proppant in oil or gas exploitation, which provides a new approach for the design of high performance proppants.

Biomimicry Surface-Coated Proppant with Self-Suspending and Targeted Adsorption Ability

Proppant is a key material, which can increase the production of unconventional petroleum and gas. Excellent proppants with a long migration distance are required in the fracture network. Resin-coated proppants have been confirmed as a good choice because of the long migration and the self-suspending ability in fracturing fluids. However, the distribution of the resin-coated proppants in fracture networks is random. The design of proppants with targeted adsorption is urgently needed. In this study, a novel proppant coated with a phenolic resin shell doped with Fe₃O₄ nanoparticles on ceramic (coated proppant) was designed and investigated. Based on the results, the coated proppant was adsorbed on the magnetic component's parts of the fracture network surface, which helps in enhancing the uniform distribution of the proppant in the fracture rock cracks. Meanwhile, the self-suspending ability of the coated proppant is five times higher than that of the uncoated proppant and can migrate a longer distance in the fracture network. Moreover, the liquid conductivity of the coated proppant is 30% higher than that of the uncoated ones at a closure pressure of 6.9 MPa. In summary, new insights into the design of functional proppants and further guidelines on the production of unconventional petroleum and gas have been provided in this study.