Low-density Proppants Research Articles

Experimental Study on Proppant Migration in Fractures Following Hydraulic Fracturing

Complex fracture technology is key to the successful development of unconventional oil and gas reservoirs, such as shale. Most current studies focus on how to improve the complexity of the fracture network. It is still unclear whether proppant can enter the branch fractures at all levels after the formation of complex fractures. The effects of construction displacement, proppant particle size, proppant density, fracturing fluid viscosity, sand ratio, and other factors on proppant migration in single fractures and complex fractures were studied using an experimental device independently developed by the laboratory. The results show that the lowest point height of the sandbank and the equilibrium height of the sandbank are directly proportional to the particle concentration and density, respectively, and inversely proportional to the displacement and fracturing fluid viscosity. The equilibrium time of the sandbank is inversely proportional to the displacement, particle concentration, and density, respectively, and proportional to the viscosity of the fracturing fluid. Under the same experimental conditions, the larger the branch angle, the smaller the height of the main/secondary fracture sandbank. In the design of the fracturing process, fracturing fluid with varying viscosities and proppant with different densities should be selected according to the formation conditions and fracturing targets. In the face of long fracture lengths, the combination of low-viscosity fracturing fluid with an appropriate viscosity and low-density proppant can meet the goal of placing proppant over long distances and effectively supporting fractures over extended lengths. Subsequently, high-density proppant or reduced construction displacement are adopted to usefully support fractures in the near-wellbore area. The results of this paper can provide theoretical support for proppant selection and fracturing program design.

Numerical simulation of proppant transport from a horizontal well into a perforation using computational fluid dynamics

With the increasing global demand for oil and gas, the development of unconventional resources such as shale gas is becoming ever more important. The key to developing unconventional oil and gas resources lies in horizontal wells with multistage fracturing technology. In the process of horizontal well segmentation fracturing, the distribution of the proppant among multiple clusters has a significant influence on the fracturing effect. However, the influence of various factors on the entry of proppant into the perforation and then into the fracture along the wellbore is unclear. In this paper, based on the flow characteristics of proppants in fracturing fluids, we investigate the wellbore–perforation proppant transport using a Eulerian multiphase flow model. The effect of different factors on proppant entry into the perforation in horizontal wells is studied. We first verify that the computational fluid dynamics model satisfies the accuracy requirements for studying the sand-carrying efficiency of proppants in a perforation cluster. Second, the effects of the proppant size, proppant density, fracturing fluid viscosity, perforation diameter, and fracturing fluid flow rate on the proppant transport efficiency are investigated. Finally, a mathematical model of the sand-carrying efficiency is established by multivariate nonlinear fitting. The results show that the proppant size has a more significant effect on proppant settling at low wellbore flow rates. Increasing the diameter of the proppant particles can accelerate proppant settling. Higher wellbore flow rates tend to reduce the sand-carrying efficiency, although using a low-density proppant can mitigate the effect of the wellbore flow rate. At low wellbore flow rates, increasing the perforation size makes it easier for the proppant to enter bottom perforations. Increasing the fluid viscosity helps to distribute the proppant evenly between perforations in different directions, but this effect diminishes as the flow rate increases. Finally, a formula for the wellbore sand-carrying efficiency is obtained and validated, providing a basis for optimizing the distribution of the proppant in the perforation. The results from this paper enhance our understanding of the sand and fluid feeding patterns of each perforation cluster and provide direction for improving the construction process and enhancing the fracture inflow capacity.

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.

Proppant Transport Characteristics in Tortuous Fractures Induced by Supercritical CO2 Fracturing

Supercritical CO2 fracturing is an important development trend to reach the goal of "dual carbon" and avoid the problem that hydraulic fracturing is influenced by water resource. In order to clarify the transport characteristics of proppant in the fractures induced by supercritical CO2 fracturing, this paper reconstructs the fracture surface of rock samples after supercritical CO2 fracturing using the laser morphological scanning technology, and establishes a model of proppant carrying and transport of supercritical CO2 in tortuous fractures on the basis of CFD-DEM method. In addition, the transport and placement characteristics of proppant in tortuous fractures are analyzed by comparing with flat fractures, and the effects of proppant density, injection rate of proppant carrying liquid, proppant concentration and other key parameters on proppant transport and distribution in fractures are investigated. And the following research results are obtained. First, compared with those in flat fractures, the flow paths of the proppant carrying supercritical CO2 liquid in tortuous fractures are tortuous and diverse, and the proppant presents stronger fluctuations and jumps laterally and vertically during its transport. Second, the proppant placement in tortuous fractures morphologically presents a wavy or even clustered non-uniform distribution. Third, low-density proppant has a better pass-ability in tortuous fractures, and the high injection rate can reduce the influence of tortuous fracture structure on proppant blocking. Fourth, if the concentration of injected proppant in the tortuous fracture is too low, good fracturing support effect cannot be achieved, and the optimal value under the simulation conditions in this paper is around 3%. In conclusion, the simulation results are of important theoretical and engineering significance to understanding the mechanism of proppant blocking in the pumping process of proppant carrying liquid for supercritical CO2 fracturing and optimizing the field fracturing design.

Solidification and utilization of water-based drill cuttings to prepare ceramsite proppant with low-density and high performance

Water-based drill cuttings (WBDC) and bauxite are used as raw materials to prepare proppants with low density and high performance. The effects of sintering temperature, sintering period, mixture ratios of materials, doping with iron oxide, and acid modification of WBDC on the properties of proppants are discussed. The proppant performance is evaluated according to the national standard SY/T5108-2014. The morphology of the proppant is analyzed using scanning electron microscopy (SEM). The crystal phase structure of the proppant is studied using X-ray diffraction (XRD). Thermal analysis of the proppant sintering process is performed using thermogravimetry (TG). Proppant Z-23 completely satisfied the SY/T5108 -2014 standard. This study provides a new perspective for the resource utilization of water-based drill cuttings and preparation of low-density proppants.

Preparing high-strength and low-density proppants with oil-based drilling cuttings pyrolysis residues and red mud: Process optimization and sintering mechanism

This study aimed to assess the feasibility of manufacturing high-strength and low-density proppants from oil-based drilling cuttings pyrolysis residues (ODPR) and red mud (RM). The effects of ODPR and RM content on the performance of the proppants were studied, respectively. The optimum sintering condition was determined by response surface methodology (RSM), and the sintering mechanism was explored based on microstructural analysis of the proppants. The results showed that high-strength and low-density proppants with the breakage ratio of 8.6 % under 52 MPa closed pressure, bulk density of 1.45 g·cm−3, and apparent density of 2.96 g·cm−3 were obtained under the optimum preparation conditions (mass ratio of ODPR: RM: bauxite: MnO2 of 20: 8: 76: 4, sintering temperature of 1342 °C, sintering time of 1.0 h, sintering rate of 4.9 °C·min−1). The performance of the product proppants could meet the requirements of the Chinese Petroleum and Gas Industry Standard “Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations” (SY/T 5108-2014). ODPR and RM in the raw materials provided the chemical components of Al2O3, SiO2, CaO, BaO, Na2O, and K2O, which were involved in the formation of crystalline phases and molten phases during the sintering process. The performance of high-strength was primarily provided by the framework structure containing the crystalline phases and the dense structure caused by the molten phases. In addition, the Fe2O3 of RM would promote the generation of closed pores and then enhance the lightweight performance of proppants; however, excessive RM incorporation would lead to the formation of connected pores, which had a negative effect on the breakage ratio of proppants. This study not only creates a new pathway for recycling ODPR and RM within the shale gas industry but also provides a novel approach for manufacturing high-strength and low-density proppants.

Study of the influence of vibration treatment of coal cores as a way to increase gas permeability

This paper provides the results of a series of experimental studies on seismic action’s effect on the permeability of coal and hydraulic fractures. The experiments have been carried out using solid coal cores, cores with single through longitudinal cracks simulating drainage hydraulic fractures and cores with the single fractures propped with a low-density proppant designed to intensify the degassing of coal seams. The patterns of the seismic impact on the gas permeability of coal under the conditions of all-round compression have been established in accordance with the results of experiments. Also, the experimental results reveal certain patterns of increase of the drainage cracks’ gas permeability observed when the cracks are propped with proppant and are under the low intensity seismic effect under the conditions of all-round compression. The studies show that the effectiveness of seismic action increases with an increase in the accumulated exposure time, followed by stabilization and persistence of the positive effect for at least 3 - 7 days after the cessation of exposure. The obtained results provide the opportunity to assess the possibility of using seismic action to intensify the degassing of non-propped hydraulic fractures in coal mines.

Effect of proppant pumping schedule on the proppant placement for supercritical CO2 fracturing

Supercritical CO2 fracturing is a potential waterless fracturing technique which shows great merits in eliminating reservoir damage, improving shale gas recovery and storing CO2 underground. Deep insight into the proppant-transport behavior of CO2 is required to better apply this technique in the engineering field. In the present paper, we adopted a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) approach to simulate the proppant transport in a fracking fracture with multiple perforation tunnels. Previous experiments were first simulated to benchmark the CFD-EDM approach, and then various pumping schedules and injection parameters (injection location, multi-concentration injection order, multi-density injection order and injection temperature) were investigated to determine the placement characteristics of proppant. Results indicate that the swirling vortex below the injection tunnels dominates the proppant diffusion in the fracture. The velocity of fluid flow across the proppant bank surface in multi-concentration injection shows a positive correlation with the proppant concentration. Injecting high-density proppant first can promote the transportation of low-density proppant injected later in the fracture to a certain extent. Decreasing the initial injection temperature of supercritical CO2 slurry helps enhance the particle-driving effect of fluid and improve the performance of supercritical CO2 in carrying proppant.

Experimental study of seismic action influence on gas permeability of coal and hydraulic fractures

Mine field development of coal deposits is currently associated with work at depths exceeding 400m. Under these conditions the gas content of promising horizons is one of the main factors constraining the pace of development. An integral part of gas-bearing coals’ extraction is their preliminary degassing. The methane recovery ratio affects the efficiency and safety of longwall work. Degassing is intensified in order to achieve the required values of methane content in coal seams. A well-known method employed to intensify filtration processes in fluid-saturated rocks is the elastic vibrations’ treatment. The laboratory tests and field work show the positive effect of elastic vibrations on the intensification of methane desorption from coal. Modern works in this field are devoted to investigation of connections between the parameters of vibration action and the degree of increase in the methane desorption. This paper provides the results of a series of experimental studies on seismic action’s effect on the permeability of coal and hydraulic fractures. The research has been carried out on a custom designed laboratory bench. The design of the stand provides the effect of elastic vibrations of small amplitude with independent regulation of the average and differential gas pressures, axial and lateral compression of the sample. The experiments have been carried out using solid coal cores, cores with single through longitudinal cracks simulating drainage hydraulic fractures and cores with the single fractures propped with a low-density proppant designed to intensify the degassing of coal seams. The patterns of the seismic impact on the gas permeability of coal under the conditions of all-round compression have been established in accordance with the results of experiments. Also, the experimental results reveal certain patterns of increase of the drainage cracks’ gas permeability observed when the cracks are propped with proppant and are under the low intensity seismic effect under the conditions of all-round compression. The studies show that the effectiveness of seismic action increases with an increase in the accumulated exposure time, followed by stabilization and persistence of the positive effect for at least 3 - 7 days after the cessation of exposure. The obtained results provide the opportunity to assess the possibility of using seismic action to intensify the degassing of non-propped hydraulic fractures in coal mines.

How will treatment parameters impact the optimization of hydraulic fracturing process in unconventional reservoirs?

Hydraulic fracturing is a very complex process that has not yet been fully understood. Furthermore, the number of stages, length of fracture clusters in each stage, proppant and fracturing fluid compatibilities, optimum spacing length, proppant transport and placement, proppant and frac-fluid compatibility, and optimum spacing are some of the challenges inhibiting successful application of this technique across the world. In this study, we present the impact of fracture-cluster lengths, proppant types and sizes, proppant densities, frac fluid types, fluid viscosities, and injection rates on hydraulic fracturing process. Firstly, we developed a stress profile to determine initiation location and orientation of the hydraulic fractures, and subsequently created the geological layering in the zone of interest. We grouped our investigations into 5 case studies, followed by developing an efficient hydraulic fracturing design approach, and we determined the optimal treatment to achieve maximum recovery. Our results show that fracture clusters with optimal lengths will provide optimized hydraulic fracture treatment. In addition, high-strength proppants is efficient for shale formations with closure stress exceeding 5000 psi to achieve optimum fracture conductivity and fracture half-length. Furthermore, we observed the high-density proppant produced greater fracture lengths and lower dimensionless fracture conductivity (CFD), while the low-density proppant produced greater effective propped-fracture lengths and higher CFD. In some of the cases investigated, we observed that stress shadowing and interference can hinder fracture growth, eventually led to a collapse of some fractures. Our results provide valuable critical decision-making insight for optimizing hydraulic fracturing process in unconventional reservoirs across the world.

A Novel Hydraulic Fracturing Method Based on the Coupled CFD-DEM Numerical Simulation Study

For the development of tight oil reservoirs, hydraulic fracturing employing variable fluid viscosity and proppant density is essential for addressing the problems of uneven placement of proppants in fractures and low propping efficiency. However, the influence mechanisms of fracturing fluid viscosity and proppant density on proppant transport in fractures remain unclear. Based on computational fluid dynamics (CFD) and the discrete element method (DEM), a proppant transport model with fluid–particle two-phase coupling is established in this study. In addition, a novel large-scale visual fracture simulation device was developed to realize the online visual monitoring of proppant transport, and a proppant transport experiment under the condition of variable viscosity fracturing fluid and proppant density was conducted. By comparing the experimental results and the numerical simulation results, the accuracy of the proppant transport numerical model was verified. Subsequently, through a proppant transport numerical simulation, the effects of fracturing fluid viscosity and proppant density on proppant transport were analyzed. The results show that as the viscosity of the fracturing fluid increases, the length of the “no proppant zone” at the front end of the fracture increases, and proppant particles can be transported further. When alternately injecting fracturing fluids of different viscosities, the viscosity ratio of the fracturing fluids should be adjusted between 2 and 5 to form optimal proppant placement. During the process of variable proppant density fracturing, when high-density proppant was pumped after low-density proppant, proppants of different densities laid fractures evenly and vertically. Conversely, when low-density proppant was pumped after high-density proppant, the low-density proppant could be transported farther into the fracture to form a longer sandbank. Based on the abovementioned observations, a novel hydraulic fracturing method is proposed to optimize the placement of proppants in fractures by adjusting the fracturing fluid viscosity and proppant density. This method has been successfully applied to more than 10 oil wells of the Bohai Bay Basin in Eastern China, and the average daily oil production per well increased by 7.4 t, significantly improving the functioning of fracturing. The proppant settlement and transport laws of proppant in fractures during variable viscosity and density fracturing can be efficiently revealed through a visualized proppant transport experiment and numerical simulation study. The novel fracturing method proposed in this study can significantly improve the hydraulic fracturing effect in tight oil reservoirs.

Stimulation of Underground Degassing in Coal Seams by Hydraulic Fracturing Method

The problems preventing the use of mine hydraulic fracturing for stimulating the preliminary degassing in coal seams are considered. The solutions are presented for sealing the borehole interval by solidifying composition with initiator for transverse fracture of rocks. An original system for transportation of equipment along the holes and a robotized device for hydraulic fracturing of roof-and-floor selfsustaining rocks of coal seam are designed. The working fluid with a low-density proppant is proposed, which ensures creation of fractures with a high rate of methane migration.

Study on Preparation and Properties of PMMA Composite Microspheres as the Matrix of Low Density Proppant

In this paper, suspension polymerization is used for the preparation of PMMA microspheres, PMMA cross-linking DVB microspheres, PMMA-co-St composite microspheres and PMMA-St-SiO2 composite microspheres, and apply IR spectroscopy, scanning electron microscopy, compressive strength, density, thermal analysis to the prepared polymer microspheres. The purpose of our work is to find the feasibility method of synthesis process for PMMA material and composite microspheres, and the prepared theoretical basis of proppant with low density and high strength for oil drilling applications by performance test.

Influence of Compound Bonding Agent on the Performance and the Microstructure of Proppant

Low-density proppants have been developed using two kinds of bauxites containing different ratios of aluminum as main raw materials and compound liquid as a binding agent. The influences of the amount of compound bonding agent and the sintering temperature on the performance of the proppant were studied. The phase composition of calcined sample was identified by X-ray diffraction (XRD) method. The microstructure of the sintered sample was characterized by scanning electron microscope (SEM). It is shown that the proppant prepared with increasing compound bonding agent can meet the national standard. With the increase of the sintering temperature, mullite with uniform grain size is formed.

Research of Low Cost Fracturing Proppant

Petroleum has been less and less in the earth. However, only small part of the oil can be withdrawn from the oil well by the traditional method. Hydraulic fracturing is an effective way to improve the production of the oil well, in which the proppant plays an important role. As the low density proppant has the advantages of providing high flow conductivity and decreasing the consumption of the proppant, one kind of low cost and low density ceramic fracturing proppant were developed. The mechanical properties and densities of the samples were measured; then the specimens were identified by XRD and the microstructure was observed by SEM. The result showed that, when using bauxite, quartz, clay and manganese mineral as the main constituent, the ceramic proppant prepared meets the requirements of the Chinese petroleum and natural gas industry standards (SY/T 5108-2006) , in addition, it has the advantage of low cost and low density.

Techbits: Deepwater Heavy-Oil Challenge Extends to Reliable Completions

Optimized sandface and wellbore production-systems technologies intended to maximize both productivity and hydrocarbon recovery in deepwater developments were the focus of a 3-day Applied Technology Workshop (ATW) held in Brazil. Keynote speaker Ricardo Beltrao of Petrobras set the stage for the meeting by giving an overview of the challenges the energy industry is facing to produce heavy oil in deep water and by offering a glimpse of the challenges ahead. Following an agenda in which the majority of time was designated for problem solving, ATW participants heard presentations and discussion by subject matter experts, identified gaps, and then met in groups to categorize issues of concern in the following subject areas: chemicals, sand control, artificial lift, and reservoir. In the area of chemicals, discussion centered on these existing gaps for producers: - For new developments, mechanical devices are available to minimize the necessity for chemical solutions; however, such solutions are not offered on existing wells. - A process to divert scale inhibitor and remove scale in horizontal wells is needed. - A more permanent reduction of permeability to water is required. - Chemicals to prevent emulsion and organic/inorganic deposition need to be formulated. With regard to sand control, gravel packing long horizontal wells in low-fracture-gradient scenarios remains a major concern. Workshop attendees concluded that not only does the industry need to better understand fines migration in the heavy-oil environment, but it must somehow gather and connect all data from completed wells. Sand control should be approached from the standpoint of the entire operation. Of particular interest was the need to address washouts and to correctly estimate the fracture gradient. While low-density proppant plus beta and diverter valves can be used, the issue of cake removal remains. An accurate method of measuring the filter-media opening must be found to handle the mobile fraction of fines in the formation in addition to a means of measuring fines size and quantity. Is it possible to standardize comparative testing of screens, such as laser vs. sieve? A predictive technique would be extremely useful in measuring the impact of produced solids on surface equipment and filters. In an unconsolidated heavy-oil environment, taking a close look at the impact of injection above fracture pressure in gravel-packed wells is key. Currently, there exists a lack of data for injectors and for determining the appropriate method of sand control. It was emphasized that existing models for light-oil scenarios are inaccurate in predicting the potential deposition of asphaltenes and scale in the heavy-oil environment. Dialogue in the artificial-lift arena included whether electrical submersible pumps could handle gas when marginal heavy-oil fields required injection. Also, possible production of sand in flowlines represents a major problem, particularly in ultradeep water. In addition to discussion on aspects of reservoir modeling, sand prediction, and compaction prediction, water-influx and -coning control were deemed essential. Compartmentalization, in which control can be exercised over each segment, offers a solution, but while packers can isolate each single joint, they cannot eliminate water coning. The use of intelligent control devices for monitoring and control was suggested to achieve maximum efficiency.