The goal of this project is to develop an “engineered ice” or “rusting rebar” proppant that can deliver large localized forces to fracture rock under high constraining forces, similar to how water freezing or rebar rusting cause fracture in rock and concrete structures. The overall objective of this project is to develop a new class of structural expandable proppant particles that can deliver a pumpable formulation that is capable of exerting considerable force to open and extend fracture networks for oil and gas, mineral, and geothermal energy extraction from deep hardrock and tight formations.
Terves, Inc., Euclid, OH 44117
The exploitation and recovery of gas from hydraulically-fractured unconventional formations, such as shale, are changing the United States (U.S.) from a net energy importer to a potential exporter. According to the U.S. Energy Information Administration, Office of Energy Analysis, over 33 million barrels of oil and 1,480 trillion cubic feet of natural gas are technically recoverable from shale and tight formations in the U.S. Currently, oil recovery rates are less than 7% on average, while gas recovery rates remain around 25% of total recoverable reserves. Furthermore, current hydraulic stimulation processes utilize large amounts of water, which must be treated and disposed of during flowback.
This Phase I & Phase II SBIR continues to develop an engineered stimulation fluid alternative that can provide the controlled application of force independent of flowrate to widen and extend fracture networks, and to prevent fine fracture closure after removal of pumping pressure. This expandable proppant is expected to have the ability to stimulate the reservoir with higher degrees of control and reduced water usage, and to address fine fractures that are currently unable to be efficiently propped. These “engineered response” proppants are an initial application of engineered pumpable materials - other applications include local chemical delivery, tracer release, and thermal energy delivery. Key technologies being leveraged and further developed for expandable proppant development include; controlled release coatings for proppants (to control exposure to the formation fluids), reactive nanoparticle fabrication and dispersion, scalable nanocomposite bead production, proppant transport CFD simulation, and proppant conductivity advanced test methods.
The project team will characterize the underlying kinetics and effectiveness of the expandable proppant chemistries and determine the engineering basis for their use, using both experimentation and simulation tools. Methods for controlling the amount of force delivered, and the placement and timing of the force delivery, as well as long term stability (creep, dissolution, etc.) will be developed leading to use protocols for different formation types. The function and resultant fracture conductivity after stimulation and formation closure during fluid removal will be measured using API reference methods as a function of formation type (carbonate, shale, sandstone), as well as placement methodology (i.e., pillar, less than monolayer, multilayer).
Using expandable proppants, increased fracture conductivity is expected through the delivery of smaller, lighter proppant particles that swell after placement to overcome embedment and fracture closure stresses to open, extend, and maintain complex fracture networks beyond the near-bore area. Lighter and smaller proppants can be delivered with lower fluid pumping rates and viscosities, and expandable proppants can subsequently deliver forces exceeding the 2500 psig demonstrated during Phase I while retaining high permeability. The expandable proppants can be pumped into a fracture network and then, in a controlled manner based on changes in temperature, time, or formation chemistry, can deliver additional force that opens and extends the crack network, in a manner similar to steel rebar rusting and fracturing concrete.
The capability to have a pumpable material that can be triggered to provide the controlled application of high forces while remaining highly permeable is a potentially enabling fracture technology for resource extraction. When applied to oil and gas stimulation operations, the ability to expand existing fracture networks without the use of large volumes of water or other fluids can greatly reduce costs and environmental impacts. The proposed controlled application of force through in-situ reaction with formation fluids after placement will provide a new tool for reservoir engineers to utilize in enhancing the economics of extracting natural resources. The practical and cost-effective ability of controlled application of localized force offers a new engineering tool to control the development of fracture networks, including guiding the direction, extent, width, and longevity of the fractures, and can be used to control residual stresses in formations.
Terves is still working with Idaho National Laboratories in developing their DEA fracture and proppant model to address soft-rock and plastic proppant performances. Their time to dedicate towards development and modeling is limited and has been stretched, but are working with a revised model now and plan to have four sets of data on proppant crush and embedment in hard and soft-rock fractures, using a single partial mono-layer pack design of Terves’ expandable plastic proppant and standard hard sand proppant.
Terves’ work initially took on adapting the current API 19 (ISO 13503-5) standard to address partial mono-layer packing (~0.02lb/ft2 for sand proppant) in carbonate core rock slabs for the fracture. Repeating test failures occurred with leaking, so Terves has been in the process of developing the method to address the issues of fracture conductivity measurements with partial mono-layer packs and soft rock samples. Developed and notable items learned include:
A recent test has been successful and current testing is going forward to complete the initial test matrix of testing hard proppants and plastic expandable proppants within the softer carbonate rock samples. The experimental test results will be used in validating and making necessary adjustments to the equivalent modeling system. Again, the theory is plastic expandable proppants have the propping performance needed to maintain far-field fractures in the soft carbonate shale plays where hard sand and ceramic proppants just embed at the partial mono-layer packing.