The goal of a hydraulic fracturing treatment is to create a high permeability pathway to limit how far the reservoir fluids have to move through the matrix.
Micro-proppant pack permeability can become close to the permeability of the matrix.
Silica micro-proppants, and angular ceramic micro-proppants have reduced permeability and crush strength, if the permeability of these proppants is the same, or is close to the permeability of the matrix, operators are wasting capital.
DEEPROP® provides a high degree of permeability relative to the rock matrix into operators micro-fracture network, and keeps these fractures propped open due to its high crush strength..
The apertures of hydraulic fracture swarms and complex fracture systems are likely too narrow for proppants that are 100 mesh or larger to enter. Micro-proppants can enter fractures that are 10 times smaller than 100 mesh, and the settling velocity of micro-proppant is 35 times slower than 100 mesh. Micro-proppant expands operators ability to place proppant inside smaller more complex fracture systems, and incrementally increase the propped fracture area in unconventional shale plays.
The purpose of hydraulically fracturing unconventional shale plays is not just to contact as much reservoir surface area as possible, it is also to efficiently drain as much reservoir as possible. The issue with current proppant technology, like 100 mesh proppants or larger, is that they are to big to enter the tiny pre-existing fractures and faults, and too big to enter the hundreds of propagating hydraulic fractures that are being created; micro-proppants can enter fractures that are 5-10x smaller than 100 mesh, or about the width of a human hair (100µm). But proppants that are this small, have a very tiny proppant pack permeability, simply due to their small size. In fact, the permeability of a micro-proppant pack can be the same order of magnitude as the matrix permeability in the formation. It is critical for operators to select a micro-proppant that provides enough permeability to transmit the fluids through the narrow micro-fracture network efficiently, if they don’t, they will be wasting capital.
The purpose of hydraulically fracturing the rock is to create a more efficient flow path for the reservoir fluids to move from the matrix to the wellbore. The reason is because, for example, it takes 3-years for methane to diffuse 3-10 meters in 10-100 nano Darcy rock, and it takes oil 3-years to move 1-2 meters in the same rock. The shorter the distance the produced fluids must travel through the low permeability matrix, to a high permeability pathway, and keeping these pathways open for as long as possible; is beneficial for an operator’s production.
Figure 1: The time required for methane to diffuse through typical matrix permeabilities is given on a linear scale on the left and a log-log scale on the right. The gray region indicates that approximately three years are required for gas to diffuse approximately 3-10 m through 10-100 nanodarcy matrix to a high permeability pathway. The corresponding time/distance relationship for oil is shown in red, with an approximately factor of 10 higher viscosity resulting in a corresponding decrease in diffusion distances. The gray and pink boxes reflect a representative range of matrix permeabilities for unconventional reservoirs. From Hakso & Zoback (2019), taken from Zoback and Kohli (2021).
Using micro-proppants to enter tiny fractures allows operators to prop more reservoir surface area and prevent those tiny fractures from closing over time. In the past, operators have tried using silica micro-proppants but the permeability of silica micro-proppants is so low that it doesn’t provide any benefit; DEEPROP® is a ceramic micro-proppant technology. There are several differences between silica and ceramic micro-proppants that I believe are what makes DEEPROP® successful; they are differences in crush resistance and permeability/conductivity.
It seems counterintuitive that proppant conductivity could play a role in unconventional, low-permeability shale plays. But I want you to consider the size of the particles of a micro-proppant, the width of the fractures that a micro-proppant can enter, and the permeability of the micro-proppant pack relative to the permeability of the rock matrix that is being stimulated. I’ll demonstrate this using conductivity data for DEEPROP®1000. Conductivity testing was carried out by C&A Labs, and the results are shown below.
Figure 2: Conductivity testing data conducted by C&A labs on DEEPROP®1000. The conductivity data indicates that DEEPROP®1000 can provide a high permeability pathway for reservoir fluids in formations with matrix permeability less than 5µD.
Using the conductivity data above, If I assume a minimum fracture width of 0.21mm (a 3x bridging factor for DEEPROP®1000), the minimum permeability of a DEEPROP®1000 proppant pack ranges from 0.138 µD to 0.413 µD, or 138 nD to 413 nD at effective stresses of between 10,000 psi to 2,000 psi. The permeability of the proppant pack is perhaps an order or two in magnitude above the matrix permeability for a typical shale formation – The Key Takeaway is that the Permeability of a Micro-Proppant Pack is Tiny.
I have requested conductivity data from 5 silica micro-proppant and one ceramic micro-proppant supplier, none have been willing to share conductivity or crush data, which is telling by itself, but if we assume it is an order of magnitude less than DEEPROP® – not a crazy assumption; then silica micro-proppant permeability would be on the same order of magnitude as the matrix permeability. This would not be surprising, given that the average diameter of the clastic grains in a shale matrix are 50µm, which is about the diameter of 200-300 mesh silica flour and fumed silica. This would explain the lack of incremental production when using silica micro-proppants; the permeability of the silica micro-proppant pack is the same as the matrix permeability. For a micro-proppant, conductivity matters because the proppant pack permeability becomes close to the permeability of the shale matrix. If the micro-proppant selected does not have a high permeability relative to the shale matrix, it will not provide any production upside – it is like re-filling the micro-fractures you created with matrix material.
I also believe that crush strength play an important role, both in keeping the micro-fractures open and for maintaining conductivity/permeability within the micro-fracture network. As mentioned above, no supplier that I have contacted has been willing to provide crush data for their silica micro-proppant, the same can be said of the competitive ceramic product, again, this is telling. Given the angular, jagged shape of silica flour and fumed silica micro-proppants (shown below), I believe the crush strength is low, this probably explains why no one is willing to supply the data. A low crush strength would cause spalling, and fragmentation of the proppant grains, further reducing the already low permeability values, and allow the micro-fractures to begin to close.
Figure 3: Silica flour and fumed silica, it’s clear how the grains would stack together like lego bricks, and that there are many contact points for grains to crush, spall, and fragment to reduce the proppant pack permeability even further.
One final theory for what makes DEEPROP® work so well at providing incremental production is the erosion of near wellbore tortuosity. As the fracture initiates, and re-orients as it propagates away from the wellbore, there is often a near wellbore constriction that the fluid must pass through. This constriction can cause significant friction pressure during the hydraulic fracturing treatment, and acts as a choke during production, causing pressure loss in the reservoir. What has been observed during treatments with DEEPROP®, are pressure drops of between 800-1,200 psi as soon as DEEPROP® hits the perforations. What we believe is that the Bernoulli effect causes DEEPROP® to be concentrated in the centre of the fluid stream, as DEEPROP® is a very hard and durable material, it abrades this near wellbore constriction. This reduces the near wellbore convergent effects and limits the reservoir damage during production.
At proppant diameters of 100 mesh or larger, the permeability ratio of the proppant pack to the matrix is so high it does not matter what kind of proppant operators choose; silica, or ceramic. But when you begin to consider the permeability of proppants that are 200 – 300 mesh, or 400 – 500 mesh, like DEEPROP®, the permeability of the proppant pack becomes critical, and it is something that needs to be carefully considered. Pumping a micro-proppant that has the same permeability as the rock fabric is not going to be beneficial for operators, in fact, it will be a waste of capital. As Carl Montgomery often says - when you pump a frac, what you are paying for is conductivity. DEEPROP® has been successful because it is small enough to enter micro-fractures and delivers a high permeability to the micro-fracture network, relative to the rock matrix, in spite its tiny size.
Figure 4: Microscopic image of DEEPROP®1000 placed on a core sample prior to conductivity testing. DEEPROP® is perfectly spherical, the best shape for retaining conductivity and providing a high crush resistance.
Next week I will start to dive into the field trials and the results that operators have achieved using DEEPROP®!
If you would like to learn more about how DEEPROP® can enhance your proppant placement and provide incremental production, please get in touch with me or send an email to email@example.com
We’re also hosting a booth at URTeC, booth 4600 from July 26-28th! I would encourage you to stop by for a chat, we would love to meet you.