DF2S Technology

Summary

HLM energy is developing the DF2S Radio Frequency (RF) stimulation process/system which will allow access to the oil potential in the vast oil shale resources in the US and around the world. This process/system can also be used as a post processing technique for hydraulically fractured shale oil plays.

     This innovative process/system uses RF electromagnetic (EM) energy to accomplish two tasks at once. These are (1) kerogen maturation to produce additional hydrocarbons (pyrolysis) and (2) enhancing matrix permeability. Innovations include: 

  • An in-situ RF based heating process that will produce the desired EM fields where others have failed.
  • The ability thereby to enhance matrix permeability of a controllable volume surrounding development wells, leading to recovery rates between 60% and 80%
  • The potential to increase HC in place by in situ pyrolysis.
  • The ability to design a modified well geometry to exploit these innovations. 
  • A controlled and bounded increased permeability volume. This is different from fracking, where it is common knowledge that a new well can in some cases kill an old well at distances exceeding several kilometers. For RF cracking there is little interference between wells because the cracked volume is well controlled. 

     The net effect of these innovations will be to produce a multi-year oil and gas “factory” which will provide continuous production for twenty years rather than the typical recovery spike followed by an exponentially decreasing tail. 

     As noted above, RF heating will convert thermally immature kerogen to oil and gas through pyrolysis. This allows access to the vast oil potential of U.S. oil shale. In a DOE report from 2006 it was stated that there are 1.2 trillion barrels of potential oil in kerogen deposits of greater than 25 gal/ton. The system has been predicted to yield internal rates of return between 20% and 50% for these deposits. This will increase US oil and gas reserves by an order of magnitude.


In situ Pyrolysis:

     RF heating is not new. However, the problem with previous RF designs was the field structure around the RF probes. Almost all those systems used antennas, and antennas do not work as expected underground. This system uses an alternate RF application system which overcomes the problems seen with previous RF based systems.

     As noted above, RF heating will convert thermally immature kerogen to oil and gas through pyrolysis. This allows access to the vast oil potential of U.S. oil shale. In a DOE report from 2006 it was stated that there are 1.2 trillion barrels of potential oil in kerogen deposits of greater than 25 gal/ton. The system has been predicted to yield internal rates of return between 20% and 50% for these deposits. This will increase US oil and gas reserves by an order of magnitude.

     This system can also be used as a post processing technique for fracked shale oil fields. The recovery percentage will be an order of magnitude higher than that obtainable by traditional fracking. Further, if thermally immature kerogen is present in these tight shale oil fields, the kerogen will be converted to oil and gas and recovered as well.  

     Because so little of the hydrocarbons in place are removed by fracking, the system will barely notice that the fields have already been fracked. Old fracked tight shale oil fields become a valuable asset. The extent of the economic viability of this will be determined by the amount of thermally immature kerogen in place that can be converted to oil and gas in the process. 


Matrix Permeability:

     Instead of using hydraulic fracturing to create or enhance a network of permeable fractures to drain a low-permeability matrix volume, RF heating is used to cause fracturing of the matrix itself to enhance its permeability. The volume of rock fractured will likely be smaller than the volume within which the hydraulic fracture network is contained (often referred to as a Stimulated Rock Volume or SRV), but the permeability increase will occur in a more homogeneous fashion (i.e. it won’t just increase along existing bedding planes and joints). Further, testing has shown that process in situ conversion also causes a marked increase in permeability from the nano darcy level up to the 100s of millidarcy level

     Understanding the production of a fracture system which uniformly increases the permeability of the rock is critical for this system/process. Competing technologies for increasing permeability (hydrofracturing using water or other fluids) produce discrete systems of fractures without affecting the intrinsic permeability of the surrounding matrix. Production is restricted to within a few meters of the created fracture systems, which are often inherently sparse and/or constrained to follow by pre-existing discontinuities. Fracture lengths are difficult to predict or control, leading to large risks and uncertainties associated with lack of knowledge of where the produced fractures have propagated. 

     Given the right conditions, RF heating can introduce distributed fractures at all scales within a controllable and known volume, increasing intrinsic matrix permeability and enabling very high recovery rates of hydrocarbons in place. One of the potential ancillary benefits of in situ heating is that the system will dewater clays and other ductile minerals that cause rapid decreases in fracture conductivity both through the process of proppant embedment of propped fractures and through creep closure of rough fracture walls whose misalignment during the stimulation process produces temporary enhanced conductivity. This too will help to reduce production decline by maintaining system permeability. 

     Unlike fracking, where it is common knowledge that a new well can in some cases kill an old well at distances exceeding several kilometers, for RF cracking there is little interference between wells because the cracked volume is well controlled. 

     Evidence that heating can significantly increase in situ permeability of shales comes from a research, development, and demonstration program to determine the feasibility of developing the vast US oil shale deposits initiated by the US Bureau of Land Management (BLM) [REF 2]. Both AMSO and Shell participated and based their systems on increased permeability due to heating. AMSO claimed the potential to develop high permeability fracture fields extending out 100 ft from the well bore. Shell demonstrated 60% recovery for oil during their pilot due to increased permeability caused by heating and cracking.

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Process 

An example model for how an RF heating system might be deployed to enhance production is as follows. The process would employ a downhole, 3-dimensional electromagnetic energy array to precisely deliver heat to a sequence of large shale modules. In the example above, these are 100,000 ton, 50,000 cubic yard shale blocks. A set of horizontal wells is drilled in a regular cross-sectional pattern. Each horizontal leg is 5000 feet and finished with a number of individually activated RF segments. In this example, that is one system. After the majority of oil and gas has been removed from the first block, the next section of the array is energized, and the process starts over. See Figure above. The figure shows the blocks for a set of 9 systems laid out in a three by three square. For the system described, this process can be repeated yearly for almost 20 years. The result is a constant yearly flow of oil and gas, with no “exponential” decline as is normally seen in wells where hydraulic fracturing is employed. This radically alters the economics of unconventional oil and gas recovery. It looks more like an oil and gas factory with continuous output rather than a typical well system. 

     All of this is accomplished by deployment of RF heaters in wells drilled using existing technology. While the number of wells is larger than is typical for fracked wells, expected recovery will be more than an order of magnitude greater than with hydraulic fracturing for multiple reasons. The process enhances matrix permeability allowing a much larger portion of the natural resources present to be retrieved than in hydraulic fracturing, where a nano-Darcy permeability matrix is drained through a sparse network of fractures. Couple this with the decreased risk of fracturing out of zone, or of well interference of closely spaced fracked wells. Finally add in the potential of additional hydrocarbons produced through in situ pyrolysis and the amount of resources recovered per volume will be much larger than conventional fracking. 


Risks: 

     This RF heating process is in the advanced development phase. Initial modeling, done in a sequential fashion without feedback between the models, has shown that this process will likely be successful in shales with high kerogen content, such as the Green River formation or portions of the Bakken. Retorting is a well understood process. Our process provides a cost-effective way to do retorting in situ. Due to the high stresses and cracking generated, known permeability increases from in situ conversion, increased recovery is a foregone conclusion. 

  1. The electrical characteristics of the system and the environment will vary with temperature. A matching system/process must be designed that can be implemented in a restricted space at a reasonable cost. The requirements for this system will only be known once the modeling provides a prediction of those changes which includes coupled effects. 
  2. As shale is heated by this RF process, many parameters change. The feedback between the various processes needs to be included in the model to produce an understanding of how well the proposed process will work. 

All the above risks are being retired through our NSF financed R&D work.