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Abstract Laboratory tests initiated in January 1997 demonstrated clearly that periodic, large-amplitude, low-frequency strain excitation of porous media leads to large flow enhancements. Based on these results, a new liquid flow enhancement technology for reservoirs was formulated, and a successful full-scale field experiment was executed in early 1999. Other field projects in 1999 through 2001 waterfloods in heavy oil cold production wells with sand influx confirmed the expectation that pressure pulsing, properly executed, increases oil production rate at low cost. The first trial showed that periodic application of large amplitude, liquid-phase pressure pulses increased oil production rates, decreased water-oil ratio, and increased the percentage of sand produced, even without large-scale injection. Though experience to date is in heavy oil, the process is general and will work in all porous media that have interconnected pore space. Furthermore, the method works in single-phase and two-phase liquid saturated cases, although the presence of large amounts of free gas is detrimental. Based on the field and laboratory work, and considering the nature of the physical processes, it appears likely that pressure pulsing will also help reduce coning and viscous fingering instabilities, help overcome capillary blockages, and result in more total oil recovery over time. Introduction In the oil industry, progress in production technologies is most commonly based on empirical discoveries, and only later followed by attempts to develop a consistent physical theory to explain, analyse, and predict field behaviour. This is the case for all processes, such as CHOPS (Cold Heavy Oil Production with Sand), SAGD (Steam Assisted Gravity Drainage), and so on. Often, a fully rigorous physical theory remains elusive (e.g., for oil-gas-water-sand slurry flow in CHOPS production), and practice is refined through empirical models, physical reasoning and trial and error. However, the results obtained from laboratory and field research and development in pressure pulsing over the past five years were initially predicted from a new, more rigorous physical theory for porous media flow. The new theory(1) is a more complete system of equations for dynamic behaviour of interconnected multiphase porous media (matrix-liquid, including matrix-water-oil systems). It was developed by considering all relevant pore-scale physical processes (micro scale), followed by rigorous volume averaging to scale the physics up to the scale of a representative elementary volume (REV) that can statistically represent mesoscopic behaviour (cm scale). The theory is therefore consistent with the laws of thermodynamics in component phases at the pore scale, and leads to large-scale thermodynamic relationships (equations) in which porosity is found to play a fundamental thermodynamic role, similar to that of temperature in single-component systems. In other words, porosity must be treated as a basic thermodynamic variable in porous media(2). Furthermore, induced dynamic variations in porosity are responsible for the observed flow rate enhancement effect. The physical theory also dictates the experiments required to determine the parameters that arise in the equations(3). A slow dynamic wave called the porosity dilation (or porosity diffusion) wave is predicted(4).

Abstract When technology based on new science is started, there can be a lot of skepticism, which is a healthy reaction. The skepticism encountered by PE-TECH as pressure pulsing is gradually introduced has been partly overcome, but only in the Canadian heavy oil industry. Here are some typical remarks we have encountered over the last three years, accompanied by our responses. "This is not predicted by Darcy's Law." This is quite correct since Darcy's Law is a static law and cannot handle inertial effects. For example, look at how Darcy's Law is fudged to handle turbulent flow. "Well, it works in heavy oil, but it won't in light oil." Or, "Our reservoirs are different." Physics is physics; it will work in all liquid-saturated systems, but will have to be optimized in individual cases. "We don't need this because we use horizontal wells." It can be used in many different configurations, and can help horizontal wells just as it does vertical and inclined wells. "It's not the pulsing, it's a relative permeability effect (or permeability increase or viscosity decrease, etc.)." Nope, we've proven otherwise, although in the case of highly viscous oils of large molecular weight, there may be an additive effect of viscosity reduction. "It won't work in consolidated rocks." We're confident of field success; limited laboratory tests indicate that it does indeed work, but we have a lot more testing to do. "Sounds like Cold Fusion to me." Frankly, we were pretty startled ourselves at how large the effect is, but you can do the experiments yourself. "Come back when you have some real field data." We have. We're here. History Pressure pulsing is an emerging technology. Its roots go back several decades; as a rigorous theory, it goes back about 15 years. Russian engineers noticed decades ago that large earthquakes often caused changes in oil well behaviour, usually a short-term rate increase. This was variously ascribed to compaction, shaking loose of particles blocking pore throats, or changes in permeability, viscosity, and capillary entry pressure. However, attempts to use seismic excitation have, to our knowledge, met with failure in China, Canada, and the United States. Senior engineers from western oil companies have examined claims that mechanical vibrations are being used successfully, they appear unconvinced, even after site visits. Also, the numerous articles in the Russian literature, mainly by geophysicists, tend to be mathematicallyopaque, unfathomable in terms of physical processes, based on debatable premises, or without sufficient clear and unequivocal information to allow evaluation. Nevertheless, published Russian data appear convincing, and R&D programs are active in Alberta, USA, and other areas, albeit without much apparent success. We believe we know why: seismic excitation is the wrong type of impulse, of insufficient amplitude, and applied at the wrong place. Pressure pulsing experiments in the laboratory started only in January 1997; in the field, it was first tried in June 1998. PETECH conducted the first commercial applications in workover mode in September 1998, and in full field-wide rate enhancement mode in June 1999.

Abstract The Buckley-Leverett theory is discussed in light of the recently proposed flow equations involving "generalized relative permeabilities". In particular it is argued that because capillary pressure was ignored in the Buckley-Leverett analysis, internal consistency requires that the parameters be corrected for the removal of interfacial tension. The results indicate a tendency toward removing the inflection point all the fractional flow curve, which is the mathematical source of an unphysical saturation profile. Introduction Any attempt to describe the flow of multiple phases through a porous medium must address the complex problem of incorporating interfacial phenomena from the pore scale into a larger-scale description of the dynamics. In particular, for water-oil displacements, motions of the fluid-fluid interfaces, the formation of oil ganglia and the wetting characteristics of the medium introduces "capillarity" into the dynamics. The importance of these processes in oil recovery mechanisms has been the subject of a great deal of research (e.g. Melrose and Brandner, 1974; Stegemeier, 1977; Mohanty et al., 1980; Takamura and Chow, 1983). However, difficulties in incorporating this information into larger-scale descriptions of the flow dynamics have been a stumbling block in attempts to describe the dynamics of multiphase flow. Furthermore, pore size distribution and pore geometry have been shown to have a large effect on the trapping of oil ganglia (cf. Chatzis et al. 1983, Wardlaw, 1982) and thus residual oil saturations. The description of multiphase flow which has been generally accepted is based on an analogy with single-phase flow. Proposed by Muskat (1946, 1953) over thirty years ago, it assumes that multiphase flow can be adequately described by flow equations of the same form as Darcy's equation. Permeability is replaced by parameters called relative permeabilities which are taken as functions of fluid saturation. Thus all the dynamic interfacial phenomena which occur at the pore scale during multiphase flow are to be handled by this single modified term in each of the flow equations. A more rigorous understanding of the dynamics of multiphase flow, in terms of pore scale phenomena, could not be considered at that stage since Darcy's equation itself was only understood as an empirical relationship. A number of researchers subsequently speculated that Darcy's equation was illustrating the average behaviour of the well understood flow dynamics at the pore scale (i.e. the Navier-Stokes equation) and the effects of the complex boundary between the fluid and the solid medium (e.g. Hubbard, 1956; Hall, 1956; Scheidegger. 1974). The main obstacle in these analyses to a clear formulation of the problem, was how to relate the averaged effect of the differential equations at the pore scale to the Darcy description which expressed the problem as a differential equation of the averaged quantities. A breakthrough came when Whittaker (1969) and Slattery (1969) proved what has come to be known as the Whittaker-Slattery averaging theorem. This mathematical result expresses the volume average of the spatial derivative of a microscopic quantity in terms of the derivative of the volume averaged quantity plus a surface integral over the interfaces between the fluid and solid.