Pressure Pulsing at the Reservoir Scale: A New IOR Approach

Abstract

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).