ENHANCED RECOVERY UNITS AND PRESSURE MAINTENANCE
| Jurisdiction | United States |
(Jan 1990)
ENHANCED RECOVERY UNITS AND PRESSURE MAINTENANCE
Brown & Drew
Casper, Wyoming
I. INTRODUCTION, DEFINITIONS AND CAVEATS.
The terms "enhanced recovery" and "pressure maintenance" apparently have differing meanings or, at least, more or less inclusive definitions depending upon whether one is discussing the terms with attorneys or technical personnel involved in the oil and gas industry. Moreover, there appears to be either confusion between or some overlapping of the terms "enhanced recovery" and "secondary recovery".
For example, a court, in generally discussing several of the terms has recently opined as follows:
In order to understand the nature of this appeal it is helpful to be cognizant that when oil is initially discovered, it flows or is pumped to the surface via wells, assisted by natural pressure existing in the subsurface. This process is termed 'primary' recovery of oil. As the natural pressure dissipates, oil production declines. Production can sometimes be restored by injecting water (termed 'secondary' recovery) or other substances...(termed 'tertiary or enhanced' recovery) through wells to restore or increase pressure. This restoration is expensive and often times can only be made cost effective if various owners of tracts of land consolidate their resources in
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order to maximize their return of oil. This consolidation occurs via what is termed unitization.
In the matter of Koch Exploration Company, 387 N.W.2d 530 (S.D. 1986).
Similarly, a recognized expert in the field, Dr. H. K. van Poollen, in Fundamentals of Enhanced Oil Recovery, does not address waterflooding of oil reservoirs, understood by this author to be the most common form of "secondary" recovery, but rather discusses more exotic recovery processes involving, for example, steam stimulation, in situ combustion, surfactant polymer injection, polymer flooding, caustic flooding, miscible hydrocarbon displacement, carbon dioxide injection, and inert gas injection. (H. K. van Poollen and Associates, Inc., Fundamentals of Enhanced Oil Recovery, PenWell Books, 1980.) However, the Interstate Oil Compact Commission in its publication, Improved Oil Recovery, discusses not only the more exotic forms of hydrocarbon recovery, discussed by Dr. van Poollen, but also waterflooding and "improved waterflooding". (Improved Oil Recovery, Interstate Oil Compact Commission (1983).)
Williams and Meyers in their Manual of Oil and Gas Terms, define "enhanced recovery", on the basis of an Alberta, Canada, oil and gas conservation enactment, as follows:
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[T]he increased recovery from a pool achieved by artificial means or by the application of energy extrinsic to the pool, which artificial means or application includes pressuring, cycling, pressure maintenance or injection to the pool of a substance or form of energy but does not include the injection in a well of a substance or form of energy for the sole purpose of (i) aiding in the lifting of fluids in the well, or (ii) stimulation of the reservoir at or near the well by mechanical, chemical, thermal or explosive means.
Williams and Meyers, Manual of Oil and Gas Terms "Enhanced Recovery".
Williams and Meyers define "secondary recovery" as follows:
Broadly defined, this term includes all methods of oil extraction in which energy sources extrinsic to the reservoir are utilized in the extraction. One of the early methods was the application of vacuum to the well, thus 'sucking' more oil from the reservoir. The term is usually defined somewhat more narrowly as a method of recovery of hydrocarbons in which part of the energy employed to move the hydrocarbons through the reservoir is applied from extraneous sources by the injection of liquids or gases into the reservoir. Typically, a differentiation is made between secondary recovery and pressure maintenance; the former involves an application of fluid injection when a reservoir is approaching or has reached the exhaustion of natural energy, while
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the latter involves an application of fluid injection early in the productive life of a reservoir when there has been little or no loss of natural reservoir energy. ***
The term 'secondary recovery' has been defined by a subcommittee of the American Petroleum Institute as 'the oil, gas, or oil and gas recovered by any method (artificial flowing or pumping) that may be employed to produce them through the joint use of two or more wellbores. Secondary recovery is generally recognized as being that recovery which may be obtained by the injection of liquids or gases into the reservoir for purposes of augmenting reservoir energy; usually, but not necessarily, this is done after the primary-recovery phase has passed.' [Citation omitted.]
Williams and Meyers, Manual of Oil and Gas Terms "Secondary Recovery" (emphasis supplied).
Further, Williams and Meyers have defined "pressure maintenance" as follows:
The injection of gas, water or other fluids into oil or gas reservoirs to maintain pressure or retard pressure decline in the reservoir for the purpose of increasing the recovery of oil or other hydrocarbons therefrom. [Citations omitted.]
Williams and Meyers, Manual of Oil and Gas Terms "Pressure Maintenance".
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For purposes of the discussion which follows, "enhanced recovery" will be utilized as a generic term including any and all projects by which artificial energy or substances not naturally occurring in the hydrocarbon reservoir are introduced in a wellbore or wellbores, and the production of hydrocarbons, having been thereby facilitated, being accomplished through other wellbores. Broadly defined, the term would include typical waterflood projects, and any and all of the more exotic forms of improved recovery techniques, including pressure maintenance operations. However, given the relatively more special circumstances under which pressure maintenance projects are undertaken and facilitated, pressure maintenance projects will be considered as a special matter.
In sum, given the elasticity in the term "enhanced recovery", the author will utilize this term as one including both more traditional secondary recovery projects, and the more exotic techniques having been developed in recent times, excluding, however, "pressure maintenance" projects. Pressure maintenance activities will be considered separately since they are, in the author's understanding, undertaken at a different time in a given hydrocarbon reservoir's life, and can and do, in the author's experience, involve special and separate consideration.
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By way of caveat, what follows is not intended to be a survey of the compulsory unitization laws of all of the Rocky Mountain States. (See, Romanov, "Statutory Unitization: Significant Legal Issues" 12 Oil and Gas Conservation Law and Practice, Paper 12 (Rocky Mountain Min. L. F. 1985)). Rather, the author intends to attempt to cover the topic assigned by reference to several existing units in the State of Wyoming and the Wyoming oil and gas conservation law as exemplars. Accordingly, practitioners from jurisdictions other than Wyoming and other parties interested in jurisdictions other than Wyoming are advised to fully examine the individual jurisdiction's compulsory unitization law and other matters of local concern.
II. ANALYTICAL FRAMEWORK AND DISCUSSION.
As noted by one of the other authors and speakers at this Special Institute, while there are suggested guidelines by the Bureau of Land Management, Branch of Fluid Minerals, concerning "secondary recovery" units, and, in fact, a federal form of unit agreement for "secondary recovery" projects, neither the agreement itself, nor the suggested guidelines, are apparently in the form...
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