Reservoir Mechanics - Stylized Myth or Potential Science?
Authors: Wyllie M.R.J. 
Published: December 2007

The Nature and Task of Reservoir Mechanics

What is reservoir mechanics, or as some less research-minded people might prefer to put it, reservoir engineering? Is it, in the du Pont-inspired words of one of our local radio announcers, a foundation for "better things for better living through chicanery", or is it something which we can in good faith describe as a science? Is it an elaborate myth, or is it the fundamental tool which can offset the present inexorable climb in the costs of finding oil in the United States? Let me say that I believe the latter statement to be the true one. while the reservoir mechanics profession is presently respectable, I must point out that there is danger of its falling into disrepute unless attempts are made to curb present extravagances and to disseminate more widely knowledge concerning its inherent strengths and basic weaknesses. The mood of the oil industry today is not one of expansion or, at least, not of expansion of personnel, either technical or otherwise. Many companies are carrying on their production activities with a staff which is less than one-half the size of that which existed less than five years ago. Staff reduction has not necessarily reached its nadir. It is imperative, therefore, that the reduction in the quantity of engineering talent be more than offset by an increase in quality and, in particular, by an increase in productivity. A productivity increase can be effected in two ways. The first is by clear thinking, the second by automation. Both are vital, but for the sake of brevity I shall not here consider the latter. Let us go back to fundamentals. What is the essential job of the reservoir mechanic? Surely it is to get more oil out of the hydrocarbon accumulations which have been so laboriously (and, happily, inexpensively) found in years past. Even allowing for the mystique on which I shall comment later, it appears that (tar sands and oil shales excluded) there may well be in excess of 100-billion bbl of oil which are known to exist in this country but which are presently deemed economically unrecoverable. This 100-billion bbl means something like $300 billion. Even if allowance is made for the conservative view of J. Paul Getty that a billion dollars is not worth what it used to be, this is a tempting target. Certainly it is a target which should be aimed at if, as some figures show, it now costs more than $3.00 to find a new barrel of producible oil. The recovery of that 100 billion bbl is not going to be easy. But its recovery will be made more difficult if those who control the means to conduct research and the resources to pioneer novel field techniques do not reject specious and ill-defined processes, and avoid being misled by the euphoric misanalysis of pilot studies. If true progress is to be made, it is particularly essential that only the most dispassionate appraisal be made of pilot projects. Too many pilots are only successful because of judicious interpretation; technically, they are failures. It is a sad commentary on the degree of governmental control in our economy that suppressio veri or suggestio falsi when applied to field trials can sometimes be remunerative. I believe that because of political considerations many novel schemes for increasing recovery are taken to the field at a date far earlier than can be justified technically. Such trials may be not only technical travesties but ones that, by their very nature, may ultimately undermine those who strive for true technical progress. The danger of a technically unsound trial lies in the cynicism engendered by the too-frequent crying of "Wolf!". Eventually, those who have new schemes for oil recovery which are properly understood and have been adequately tested in the laboratory will be impeded.

Surface and the Problem of Oil Recovery

The problem of total oil recovery is not merely one of having enough reservoir energy available; it is primarily the problem of directing that energy. Essentially, the recovery of oil involves the ability to overcome surface forces. In homely terms, the average oil reservoir contains about 1/2 gal of oil/ acre of rock surface. Consider that amount of oil spread on a fair-sized parking lot. It might then be considered pretty smart to recover one-half of it if what is recovered only commands $ .07/gal (equal, in fact, to the usual state tax on 1 gal of gasoline). Regrettably, of course, it is not smart enough by a factor of about two. More scientifically put, many petroleum-bearing rocks have an envelope surface area of about 500 sq cm/cc of pore volume and a surface area (if measured by the B.E.T. or gas-adsorption technique) of about 0.5 to 1.0 sq m/gm.

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