The properties of limestone reservoir rocks such as the distribution anddegree of continuity of the pore systems, and the relative volumes andpermeabilities of the systems making up the complex cause large variationsbetween performance of individual limestone reservoirs and their susceptibilityto secondary recovery methods. The effects of these factors on the mechanism offluid flow cannot be adequately evaluated with presently developed concepts, laboratory data, and geological information. The observance and interpretationof the performance of individual limestone reservoirs provides, at present, themost adequate approach for evaluating the integrated effects upon performanceof the many, now immeasurable variations in the properties of limestonereservoirs. Introduction The development and application of techniques for increasing the efficiencyof oil recovery from natural reservoirs is a problem of primary importance tothe industry. During the past several years, a great deal of effort has beenexpended by the technical personnel of the industry toward the improvement ofpresent known methods of oil recovery, and evaluating the factors which controlthe susceptibility of particular reservoir types to economic application ofsecondary recovery methods. Providing adequate and accurate laboratory data onthe properties of the reservoir rock and its contained fluids, together withgood production statistics, are available, methods have been evolved forestimating with reasonable accuracy the performance of an oil reservoir undereither continued natural depletion or conditions imposed by introducingadditional displacing fluid into the reservoir from an extraneous sourcethrough the injection of gas and/or water. The susceptibility of limestone reservoirs to secondary recovery by gasinjection is very much dependent upon gas-oil relative permeabilityrelationships for the reservoir in question. In a rock formation in which theporosity is of the intergranular type such as is found in sand stones and somenonfractured dolomites, a representative sample of the pore structure can beobtained in a small core plug. In this type of reservoir, it has been shownthat relative permeability data obtained from laboratory experiments can beproperly applied to evaluate the flow relationships actually observed duringthe depletion of a reservoir. In addition, a good idea of the fraction of thereservoir which will be swept by the injected gas may be obtained from thespacing pattern used and the permeability profile of cored wells. From thesedata, it has been demonstrated that reliable estimates of performance andrecoveries under gas injection operations can be made for reservoirs in whichthe porosity is of the intergranular type. T.P. 2638
The various theories as to the well spacing-recovery relationship are reviewedin considerable detail and these theories analyzed in terms of theirconsistency with modern reservoir engineering concepts. It is concluded thatthe well spacing problem must be analyzed in terms of recovery efficiency andthat a positive answer to the relation between well density and recoveryefficiency is not available from direct comparisons of the production historiesof wells and fields. The results of an engineering analysis designed to permit approximatecalculation of recovery efficiencies as a function of well spacing in adepletion type reservoir from basic reservoir data is presented. Results ofthis type analysis indicate that the effect of well spacing on recoveryefficiency in depletion type reservoirs can be expected to be very small.Limitations of this approach are pointed out, particularly with respect to itsapplication in lenticular reservoirs. Testing techniques are outlined which should indicate whether or not areservoir is continuous between wells and whether or not satisfactory drainageis being obtained with present spacings. A mass of data of this type indicatescontinuity to exist in most fields. Introduction The purpose of this paper is to review critically the engineering aspects ofthe well spacing problem, both from the standpoint of certain concepts and fromthe standpoint of reservoir mechanics. The well spacing problem is primarily aneconomic problem in which the optimum well density for a particular field isthat density which will yield the greatest oil recovery consistent withjustifiable development costs. The well spacing answer in terms of economicconditions, however, is extremely sensitive to the variation in recoveryefficiency with well density. The variation in recovery efficiency with welldensity is properly an engineering problem. Different opinions as to thecorrect answer to this engineering problem is the basis for most of the widedifference in opinion among various members of the industry as to optimum wellspacing. This paper will be confined to the engineering problem of the relationbetween well density and ultimate oil recovery; economic considerationsnecessary for the evaluation of optimum well density for any particular fieldwill not be discussed. T.P. 2938
With the emergence of Petri nets in practical applications the need to reverse-engineer them arises. Folding based reverse-engineering techniques are crucial for Petri nets. But after a translation step they offer novel analysis capabilities for other systems. Such a translation makes Petri nets a powerful and intuitive engineering metaphor outside their traditional strength for concurrency.We present a folding-based algorithm which transforms an unstructured flat net into a coloured net. In reverse engineering terms, it recovers a high-level design, a structured specification and a data model from an existing system. Both the algorithm and the translation to Petri nets allow many variations for adaptation to different tasks. Moreover, the cost is almost linear, thus ensuring scalability.
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