Prediction of Reservoir Behavior from Laboratory Data

Abstract

In order to explore the possibility of predicting reservoir performance fromlaboratory data, behavior of a hypothetical low-permeability reservoir has beenestimated by applying data and methods currently available in the literature. Amethod of calculating decline in productivity index is discussed, andrecoveries by internal gas drive, external gas drive and water drive areestimated. Introduction During the life of a producing oil property an operator is faced with manyperplexing problems. Any attempt to determine proper well spacing, optimum rateof production, or the desirability of pressure maintenance requires theevaluation not only of a host of economic and practical operating factors butalso of the future performance of the reservoir. Although in some caseseconomic or operating considerations may be of primary importance in planning adevelopment or production program, the anticipated effect on ultimate recoveryis more likely to be the decisive factor. The soundest basis for evaluating reservoir performance is past experience withoil fields, but pertinent data are difficult to obtain or apply underconditions normally encountered in California fields. Many of these fields arecharacterized by thick sections of alternating sands and shales complicated byfaulting and rapidly changing lithologic conditions. Further complications areintroduced by haphazard development and production practices resulting fromcompetitive conditions, changing demand for oil, and insufficient knowledge ofstructural conditions during early development. Even in the rare cases wheredevelopment has been systematic and adequate, production policy has usuallybeen controlled by economic and competitive factors rather than a desire toobtain information for use in future operations. In other words, comparablereservoirs in which development and production practices have beensystematically varied are seldom found. In the light of these conditions, conclusions based on experiences usually lackthe certainty required for decisions involving large sums of money. Some othermethod of attacking these problems is needed to supplement and orient fieldexperience. Progress in laboratory investigations of the flow of oil, gas, andwater through sands has been so rapid in recent years that these data mayfurnish such a supplementary approach in the near future. In order to explorethis possibility the author has attempted to predict the behavior of one typeof reservoir by applying published data and methods. Basic Data and Assumptions Calculations outlined in this paper are dependant upon a detailed knowledge ofthe properties of oil, gas, and water present in the reservoir and the portionof the total pore space originally filled by each. T.P. 1664