General Oilfield Development Schemes Considered in Relation to Physical and Geological Conditions Influencing the Production of Oil and Gas Available to Purchase

Tam: geological conditions under which oilfields exist are briefly reviewed. A distinction is drawn between (a) Oilfield reservoirs in which edge-water advances rapidly as oil/gas is withdrawn; (b) Oilfield reservoirs in which edge-water does not advance appreciably as oil/gas is withdrawn; but there are types between these two extremes and in general the dividing line between the two is not sharply defined. The main features of the physics of oil and gas movement in the reservoirs are noted with particular reference to the factors affecting viscosity and surface tension, notably the effects of the association of gas with oil. The importance of permeability as opposed to porosity in reservoir rocks is also stressed. General oilfield development policies are discussed for reservoirs of types (a) and (b) above, mainly with reference to the relationship of development to structure. With regard to type (a), reference is made to the possibility of maintaining reservoir pressure, and hence the flowing life of wells, by regulation of production. For type (b) the alternatives of: is Development from the margins inwards, ii. Simultaneous development from crest to margins, iii. Development from the crestal area outwards, are examined and compared with special reference to the importance of the formation/extension of a crestal gas area. A brief examination of the problem of well spacing and interference of wells refers mainly to sandstone reservoirs. A discussion of the importance of the control of gas/oil ratios, and the effects of the application of gas drives, repressuring and pressure maintenance conclude the paper. In summing up the author suggests that two points are of fundamental importance A. The-desirability in all types of reservoirs of avoiding such unnecessary waste of gas as will result in the setting up of hindrances to the action of natural forces available for moving oil underground towards wells. B. The desirability in certain reservoirs of augmenting natural forces, not in the mechanical way of lifting oil from the bottom of the well by means of some form of pump, but by a properly controlled policy of gas injection. Something approaching pressure maintenance appears to be the ideal to be aimed at, and its importance may be such as to overshadow and perhaps to solve such questions as to whether, in reservoirs in which edge-water does not advance rapidly, development should be "marginal," "simultaneous" or "crestal," and its adoption may also change considerably current ideas as to spacing interval. at least delay, unlimited upward migration of oil. (c) Geological structure of such a kind as to allow of upward migration and concentration of oil. (a) Porous stratum.