DEVELOPMENT PROGRAM Location and Spacing of Wells.—The first problem which pre sents itself, when development of a tract of oil land begins, is the location of the first well and the determination of the area which individual wells shall be expected to drain. Frequently, the operator is allowed no choice in these matters, due to the fact that wells have already been drilled or started on neighbor ing properties so close to the boundary lines that it becomes imperative to drill "off-set" wells in order to prevent the neigh boring wells from obtaining an undue proportion of oil. A prop erty can be more profitably operated if agreements with neighbors are obtained so as to obviate competitive drilling, which usually entails an excessive number of wells profitable to neither party. The present discussion cannot cover all the phases involved in "line drilling" and agreements between neighbors, but will deal with general principles. These principles should be considered by a single operator holding a large property, and should be the basis of consideration between neighboring operators.
The first well on a property should be drilled at a location giving promise of yielding the greatest amount of oil and furnish ing information for guiding subsequent drilling outward towards the non-productive margin or limit. Where there are no wells in the immediate locality the first well will have to be located purely upon such evidence as is afforded by a geological study of the ground surface of the region. Consideration of the subject of purely geological investigations is beyond the province of this book. If there are producing wells in the locality, their physical condition and productivity will furnish evidence which may out weigh that afforded by mere geological study of the ground sur face. The following chapters set forth the manner in which evidence afforded by well drilling can be assembled and studied.
The distance between wells should be determined so as to ex tract most profitably the oil under a tract of land. This subject apparently has not been systematically studied, as frequent in stances exist where operators have made unnecessary expenditure by drilling an excessive number of wells. No definite rule can
be established which will meet all conditions. However, con sideration of some of the underlying principles, together with such facts as are at present available, should lead to further study on the part of operators, and would result in saving very considerable sums of money.
An example of unnecessary expenditure is afforded by the pro duction records of four wells shown in Fig. 1.
It will be noted that as each new well was completed there was a marked decline in the production of wells already completed; and that each new well drew much of its production from natural reservoirs previously supplying the adjoining wells. One well, or at most two wells, would doubtless have supplied as much oil as the four, which were actually drilled at a cost of about $50,000 each. Needless expense would have been avoided by regular observation and comparison of the production records of each of the wells. It will also be noted that the record of the total production of the entire group of wells leads, of itself, to the conclusion that each additional well was a benefit to the property, but the records of individual wells show that the utmost benefit was not being obtained.
The most profitable spacing of wells falls between two extreme limits, each of which would, of course, in practice be an absurdity. The limits depend upon the desired rapidity of production. The quickest way of removing all possible oil from the ground would be to drill wells as closely as possible to each other, in which event the output of each well would, in most cases, not repay its first cost. The opposite extreme would follow the assump tion that one well would, if given time enough, drain an entire pool. Physical conditions, such as obstructed channels, due to close grained rock or precipitated residue, eliminate such an assump tion, even though it were financially permissible to wait indefi nitely for production.