A Discussion on Some of the Factors Affecting Well Spacing

From the standpoint of getting oil from the reservoir sands our presentmethods of extraction are very inefficient. From all data compiled it isevident that about three times as much oil remains in the sand after economicproduction has ceased as was originally produced. Spacing is not so much a problem of determining how many acres a well willdrain as it is a problem of obtaining the greatest possible yield at theminimum expense. In this paper will be discussed some of the factors affectingyield to show how little we know about recovery and to indicate thepossibilities for further research along the suggested lines. Property linesand surface restrictions should be disregarded and the economic spacing ofwells should be governed by subsurface conditions. However, it is obvious thatall existing conditions, both surface and subsurface must enter into thisproblem. Some of the important factors affecting production are: Structural position;thickness, porosity and grain size of the sand; gas pressure and hydrostaticpressure; viscosity, capillarity, adhesion and surface tension of the oil;dissolved and occluded gases; isothermal expansion and the gas-oil ratio inlifting the oil. Structural Position An oil or gas structure is any arrangement of sand of such a nature as toform a trap suitable for the accumulation of commercial quantities of oil orgas. Structural position has an important effect on a well in that the life ofthe well, the amount of oil produced and the efficiency of the operation dependon this factor. The potential amount of recoverable oil is less at the limitsof the field and theoretically could be handled by a fewer number of wells. Butto prevent water coning and the bypassing of water with the resultantentrapping of oil, the wells should be spaced so that control can be maintainedover water encroachment. There is some justification for spacing wells near together in the directionof strike when it is assumed that the movement of oil is up the dip of thestructure. Theoretically a screen of closely-spaced wells along the crest ofthe anticline and across the direction of flow would completely drain it underthe influence of hydrostatic pressure.