PROBLEMS IN WELL SPACING Well spacing offers a number of problems. The number of wells needed to develop a tract of land depends not only upon the local geological conditions but upon the way the land is sub divided. If one company' controls ,a pool or a large acreage the well spacing is planned to meet the geological conditions.
It is well known that shallow tracts with low gas pressure 100 to 200 lbs. per square inch will require more wells than deep tracts with large pressures of SOO to 1000 lbs.of pressure. Shallow tracts 200 to 500 ft. deep will require one well to every 2 or 3 acres. On deeper tracts, say from 2000 to 3000 ft. each well will be given from 6 to 10 acres. There is no set rule regarding this, however. Economic conditions govern spacing.
In the Gulf Coast area of Texas one well per acre is the usual practice. In fields like North Central Texas where the wells come in with a high initial yield, spacing should be carefully studied. One well to 20 acres or even to 40 is all that should be allowed. In some fields where the wells are shallow, the gas pres sure very weak, and the sand thick, one well to 2 acres is not too many.
The tightness of a sand also determines the number of wells. A tight sand may require more wells than a very porous one. Some wells drain oil from neighboring wells especially where the sand is porous. In such cases wells on one's own lands should be spaced far apart so as not to interfere. However, line wells should be kept as close together as practicable to keep the neighbors from draining one's holdings.
In some fields like the Gulf Coast fields, wells have been placed on 346 of an acre tracts. This was especially true at Spindle Top during "boom" times, and resulted in great loss. The derricks in some places were so close that the derrick floors overlapped.
Town-lot drilling in shallow areas means close spacing. In such excitements one well to a 50 by 150-ft. lot is not unusual. Such close spacing means a tremendous waste of money as one well would obtain all the oil that a dozen or more would. The
history of Spindle Top, of Burkburnett, of Paola, Kansas, of Cleveland, Oklahoma, and of Los Angeles, California, all bear this out.
Wherever possible well sites should be made as the result of engineering advice. If the geologic structure can be deter mined the sites should be made to conform to the structure. To put such a plan into effect one or two companies should control the structure. This .plan must of course be varied to suit the local conditions but is an excellent one to obtain all the oil with a minimum number of wells. One decided advantage of such a plan is the maintenance of a gas reservoir at the top of the dome. As long as this reservoir remains untapped it will act like the air chamber on a force pump. The gas in the top of the reservoir tends to drive the oil downward to the wells on the side of the dome. Such a plan will only be successful where one or two companies control a field.
Natural Factors Affecting Oil Wells.—The natural factors in the handling of wells are : 1. Gas pressure.
2. Character of the oil sands, porosity, saturation.
3. Character of the oil, specific gravity, viscosity.
4. Effect of one well upon another.
5. Water conditions.
6. Number of oil strata.
Gas Pressure.—Gas pressures vary in every field. In the Mid-Continent and North Texas areas, in Louisiana and in West Virginia, initial gas pressures roughly run 40 to 43 lbs. per each 100 ft. of depth. In California, however, the pressures do not have this regularity.
The importance of conserving gas pressures must be fully appreciated. Gas is the natural expulsive force for oil and the dissipation of this pressure must be guarded against. The waste of natural gas due to allowing wells to flow into the air with the hope of bringing in oil is not only a national waste of valuable fuel but a loss of good lifting power as well. It is a known fact that as the gas pressure decreases the oil production also decreases.