DISCOVERY AND IMPORTANCE OF INTERMEDIATE EDGEWATER Following is a brief summary of conditions and operations leading up to the discovery of the intermediate edgewater sand, which sand has been the principal cause of water trouble in the field.' A number of new wells, which had encountered what wa.g termed "bottom," water had been plugged off at the bottom. The depth to the top of the last plug placed, where water was ex cluded was noted and a table made showing the interval between the first main oil sand and the supposed location of the This interval was in every case approximately 300 ft., allowim: greater interval where the well was on the edge of the field to increase in dip.
With the assistance of Mr. A. F. Davis, Superintendent o' the Petroleum Midway Company, Ltd., an experiment ws tried in an endeavor to more closely determine the distance from the top of the first main oil sand to the top of this water sand. Water was shut off in their well No. "Baldwin" 5, Section 6, T. 2 S., R. 11 W., S. B. B. and M., some distance above the first oil sand, and the top of the sand logged as accurately as possible. Drilling was then continued about 130 feet below the top of the sand and the oil string was cemented. After cementing bailing test showed oil entering at the rate of about 3 bbl. per day. Drilling was then continued about 100 ft. further, perfor ated pipe was inserted and all fluid removed from the well. Bailing test showed oil entering at the rate of 6 bbl. and water bbl. per day. The perforated pipe was then removed and drilling continued 50 ft. further. Perforated pipe was then set on bottom and the well was bailed to 1100 ft. and filled up to 690 ft. in seven hours with water. Water could not be lowered below 1417 ft. by sixteen hours of continuous bailing.
The results of this test showed definitely the presence of an intermediate water sand, as wells higher on the structure were producing clean oil stratigraphically deeper than this water sand.
It also demonstrated that this water sand was an edgewater sand, since those wells higher on the structure were producing clean oil from the identical horizon which produced water at this well. For this reason this water sand has been termed the inter mediate edgewater sand. Upon examination of wells which encountered water in this sand, and comparison with wells which encountered oil in the same sand, it was not difficult to locate the line of edgewater.
McGinley Oil Company wells Nos. 3 and 4 are producing water and wells Nos. 1 and 5, only 300 ft. distant but up the dip, produce oil from the same sand. Following this edge water around the field indicates that the line of edgewater apparently conforms very nearly to the minus 2250 ft. con tour. It has definitely been proven that wells which tap this sand shallower than sea level minus 2250 ft., produce clean oil, while wells penetrating the sand lower than sea level minus 2250 ft. produce water. This creates a central dome around the apex of the anticline which is free from this intermediate edgewater.
The following wells have been drilled through the first zone and into or just through the intermediate edgewater and have been plugged in the bottom so as to produce from the first oil zone.
No PROVISION MADE FOR FUTURE PRODUCTION It is to be noted that nearly all wells drilled in the central dome, where the edgewater does not exist, are deep wells producing from both first and second zones. In these deep wells no provi sion has been made for encroachment of edgewater. This is due partly to the drilling policy which does not recognize the necessity for protection until water troubles appear and partly to the fact that underground conditions have become known since many of the deep wells were drilled. In new wells to be drilled to the second zone, in the central dome, account should be taken of the possibility of encroachment of edgewater as the oil is with drawn from the intermediate edgewater sand, so that a change in casing program at a later date will be unnecessary. This might be accomplished by cementing an oil string below the first zone and intermediate edgewater sand, which at this point would carry oil, and producing from the second zone only until such time as this zone is exhausted, when the bottom of the well could be abandoned and production obtained from the upper zone, together with the edgewater sand, until edgewater began to appear in the edge sand which could then be plugged off. The possibility of producing from the third zone may suggest some Dther plans.
Under present conditions it would seem that the more oil that is drawn from the edge sand in wells now penetrating same, the faster will be the encroachment up the dip in the direction of maximum withdrawal.