Gas Proration In The San Juan Basin
Authors: Arnold Emery C. 
Published: December 2007

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This paper is to be presented at the Four Corners Regional Meeting of the Society of Petroleum Engineers to be held in Farmington, N.M., on Sept. 18–18, 1964, and is considered the property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of Journal of Petroleum Technology or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in Journal of Petroleum Technology or Society of Petroleum Engineers Journal is granted on request, providing the proper credit is given that publication and the original presentation of the paper.
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Introduction
Natural gas has been produced commercially in the San Juan Basin of Northwest New Mexico since the early 1920's. Development was minor until late 1951, when our first major market was established in California by the El Paso Natural Gas Co. Ninety-five per cent of our natural gas development has taken place since 1951.
As of Jan. 1, 1952, there were about 300 producing gas wells serving local New Mexico and Colorado markets. As of Jan. 1, 1964, there were 5,920 wells producing gas. Total cumulative production to Jan. 1, 1964, was 2,973,010,197 Mcf.

PICTURED CLIFFS SANDSTONE, MESAVERDE FORMATION, AND DAKOTA SANDSTONE
Gas development since 1952 has been at a steady rate of from 300 to 650 wells per year at an average rate of 500 wells per year. Ninety-seven per cent of our gas production comes from three geologic formations, all within the Cretaceous System. These are the Pictured Cliffs Sandstone, Mesaverde Formation and the Dakota Sandstone.
The most important controlling mechanism for the accumulation of gas in each of these formations is rock characteristics. The Cretaceous System in the San Juan Basin consists of thick shale sections with intervening sandstones. Within specified areas, wherever these sandstones develop sufficient porosity and permeability, natural gas has accumulated. For this reason, the occurrence of gas is very wide-spread geographically and the dry hole ratio for development wells is very low.
The Pictured Cliffs Sandstone is the shallowest of the major producing zones and ranges in depth within the producing areas from 1,000 to 4,000 ft. There are 10 Pictured Cliffs Pools as defined by the Oil Conservation Commission, all of which represent sandbar accumulations along buried shore lines. Approximately 2,500 wells are producing from this zone. These wells were all developed on 160-acre spacing. Mesaverde gas production comes from a huge, fairly well defined stratigraphic reservoir which is approximately 70 miles long and 40 miles wide. Depth ranges from 4,000 to 6,000 ft. Approximately 1,900 wells are now producing in the Blanco Mesaverde Pool. This pool is developed on 320-acre spacing and is still not fully developed.
The third major gas producing horizon is the Dakota Formation, which varies in depth from 6,000 to 8,000 ft. within the producing area. The Basin Dakota Pool is defined by the Commission as being that area which is productive of gas from the Dakota in San Juan, Rio Arriba and Sandoval Counties.