Joint Meeting of the Rocky Mountain Petroleum Sections of AIME, 3–4 March, Denver

Introduction

Paradox - what is it? Webster says, "Paradox - an assertion or sentiment seemingly contradictory, or opposed to common sense, but that yet may be true in fact." Whoever the genius was who chose the name "Paradox Basin" certainly hit the nail on the head. As far as drilling problems encountered therein, almost anything can be said and still be "true in fact".

There is very little that one can say with any degree of certainty that will occur from location to location, and at this stage of development there is little unanimity of opinion or programs on the part of engineers, geologists, drilling contractors, or other interested parties.

Producing Formations

Most of the production so far discovered is in several zones of the Hermosa, ranging from the Upper Hermosa to the Lower Hermosa or Paradox above the salt. The geologists have not seemed to come to full agreement on various names of the zones or on whether it is all reef production or structural, trap, or combination of both.

Depths

In drilling these Pennsylvanian formations to the salt the depths will range from 4800 to 6300 ft. In general, the average north of the San Juan River will run about 5800 ft. South of the river the average will be around 5300 ft. Relatively few tests have been drilled through the salt, but these have added another 1000 to 1200 ft. The present search seems confined mainly to formations above the salt.

Casing Programs

Here, depending on the operator and the individual well conditions, there is great variation. Table 1 shows some of the typical programs in use in the area. The most popular programs are B and C. The variation in depths of the surface strings is usually due to the underground water conditions. While frequently omitted, it is usually good practice to set the conductor string. This is especially true on locations where there is a probability of water flow or where either shattered surface formations or heavy new fills would be likely to cause lost circulation. Sometimes this is set ahead of time with a so-called "dry hole digger".

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