Saxet Oil and Gas Field, Nueces County, Texas

Abstract

The Saxet field was known as a gas field from the date of the completion of the discovery gas well in January, 1923, until August, 1930, when the first oil well was completed. Since that time the history of the field has been a combination of a series of discoveries of new sands, most of which came at a time when the field no longer appeared to hold possibilities of additional production. The field has produced more than 42 million barrels of oil from 30 different sands and in excess of 200 billion cubic feet of gas exclusive of wastage, and on March 1, 1940, had a daily allowed production of 17,320 barrels of oil and distillate and an estimated 155 million cubic feet of gas. 893 wells have been drilled in the 9,100 productive acres, 560 of which still produce oil and dis illate. The highly faulted conditions presented by the field together with its many producing sands make a complicated but interesting problem, the solution of which would have been impossible without the use of electrical logs. A major fault curving through the field from northeast to southwest, and downthrown on the east or coastward, divides the field. Closure pattern is complicated by smaller and compensating faults which form a step-graben on the downthrown side of the major fault. Cross sections made up of electrical logs clearly show that small faults on the upthrown side of the major fault at places intersect in such a manner as to result in a graben in the upper beds which is underlain by a horst in the lower beds. The structure on the upthrown side of the major fault is an anticline trending northeast and southwest and faulted on both flanks while on the downthrown side the structure is a broad nose, arrested by several minor faults and gently plunging southeast. An unconformity is shown by movement of several of the minor faults on the upthrown side of the major fault having ceased with the deposition of the thickest member of the Greta sand series. That movement along the fault planes was coincident with deposition is shown by a thickening of section for the downthrown block as the fault plane is approached, resulting in an increased throw with depth. A study of oil accumulation indicates that the original structure was on the upthrown side of the major fault. Strong evidence for the migration of gas along the plane of the major fault is presented by the many high y charged shallow gas sands on the downthrown side. Most of the field's blow-outs have resulted from these sands.