Fracture Stimulation in a Soft Formation
Authors: Yarbrough C.L. , McGlothlin B.B. , Muirhead J.F. 
Published: December 2007

This paper was prepared for the 40th Annual California Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in San Francisco, Calif., Nov. 6–7, 1969. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
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Abstract
Hydraulic fracturing has been tried in an effort to stimulate production from a massive diatomaceous earth formation in Lost Hills Field, California. The technique, itself, was very conventional, but the application was unusual in that this formation is much softer than those in which fracturing is routinely used.
Preliminary to field application, laboratory tests were conducted on formation cores to investigate the problems of proppant embedment and fracture flow capacity under simulated overburden loads. The results of these tests indicated that production stimulation should result from fractures packed with complete layers of 10–20 mesh proppants.
The treatment design sought to circumvent the possibility of proppant embedment and consequent fracture closure by means of packed fractures. Through selective burrless perforating and a continuous eight-stage treatment perforating and a continuous eight-stage treatment utilizing sealer balls, the entire 750-ft interval was treated. The use of radioactive sand throughout the job, together with gamma logs before and after treatment, aided in evaluating the success of the operations.
A comparison of the radioactivity logs and recovery of the sealer balls clearly showed all the perforated intervals had been treated as planned. Vertical fractures were indicated. planned. Vertical fractures were indicated. In some cases, where intervals were not separated by sufficient vertical distance or by zones of significant porosity change, fractures initiated at different sets of performations appeared to join.
Early post-treatment productivity was somewhat better than that of offset wells. However, the production rate declined rapidly and after two months was essentially the same as the offset wells. The treatment was not economically successful.

Introduction
Volumetric calculations indicate that several hundred million barrels of oil are in place under Gulf properties in Lost Hills Field, place under Gulf properties in Lost Hills Field, Kern County, California.