This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Casper, Wyo., May 15–16, 1973. 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 paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract

Generalized methods for determining pore pressures and fracture gradients have been pressures and fracture gradients have been developed for the Rocky Mountain Area. These methods, utilizing sonic log data and wellsite measurements, are based entirely on empirical data.

A generalized fracture gradient chart and formation density overlay has been developed to assist in well planning and mud density control.

Introduction

Methods for determining pore pressures from logs have been used on the Gulf Coast, and accepted for several years. These methods have not been as useful in the Rocky Mountains and other "Hard Rock" areas; lithology changes are frequent and drilling may progress from Tertiary to PreCambrian rocks on a single well.

Known methods for determining fracture gradients generally yield much higher values than are normally observed in the Rockies. This may exist since much of this area is naturally fractured.

Shale density overlays developed on the Gulf Coast have little application at most Rocky Mountain drill sites. These overlays were developed for use, with good clean shales which are uncommon in the Rockies.

A method for predicting pressures from sonic logs 51 was developed by examining these logs and comparing them with mud records. High and low pressure zones can be defined from the sonic plot, and the maximum mud weight required can be estimated by using a simple method.

A fracture gradient chart has been prepared by using mud records and sonic log prepared by using mud records and sonic log data.

A formation density overlay developed from several observed wells is submitted as an alternate to those previously developed.

SONIC LOG METHOD

The conductivity and resistivity methods of pressure profiling provide erratic data in the Rockies, since good clean shales are hard to find. Sonic logs will provide excellent data that are affected little by lithology (Fig. 1) if the values are averaged. Either the one- or two-inch per 100-foot scale will facilitate data averaging.

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