American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

Abstract

Detailed downhole pressure measurements were made in two wells to observe the effects of pipe velocity and circulating rate in weighted pipe velocity and circulating rate in weighted oil-base and water-base muds. The effects of lost circulation material on downhole pressures in the water-base mud were also measured. A major conclusion is that control of the instantaneous (rather than the average) pipe velocity while tripping and making connections is necessary to minimize pressure changes downhole.

Introduction

The control of downhole pressures while drilling is an essential part of well control. Changes in downhole pressure result from drill string movement, pump operation, and changes in mud rheology and density. The addition of certain types of lost circulation material to control mud losses can increase mud viscosity and downhole pressures and therefore can aggravate the lost circulation problem. Knowledge of the downhole pressure at all times is of great importance to the success of any drilling program.

In view of a lack of published data on downhole pressures in various phases of drilling operations, a program was initiated to measure downhole pressures as they are affected by circulation rate, pipe velocity, and the addition of lost circulation material. Detailed pressure measurements were made in two wells, pressure measurements were made in two wells, one in a weighted oil mud and one in a weighted water-base mud. The effect of lost circulation material was determined in the test with a water-base mud. This paper discusses the pressure data obtained and the conclusions pressure data obtained and the conclusions derived from the data.

Background

The importance in well control of downhole pressure changes caused by circulating the mud and moving the drill string has been recognized for some time. In 1934, Cannon measured swab pressures due to drill string movement, and in 1951, Goins reported measurements of surge pressures resulting from drill string movement. Graphic descriptions of these pressures were given by Cardwell and Clark. The last reported measurements of downhole pressure changes were those by Wilson in 1962. Burkhardt and Schuh have described analytical methods of calculating downhole pressure changes. The authors have recently pressure changes. The authors have recently described a new computer program for calculating swab/surge and circulating pressures.

The previous measurements of downhole pressure changes have been very limited in scope pressure changes have been very limited in scope and in instrumentation.

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