A Field Case Study Of Differential-Pressure Pipe Sticking
Authors: Adams Neal 
Published: December 2007

Adams, Neal, Member SPE-AIME, Prentice and Records Enterprises, Inc. Prentice and Records Enterprises, Inc. Copyright 1977, American Institute of Mining, Metallurgical, and Petroleum Engineers Petroleum Engineers This paper was presented at the 52nd Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME held in Denver, Colorado, Oct. 9–12, 1977. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write: 6200 N. Central Expy, Dallas, Texas 75206.

Abstract
Differential-pressure pipe sticking has menaced the drilling industry since the industry's inception. A number of theoretical studies and laboratory analyses have been made in an effort to define and remedy the problem. However, as yet, very little work has been done in the analyses of differential-pressure pipe sticking field cases.
It was the general objective of this study to observe and define any relatable pipe sticking field case characteristics. When possible, an attempt was made to draw conclusions from these observed characteristics as to the best practical approaches in order to avoid or minimize these possible problem situations in the future.

Introduction
Differential-pressure pipe sticking occurs when the drillstring becomes embedded in a mud solids filter cake, usually across a permeable zone, and is held in place by an amount of differential pressure. Differential pressure is the difference between the drilling fluid hydrostatic pressure and the formation fluid pressure. This type of pipe sticking usually occurs after the pipe remains motionless in the wellbore for a period of time and is identified by no impedance of drilling fluid flow in the annular space and the inability to move the pipe in either vertical direction.
The principal methods used for releasing stuck pipe are costly and unsuccessful in a large pipe are costly and unsuccessful in a large percentage of the cases. These pipe releasing percentage of the cases. These pipe releasing techniques range from a chemical approach such as spotting fluids to mechanical methods including impact loading and hydrostatic reduction. Pipe release efforts are often applied indiscriminately and without forethought.

OBJECTIVES
An analysis of spotting fluid applications in field cases was made. The objective was to study the volumes of fluid spotted vs success ratios for these applications in an effort to determine minimum spotting fluid volumes that can be used to achieve maximum success ratios for field usage. Wellbore and drillstring characteristics were studied. An effort was made to define drilling intervals most conducive to sticking and the sections of the drillstring involved in the sticking process. Casing configurations and wellbore diameters were gathered to observe relatable pipe sticking tendencies or anomalies. The drilling fluids involved in each of the field cases studied were used to determine the fluid type most conducive to sticking. Also, a specific objective of the study was to define the amounts of differential pressure needed to initiate pipe sticking under field conditions. An effort was made to determine if the pressure differential was due to either excessive drilling fluid densities, formations pressure progressions that exposed upper zones to high fluid densities, or as a result of formation pressure regressions while maintaining a constant fluid density.

CASE STUDY METHODOLOGY
This study was approached from several different areas, the first of which was the gathering and analyzing of spotting fluid data. A spotting fluid is any substance, oil or water base, that is positioned in the wellbore to achieve a specific positioned in the wellbore to achieve a specific purpose. In this study, only oil-base fluids that purpose. In this study, only oil-base fluids that are used to attack the pipe-to-filter cake sealing mechanisms were analyzed since water-base fluids used for this purpose have not yet gained industry-wide acceptance. Some of the data gathered included the volume and density spotted, the success of the effort, and the type of fluid (oil- or water-base) that was displaced by the spotting fluid.
A second approach for this study was through the analysis of a modified sonic log that is used to detect free and stuck intervals of the drillstring.