Practical Considerations in Pressure Control Procedures in Field Drilling Operations
Authors: Grace R.D. 
Published: December 2007

This paper deals with three common problems in practical pressure control. Limits of the use of heavy muds are defined. Practical considerations are considered that are necessary to bring a well under control with heavy mud. Also, new technology is proposed for killing a flowing well that is completely out of control.

Introduction
Pressure control procedures are becoming classic in most areas of the world. However, some common field procedures in well control need to be evaluated in terms of the most recent developments to avoid unnecessary field problems during kill operations. The purpose of this paper is to evaluate three specific field problems.
In many instances, the maximum anticipated casing pressures will exceed the fracture gradient at the casing seat. As a result, dangerous and unfounded control procedures1 have developed, such as the low-choke-pressure method. A well founded alternative, offered by Moore,2 introduced a slug of heavy mud ahead of the kill mud to control and reduce the maximum pressure at the casing seat. This paper extends and defines this approach.
Another common problem in areas with varying fracture gradients occurs when a column of heavy mud is used to bring a well under control. Routinely, the choice of mud weight and volume to be used is rather arbitrary. Often, as a result, the well is not brought under control. This paper offers the considerations necessary to result in the successful optimum control of the well.
A third common problem is how to bring a well under control that is completely out of control. Routinely and classically, the industry thinks in terms of killing the well from the bottom. Equally routine in air drilling operations, experienced field personnel will strip up into the protective casing to bring a well under control. Hence, the bottom may not always be the proper place to be in a kill operation when the well cannot be shut in. This paper analyzes the considerations and offers calculations to be used in determining the proper place for kill operations.

Discussion

Controlling the Annular Profile
When a well kicks, the operator is concerned primarily with displacing the kick without losing circulation. It has been shown3 that the maximum annular pressure occurs at the weakest point, which is usually just below the casing seat, when the top of the gas bubble reaches that weakest point. It should be noted that, although circulation is generally not lost when the well kicks, circulation could be lost readily when the gas bubble reaches the weak point. The result is an underground blowout. Proper planning would eliminate some of these problems. The problem is best illustrated by an example.

Controlling the Annular Profile
When a well kicks, the operator is concerned primarily with displacing the kick without losing circulation. It has been shown3 that the maximum annular pressure occurs at the weakest point, which is usually just below the casing seat, when the top of the gas bubble reaches that weakest point. It should be noted that, although circulation is generally not lost when the well kicks, circulation could be lost readily when the gas bubble reaches the weak point. The result is an underground blowout. Proper planning would eliminate some of these problems. The problem is best illustrated by an example.