Abstract

An inexpensive computer program, utilizing the graphical capability of the IBM-PC, has been developed that demonstrates and teaches the control procedures to be used as the result of a gas kick taken during drilling. In order to properly diagnose and control a kick, one must have a complete understanding of what is happening downhole and why. The color simulation that is presented in this paper - which can be run in real-time or accelerated time - aids in this understanding process. The status of the drilling process, as well as the critical surface measurements available, are displayed graphically on the screen before, after, and during the control of the kick. The display shows the gas bubble, its growth as it is circulated out of the hole, locations of all of the different fluids that are involved in the system (drilling mud, kill mud, and gas bubble), and the surface effects that occur during the control procedure.

The program can be run in either a demonstration mode or a control mode. In the demonstration mode, a kick is circulated out by the computer by both the driller's and the wait and weight methods, using the ideal control procedure. An instructor can utilize the demonstration to point out particular points of interest during the process. In the control mode, the operator of the program uses the keyboard to control the process. That is, he or she has direct control of the mud weight to be pumped, choke opening, and pump speed. At the conclusion of a run in either mode, graphs are produced of various pressures as functions of the number of strokes pumped.

In the control mode, the program monitors the correctness of the control scheme and highlights incorrect procedures that would result in either a low bottom hole pressure, causing a secondary kick, or a high pressure at the bottom of the casing, causing a loss of circulation.

Introduction

The study of drilling is obviously an important part of any petroleum engineer's education and one topic in that area that can be particularly difficult to teach is the proper control of the system during a threatened blowout. Podio, et al recently compiled statistics for blowouts in the Southeastern US and the Gulf of Mexico and suggest that blowouts, defined as "an uncontrolled flow of formation fluids to the surface" are occuring at approximately one per 1000 wells. During the boom years of 1977-78 when much of the drilling activity was supervised and performed by inexperienced people the rate dipped as low as one blowout per seventy-five wells for offshore Louisiana. The massive personnel reductions of the past few years suggest that renewed activity will lead again to inexperienced supervision. Although there are a number of simulators available to the industry, these are too expensive for the average academic department to own and maintain, hence a microcomputer based program has been written for an IBM-PC, or compatible, that both demonstrates and teaches the concepts by allowing hands-on experience for the students. Podio, et al also indicates that of 228 events, 101 blewout while tripping and 94 while either drilling or circulating a kick. The simulator only addresses the problem of circulating a kick but an understanding of the principles involved during kick circulation would certainly aid in the decision making process during other operations.

As a review of the basic concepts involved, the following discussion is offered. During the drilling of a hole, the engineer utilizes a drilling fluid that has a number of purposes such as lifting the cuttings, cooling and lubrication of the bit and drill string, and control of subsurface pressures. It is the hydrostatic pressure of the mud that is of interest in this paper. In certain geologic areas there is a potential to drill into an overpressured gas zone.

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