Introduction

  1. Measure the pressure in a gas well using high resolution electronic recorders (resolution better than 1 kPa). Produce IE6 m3 of gas. Shut the well in until complete buildup and measure the pressure again. It is 100 kPa lower than the initial pressure. Does this mean depletion?

  2. The material balance relationship for a gas pool is an equation of a straight line. All you need is two pressure/production measurements to define this line. The ends of this line give you the initial pressure and initial gas in place. Does this mean we don't need to measure the initial pressure anymore. because we can determine it, a posteriori, from any two measurements'?

  3. Two pressure recorders (electronic, high sensitivity) sitting one metre (vertically) apart show a difference of 1 kPa. Is the fluid between them gas or water'?

From a science perspective the answers to the above three questions are very obvious: yes, yes, gas: but from an engineering perspective, the answers are: sometimes, no, maybe either. These examples are typical of the issues we face as engineers (particularly reservoir engineers), dealing with inaccurate data and trying to estimate unknowns, and sometimes "unknowables."

With the advent of the computer age, we have lost something precious; we have thrown out the baby with the bath water. Not only did engineers throwaway their slide rule, but with it some of us threw away the slide rule mentality - the art of approximation and judgment. I remember with the early electronic calculators the square root of 4 was not 2, it was 1999 It is also apparent that, with the advent of digital watches, time is no longer a continuum. but it occurs in discreet quantities such as seconds! (As seen on the LED display of the digital watch). This is the dilemma of our age.

Science and Art - Theory and Practice

Computers now calculate at the rate of millions of instructions per second. They have given us the ability to arrive at the answer faster. Usually the answer will be wrong! But if we are good engineers it will be the best possible answer. This underlies the essence of engineering (particularly reservoir engineering). We are usually working with extremely complex real life situations, idealized (simplified) models, precise but inaccurate data, incomplete data sets and conflicting data. We can study and compute multiple options based on several assumptions, each leading us to different conclusions. But, at the end of the day, in spite of the numerous solutions, we usually only have a choice of one of these options to act on.

Science and computers have provided us with the theory. However, superseding all this theory, must be the practice. Often this is a gut feeling, procedure based on experience of real life behaviour of systems. In other words, it is an art." Good engineering is an art based on both science and experience, theory and practice.

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