Dindoruk	Johnson

Executive Editors of SPE Reservoir Evaluation & Engineering alternate writing the Executive Summary. This issue’s summary is by Alan Johnson.

As I mentioned in my first editorial, I work as a petrophysicist and have done so almost full-time for the past 30 years. My work mainly has been at a fairly practical level: operational duties, logging and core-analysis programs, wellsite supervision, quick-look analysis, and follow-up on to more in-depth study work generating fieldwide input to volumetric analysis, geocellular modelling, and dynamic simulation. All of this work has been aimed at specific goals, and I have to admit that I have had little day-to-day involvement in the more esoteric aspects of petrophysical research.

My preferred approach to petrophysical analysis, which has stood me in good stead over the years, is to keep things as simple as possible: a density-log-based total porosity, Archie clean-sand water saturation, and a basic sand/shale differentiator to identify reservoir intervals. With such an approach, I believe little can go wrong, at least on a first pass. I know others who also adopt similar standard strategies, perhaps substituting a density/neutron effective porosity and some other slightly more complex saturation algorithm on a routine basis.

Some might question why, with such a basic no-frills approach to my work, I should take such an interest in the literature produced for and by our Society. The papers that pass through my online task list (some 180 since I took on this post last October) deal with all manner of detailed studies, improvements to existing techniques, and new and innovative tool and equipment designs and applications. Some do indeed present examples of how these tools, methods, and techniques have been applied positively in practice. Nevertheless, one could ask what relevance these have to my everyday work.

While I am a great advocate of a simple, standard, first-pass approach, there are often distinct pitfalls if this is taken to be the final answer. In most cases, in my experience, the simple approach has served to highlight more complex aspects of the reservoir in question, perhaps significant shale response, thin-bed effects, complex mineralogies, dual-porosity systems, or other challenges. In almost every reservoir there has been something that required more than the simple standard approach to fully characterize or quantify it. These are the areas in which a more in-depth understanding of new developments may be of benefit.

What I have referred to above has focused on my own particular discipline, petrophysics, but in essence, the same view could be applied across the full spectrum of petroleum disciplines. Whatever our particular areas of focus, it behoves us all, as technical professionals, for our own professional growth and for the benefit of the projects on which we work, to keep abreast of the latest developments in our respective areas.

While I believe that it is usually a mistake to rely on the simple first-pass approach to our analysis for a final answer, the reason I prefer that approach is that I have also seen serious errors resulting from adopting an excessively complex process from the outset. Complex approaches tend to introduce more data noise and usually result in a higher degree of uncertainty in the final answer than more simple methods.

As a practical example, a group with whom I once was involved had a problem with cleaning core samples taken in a formation with halite-cemented sands. Conventional cleaning fluids dissolved the halite and caused the plugs to fall apart. The solution they landed on, which is perhaps fairly obvious, was to devise a cleaning program that did not remove halite. The downside of this was that it also did not remove salt deposited from the formation water or drilling mud, resulting in some underestimation of measured porosities. Given the difficulty of obtaining porosity measurements by any other method, this increased level of uncertainty was considered acceptable. Unfortunately, buoyed by their success, this core-cleaning approach was hailed as a new breakthrough and somehow became the standard technique applied to all future cores, even those with no problem of halite cementation. This resulted in the same level of underestimation of porosity being unnecessarily carried into these fields.

My message is, therefore, do not make the mistake of adopting a routine approach that is either too simple or unnecessarily complicated. Start simple and add the complexity you need to get to where you want to be.

In the papers in this edition, you probably will not find many examples of oversimplifications, but you may well find those gems that will help to unravel the unique complexities of your own particular field, reservoir, or area of work.