Book Review

Geomechanics in Reservoir Simulation,

edited by Pascal Longuemare,
ISBN 2-7108-0833-1, Editions Technip, Paris, 2002, 192 pp US $70.

The “Geomechanics in Reservoir Simulation” text published by Editions TECHNIP in 2002 represents a collection of 14 selected papers from the IFP symposium on geomechanics held in Rueil-Malmaison, France, over December 5-7, 2001. The papers reflect the organization of the conference into four themes: Case Studies, Numerical Methods, Reservoir Management and Well Modeling. The initial conference was organized as a program within the series of “IFP Scientific Meetings” with the objective to provide a forum for academic and industry representatives to exchange and discuss their experiences within emerging technical fields of interest in the petroleum industry.

As such, the text provides a general overview of current thoughts and research to the application of geomechanical physics to the flow modeling of fluids in hydrocarbon reservoir simulation. The collection of papers provided do not form a comprehensive text in geomechanical reservoir simulation as a guide or introduction to the uninitiated in the field. While this may provide a disappointment for many, the intent of the collected papers is to demonstrate a profile of recent developments and applications of geomechanics. To this, the text is successful in demonstrating the emerging nature of the field of geomechanics in the more traditional field of reservoir simulation.

Geomechanical considerations are demonstrated to be of concern in reservoir environments on the fringes of classical modeling: poorly compacted reservoirs, geothermal applications, shallow steam injection processes, etc. In addition, consideration is demonstrated to the potential for the reactivation of faults in highly fractured and/or stressed reservoirs. However, definitive examples of the relevance of geomechanics to more conventional reservoir environments is limited. This serves to illustrate that the role of geomechanics to more common field operations remains an emerging field. However, as a first step, significant progress in the discipline of coupling geomechanical physics to conventional flow simulation models is well illustrated in the text. Progress in the simulation technology is a necessary precondition for the development of practical applications for geomechanical modeling to future reservoir studies.

The role of geomechanics in drilling engineering, such as wellbore stability considerations, completions engineering, such as hydraulic fracturing applications and subsidence calculations has been long established. In addition, there is a growing recognition that specific recovery technologies such as steam injection carry extensive geomechanical considerations for accurate reservoir performance modeling. However, in more conventional reservoir operations, the recognition and acquisition of relevant geomechanical reservoir data is a common limitation to the application of geomechanical modeling in environments of direct interest, such as waterflooding. Several papers presented within the text address the nature and utility of geomechanical reservoir characterization, which in itself presents numerous emerging technologies. The range of necessary data required to characterize geomechanical effects is of key interest to the initialization of geomechanical simulation models. To this issue, the text offers a range of insights into the current state of the art in geomechanical reservoir interpretations.

As the field of geomechanics is much more developed at a wellbore scale, illustrations and examples of wellbore phenomena are well represented within the text examples. However, the more general applications of geomechanics at a reservoir scale form the challenge of the emerging state of the art in the field. Current difficulties with reservoir scale geomechanical characterization are broadly presented within the collection of conference papers. These challenges result in a range of limitations with reservoir scale examples of geomechanical effects, illustrating the leading edge of geomechanical applications in practice.

Pascal Longuemare has provided an excellent collection of conference papers, which are helpful to the interested readership in providing an orientation to the broad range of geomechanical considerations in petroleum engineering and reservoir simulation. The text is well illustrated and presented, but is more oriented to readers with an existing background in reservoir simulation and fundamental geomechanical physics. The papers presented are thought provoking in guiding the reader to reconsider the role of geomechanics in more prevalent applications such as fault reactivation for fractured reservoirs, the effects of thermal stresses in water injection applications with large temperature differences between formation and injected water temperatures and variations in reservoir responses for reservoirs with well defined stress dependent permeability. The text provides a useful role outlining the potential impact of geomechanics to many challenging environments, particularly influences within fractured reservoirs, which can be highly complex. To this end, the book well illustrates the introductory comments of the keynote conference speaker, Jacqueline Lecourtier, that many geomechanical processes are still difficult to both quantify and model and that “the complexity of the problems encountered entails close collaboration between academic and industry researchers to make effective progress.”

In summary, the strength of the text is to provide the reader with a good overview of the state of the art in the application of geomechanical physics to reservoir simulation studies. While the presentation is not intended to provide a grounding for novice to the field of geomechanics, many fundamental issues in the application of geomechanics to reservoir modeling are reviewed, which do provide interesting reading for an audience at diverse levels in geomechanical studies. “Geomechanics in Reservoir Simulation” will be a welcome read for anyone with an interest in receiving an update on current developments in the field.

Mauro Cimolai
Core Laboratories
Calgary, Canada

Integrated Reservoir Studies

by Luca Cosentino.
ISBN 2-7108-0797-1, Editions Technip, Paris, 2001,310 pp US $85.

This book addresses the integrated reservoir characterization studies that have often demonstrated reservoir management productivity gains. Characterization of reservoirs though important is complex in that it attempts to bring together team members and a variety of data from a number of disciplines. The author therefore deserves credit for writing on such a topical subject and the book will find favour with a wide section of geoscientists engaged in such studies and sustain the interest in this area. The writing and presentation of this complex subject is quite clear.

After an illuminating foreword written by Jean-Claude Sabathier, chapter 1 elaborates on the philosophy of integration, the issues therein and how an integrated reservoir approach can successfully achieve the objectives of such a study. Historically, the professionals involved, i.e. geophysicists, geologists, petrophysicists and reservoir engineers usually have been using their own interpretation packages with limited interoperability as they do not share a common working platform and a common E & P database. This issue is addressed in chapter 2, where an effective approach to data management and software integration is discussed.

The construction of an integrated geological model that honours not just the available static information but the dynamic information as well is discussed next in chapter 3. This is done by bringing in the different elements in stages, viz. the structural and stratigraphic components, the lithological subdivision and the impact of internal inhomogeneties within the reservoir. While the first two elements provide the reference geometric framework for the reservoir, the next two elements serve to populate this framework with lithological characteristics and their variation and evaluate the internal geometry of the reservoir in terms of continuity and communication of the formation subunits respectively. The author has done a good job here bringing in detailed description in a systematic manner into the skeleton workflow mentioned above.

Once the geometric framework for the reservoir is finalized, the next advisable step is to add the petrological and petrophysical description to the reservoir rock so that it correctly represents the dynamic behaviour of the field at the numerical simulation stage. All this is described in chapter 4 in two stages. Beginning with the basics of rock properties, many investigation techniques are described for studying the reservoir properties of interest , including pore system characteristics and for integrating core and log information at the well locations. This is followed by a discussion focused on lateral variation of this estimated information so as to generate 2D and 3D distributions at the reservoir scale.

The next logical step in the sequence is to make use of the reservoir properties determined so far ( internal and external architecture and rock properties characterization) and estimate the amounts of oil and/or gas in place in the reservoir. This forms the topic of discussion in chapter 5. While such volumetric estimates seem trivial, both deterministic and probabilistic evaluations are discussed. This is followed by the discussion of the calculation of the hydrocarbon originally in place in the reservoir.

Chapters 6 and 7 tackle the next important phase in an integrated study – that of reservoir engineering. Chapter 6 reviews the basics involving the collection and analysis of the basic dynamic data of the reservoir in terms of rock and fluid parameters, and the pressure data, production and injection performance. This is quite an exhaustive description of the mechanisms, properties, analysis and distribution of fluids driving or affecting the reservoirs. Numerical reservoir simulation forms the subject of discussion of chapter 7, and assumes importance as it affords a way of estimating the future behaviour of petroleum fields and hence cash flow predictions. Carried out on fast computers and using numerical techniques involving the solution of finite difference equations describing multiphase flow in heterogeneous media in two and three dimensions, numerical reservoir simulation yields the estimated oil production profiles. The topics discussed here, designing the simulation model, the choice of the grids, assigning the reservoir properties to the grids, history matching and production forecasts along with uncertainty assessment.

The last chapter is devoted to the planning of an integrated reservoir study. An appendix on Material Balance is a useful addition/ backup for use of this equation in reservoir engineering basics in chapter 6.

After all the introductory and descriptive chapters, as a reader, I was expecting to see the integrated approach to a reservoir study outlined so far, put into practice. Unfortunately, no case studies are included and this is a disappointing feature of the book. The foreword to the book mentions that the author has managed several integrated studies on various types of reservoirs for oil and consulting companies. It would have been really beneficial to see some case studies included as well.

Some of the captions are brief and the illustrations would have benefited, if they were a little more descriptive. The shortfalls also include a few printing or grammatical errors (e.g. ‘then’ is seen in place of ‘than’ in a number of places). Probably, in the interest of keeping the cost of the book affordable, the images included as illustrations are printed in black and white. It would have helped appreciating the detail or understanding the conclusions better had these images been in colour (especially these days when we a re used to seeing such pictures in colour everywhere).

In spite of these shortcomings, I recommend this book to anyone involved in integrated reservoir studies aimed at integrated reservoir characterization. Even for use as an introduction to such studies, the book will serve as a very good reference.

Satinder Chopra
Calgary, Canada