The Engineering of Hydraulic Fractures--State of the Art and Technology of the Future
Authors: Cleary Michael P. 
Published: December 2007

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering.

Summary.
A new age is dawning in the application of computers to preciseengineering design and analysis for the optimization of petroleum fieldoperations, particularly hydraulic fracturing. This progress is based on rapidimprovements in equipment, materials, model analysis, and computer-basedmonitoring of operations in the field, allowing real-time evaluation andimmediate feedback control of each process as it evolves in each unique set offield circumstances. Much has been written about equipment and materials. Thisreview concentrates on the dramatic changes in technology generated by thepower of computer-based analysis and design, based on sound engineering modelsof the process. Such engineering has gradually replaced guesswork, as researchand development have proved their value over the past decade or so. Primaryresults include more realistic fracture treatment designs, better qualitycontrol, and the possibility of largely automatic control for such operationsin the near future.

Introduction
Because it is a well-established technology for the vital task of improvingproduction from otherwise marginal or uneconomical wells, hydraulic fracturinghas been discussed thoroughly in the petroleum literature. We will referencethis extensive literature to avoid lengthy description of the many facets thatneed discussion in any comprehensive coverage of the topic. In particular, wemake primary reference to previous papers and an SPE monograph now inpreparation that present extensive discussions of most major aspects. Anoverview of the subject is provided in Fig. 1A, which leads to a naturalsequence of the main topics:geology and logging for overall reservoirevaluation,prefracture testing of production to estimate reservoireconomics,design of hydraulic fracturing treatments on the basis of Topics1 and 2,detailed selection of materials, fracture fluids, and proppants,field implementation and quality control of field operations. andpostfracture well testing to evaluate effectiveness/economics of treatment.
Acomparison of the forthcoming SPE monograph with the previous hydraulicfracturing monograph, now almost 2 decades old, shows that much progress hasbeen made on some aspects of the process; other aspects, however, especiallythe effective use of computers, are still at a retarded stage relative to otherindustries. Still, one chapter in the new monograph does demonstrate theincreasing role of computers, and this paper will expound on that theme. Thebasis for this increasing confidence in the use of computer-aided analysis anddesign, so common in other engineering areas, has been the result of extensiveefforts by many groups to measure, analyze, and verify by all means possiblethe detailed components of the hydraulic fracturing process. Discussion of allrelevant work cannot be included here, but Refs. 1 and 2 and the upcomingmonograph do provide a reasonable cross section of other references. The workmay be organized according to Fig. 1B, involving a number of categories, broadly grouped as follows:geological descriptions and wireline loginterpretation techniques;reservoir engineering--i.e., the details ofmultiphase flow in porous media;the mechanics of rock deformation andfracturing;the rheological behavior of fracturing fluids and proppant;the conduct of laboratory experiments to check model predictions;theconduct of field experiments to check model predictions; andthedevelopment of equipment and instrumentation for field implementation.
Inprinciple, the results of Category 1 should supply enough information for useby models, on the basis of a combination of Categories 2 through 4, to generatepredictions that check out against the results of conclusive experimentsconducted in Categories 5 and 6; after such thorough testing of the engineeringaspects, the technology would be implemented in Category 7. All of this isshown schematically in Fig. 1B, which also shows that the central aspect of themethodology is the availability of good fracture models.
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